: Regular vs Premium Gas



Mitch3
09-01-05, 02:32 PM
OK so as of today, Premium gas has hit $3.49 and up depending on where you buy it. I'm in upstate NY and I know many of you are paying more. Off and on I have put regular fuel in my 94 Eldorado. It runs OK but honestly no where near as good as with Premium. Here's my question.......If I use regular on a steady basis do you think I will harm my engine? I can't believe that some stations are charging as much as 70 cents more for premium vs regular. My son-in-laws dad has a 96 STS and if he uses regular he gets a "Check Engine" message. I don't have any visible problems, it just doesn't have the pep etc. as it does with premium. My manual says I have to use premium. Going broke and need your advice. HELP PLEASE.........

EcSTSatic
09-01-05, 02:39 PM
Search and you'll get a rehash of several threads on this!:banghead:

You have a knock sensor. It will retard your timing to prevent damage

Ranger
09-01-05, 03:30 PM
Northstar will run just fine on regular. I have been using it for over three years. As mentioned, search the archives. :horse:I suspect a lot of the diehard premium only for my car guys will start changing their tune very shortly.

chance_b
09-01-05, 04:45 PM
once i get my engine back in, i plan on only filling up with premium every 4 or 5 tanks, just to cleanse things out.

Mitch3
09-01-05, 05:30 PM
Thanks. I appreciate the feedback. I have read a lot of the past archives but it still bothers me that Caddy emphasizes the fact that you MUST USE PREMIUM FUEL. My mother-in-law drives a big ass 1994 Buick with a big 8 and her manual says to use regular unleaded fuel. I think Cadillac is the only manufacturer that ever specified premium fuels since way back in the 60's. I tend to trust you guys more than GM so I will go with regular. BY THE WAY.........has anyone noticed that their mileage has dropped since this CRAZY GAS SHORTAGE !! started? I have always gotten 23 miles per gallon around town. All of a sudden my mileage has dropped to 20 mpg. Several other people in my office have checked and have found the same thing. Sounds like someone is playing games other than our government. We know they are playing games.

jsjag
09-01-05, 06:01 PM
OK so as of today, Premium gas has hit $3.49 and up depending on where you buy it. I'm in upstate NY and I know many of you are paying more. Off and on I have put regular fuel in my 94 Eldorado. It runs OK but honestly no where near as good as with Premium. Here's my question.......If I use regular on a steady basis do you think I will harm my engine? I can't believe that some stations are charging as much as 70 cents more for premium vs regular. My son-in-laws dad has a 96 STS and if he uses regular he gets a "Check Engine" message. I don't have any visible problems, it just doesn't have the pep etc. as it does with premium. My manual says I have to use premium. Going broke and need your advice. HELP PLEASE.........

Well your question is always one that usually starts a fire. From what I have been told, as long as you don't get any pinging on regular unleaded, run with it. What I've been told the higher the compression ratio the higher the octane rating that will be given by the OEM. That doesn't mean that your car won't run on 87 octane nor does it mean you will ping.

I've been told the higher octane will not produce as much (can't think of the term) but as much heat. So on a hot day 87 octane could give you ping but a higher octane won't ping.

I belive that most octance grades have about the same amount of detergents. The mention of detergents......I think I read that modern gasolines don't have as much detergent as it once did.

MWA
09-01-05, 07:50 PM
Figure the difference out per year. Why not put what the manufacturer recommends in it? Ranger, I thought you would recommend premium, because GM designates it that way. I have saved enough over the many years period that I owned Honda's, (1978-1993) if all of the fuel expense was prorated.

Premium is still a mighty good buy.......for a Northstar. After who ever wants to drill where ever gets to drill what ever, it will come down. I never gave cheap oats to any horse that I owned either. Always followed Mr. Honda's manuals. Now that I own a premium automobile that suggest premium, I buy it. When I can't afford to buy it, I will purchase another automobile....but I have had the exquisite pleasure of driving the "best."

Many thanks, Ranger!

Ranger
09-01-05, 09:25 PM
jsjag
From what I have been told, as long as you don't get any pinging on regular unleaded, run with it."

The Northstar will not ping. It has a knock sensor that will detect spark knock long before you hear it and retard the timing appropriately.

MWA
"Ranger, I thought you would recommend premium, because GM designates it that way."

I learned from the best. Actually, I think GM "recommends" premium for peak performance but says that you can use 87. Earlier model said it was "required". That was later changed to "recommended". I have been using 87 for over three years now on "Robs" recommendation and have noticed no effect on milage or performance. Now those to who would argue, I am sure if I had it on the track in a timed event there would be a difference, but the seat of the pants dyno can't tell. Try it, you may be surprised.

AlBundy
09-01-05, 09:37 PM
When I brought my 96ESC, the dealer I brought it from liked the car so much he started driving it himself. I asked him what type of gas he used and he said mid-grade. So I used mid-grade because I didn't notice any problems with the engine(not that I'm going to use whatever until I get a problem). I got to this forum and it says use premium so I stared using premium. Now in Chi-town the gas is $3.70 a gallon. Do you think I'm not going to go back to mid-grade or even low-grade. I feel kinda stupid for leaving mid-grade anyway.http://www.cadillacforums.com/forums/images/icons/icon8.gif

MWA
09-01-05, 11:56 PM
Ok, Ranger and Al I will give it a try. Thanks for the posts on it. The difference per gallon is not that much yet, though, considering the big picture.

zonie77
09-02-05, 01:19 AM
Computer Controlled Ignition has a knock sensor and a program to adjust timing partially based on the knock sensor.

There will be some differences in similar cars (tolerance stack), and in fuel from different stations on different days, but the only way to answer this question is to try the lower grade fuel in your car and see how it runs.

Also see the effect on your gas mileage from different grades of fuel. You'll have to do some math but you may find you get better gas mileage with the premium and be able to justify the cost difference.

:stirpot:

I don't know in what size steps (degrees) Caddy pulls back the timing but that's part of the problem with giving a clear yes or no. To bad Bb ob isn't around. Maybe someone else knows. In the 90's it was usually 8deg steps.

jsjag
09-02-05, 05:00 PM
I do not have a 1995 owners manual and I was wondering what is the stated the octane rating in the owners manual. On the dash it says premium only. "Premium" varies from State to State. In one State "premium" cound be an octane rating of 90 but in another State "premium" may be an octane rating of 92.

Anybody with a 1995 Deville Concours N* manuall, please let me know the owners manual octane rating.

Thanks

Skotty
09-02-05, 05:02 PM
For as long as I can remember, premium has always been exactly 20 cents more than regular. I live in MO. Is this different in other states?

Cadi is not the only line of cars to require/recommend premium. The Mustang Cobra I owned a few years ago also required premium gas. I always use premium when its required/recommended, given that it is only 20 cents more than regular. The day 20 cents a gallon decides whether I can drive my car or not is the day I know I am really in trouble. But if the difference is closer to a dollar in other areas, then the decision becomes harder.

eldorado1
09-02-05, 07:39 PM
You have a knock sensor. It will retard your timing to prevent damage

That's ASSuming it, the wiring, the connector, etc aren't damaged.

Here's my recommendation, take it or leave it:

If you can predict how you're going to drive for the next week, and you think you're never going to get above above 3000 rpm, get regular. You can save all sorts of money.

IF - IF there is any chance you might need to go pedal-to-the-medal to merge onto highways, or race a honda next to you, do NOT chance it. Get premium. I absolutely hate relying on a knock sensor to retard timing. I really do. The best thing that could happen is you save $5 in gas for the week. The worst thing that could happen is you buy a new engine.

ED's85GT
09-02-05, 09:22 PM
I do not have a 1995 owners manual and I was wondering what is the stated the octane rating in the owners manual. On the dash it says premium only. "Premium" varies from State to State. In one State "premium" cound be an octane rating of 90 but in another State "premium" may be an octane rating of 92.

Anybody with a 1995 Deville Concours N* manuall, please let me know the owners manual octane rating.

Thanks

My '95 Concours manual says:



Fuel
Use premium unleaded gasoline rated at 91 octane or higher. It should
meet specifications ASTM D4814 in the United States and CGSB 3.5-92
in Canada. These fuels should have the propper additives, so you should
not have to add anything to the fuel.

In the United States and Canada, it's easy to be sure you get the right
kind of gasoline (unleaded). You'll see UNLEADED right on the pump.
And only unleaded nozzles will fit into your vehicle's filler neck.

Be sure the posted octane is at least 91. If the octane is less than 91, you
may get a heavy knocking noise when you drive. (In an emergency, you
may be able to use lower octane--as low as 87--if heavy knocking does
not occur.) If you're using 91 or higher octane unleaded gas and you still
get heavy knocking, your engine needs service.



I have been using 89 octane in my 67,XXX mile "95 Concours with no
noticeable adverse effects.

Ed.

wheel-7
09-04-05, 04:59 PM
Ive also started using regular in my 98' Eldorado about three months ago. So far, I have not noticed a difference at all!! No pinging, no loss of gas mileage, no loss of performance that I can tell by the seat of my pants. I dont plan to go back to premium at all.:thumbsup:

IDAMAN
09-08-05, 05:03 PM
Ok, nothing scientific here but...

I was once told by a snooty mechanic who actually tested the octane in the cars which he repaired that...

- In many cases the octane that you think you are buying is actually lower when tested (this all depends on where you buy your gas... i.e. private or corporate owner)

- In one instance I purchased 92 octane regularly and when he tested it he found it to be 84 octane. (wish I knew where I had filled up that day)

- Also, just like a few of you mentioned... I was told that you generally get better mileage on higher octane.

Let us know if anyone gets this figured out for sure... we could all save a buck!
:)

Rick94STS
09-08-05, 06:50 PM
Ive also started using regular in my 98' Eldorado about three months ago. So far, I have not noticed a difference at all!! No pinging, no loss of gas mileage, no loss of performance that I can tell by the seat of my pants. I dont plan to go back to premium at all.:thumbsup:

Same here, I agree with you 100% although I have noticed a puff of smoke comming from the back at first WOT blast.

Mitch3
09-09-05, 02:19 PM
This subject has been approached mucho many times and I was dumb enough to open it again. Because of the prices, I am using regular fuel. Sometimes if I really have cash I will fill up with premium. What's the difference (on my car)? With the regular I sometimes get a hesitation which I never get on premium. This happens going up a hill or from a dead stop, traffic light etc. Bottom line, I do not have a significant drop in performance, so I will continue with regular until the price drops (sure!!! Ha Ha). I have not received a "check engine" message or anything else. As far as difference in mileage. I do find slightly lower mileage with regular but again not significant. NOW HERE IS A QUESTION. Since the price crap has started, has anyone noticed an overall drop in their mileage. I lost about 2 miles per gallon. I'm not talking regular vs premium. I'm talking a general drop in mileage. I was getting about 24.0 per gallon around town. Now I am getting 21.5. Sound liike someone is screwing around with the gas? IS THAT POSSIBLE? I really don't know the answer. A couple of my co workers have noticed the same thing.

eldorado1
09-09-05, 03:05 PM
Sound liike someone is screwing around with the gas? IS THAT POSSIBLE? I really don't know the answer. A couple of my co workers have noticed the same thing.

Yes. More than likely they're cutting the gas with some other (cheaper) additives. Ethanol, toluene, I'm sure there's some others that are cheaper too.

jtauber
09-09-05, 07:29 PM
96 deville 138k mi. ok, i read this thread. the posts and my kids' lecturing about high gas prices and premium gas made me try 89 octane.

pinging on medium hills. back to high test for me.

Mitch3
09-10-05, 08:23 AM
It's Friday, 9/9/05, and gas prices around Albany, NY have dropped. Most stations are charging $3.31 for regular. (+ or - a penny or two). I chuckled at this one though.....the Convenient store at the corner was charging $3.56 when everyone else was around $3.44. Today prices drop to around $3.31 and the Convenient store dropped to $3.19. More game playing.

redseville
09-16-05, 11:17 PM
I only run premium in my '97 when we travel, dealer said to just take her on the interstate a couple of times a month and blow out the carbon as most of her use is in town going to and from work. very happy with the power and smoothness of the N*. Getting 30.98mpg on the interstate and thats with a bad O2 sensor on bank #1. Cheers Mike

davesdeville
09-17-05, 05:52 AM
You must drive hella slow. Blowing out the carbon is a good idea but you can still use regular to do it.

Tombo47
09-17-05, 06:39 PM
If your northstar is 98 and up, you can use regular. However, the early ones are only recommended to be fed premium. The car does not eprform well on regular, my father accidently filled mine with reg and the car was chugging along. It was a horrible expoerience. Expensive car, expensive gas. If you dont weigh in, ya dont wrastle.

eldorado1
09-17-05, 07:46 PM
the ones filled with regular from the factory are '00+. They have modified combustion chambers (which also lowers compression to 10:1) to make 87 octane a possibility. Typically engines that require premium would need to drop 1+ point to run on regular. (So 9.3 in this case) Behold the power of computer designed combustion chambers :)

redseville
09-17-05, 09:22 PM
ask my wife, I definatly dont drive it slowly, that is just what the dealer said, I have been running on 87 unless we are traveling long interstate distances without any problems. I do get just a little bit better mileage on the highway with premium.

94CaddyConcours
09-19-05, 03:19 PM
If your northstar is 98 and up, you can use regular. However, the early ones are only recommended to be fed premium. The car does not eprform well on regular, my father accidently filled mine with reg and the car was chugging along. It was a horrible expoerience. Expensive car, expensive gas. If you dont weigh in, ya dont wrastle.

I CAN TELL IT WAS A HORRIBLE EXPERIENCE BECAUSE YOU SPELL IT EXPOERIENCE. :bouncy:

Ranger
09-19-05, 05:28 PM
If your northstar is 98 and up, you can use regular. However, the early ones are only recommended to be fed premium. The car does not eprform well on regular, my father accidently filled mine with reg and the car was chugging along. It was a horrible expoerience. Expensive car, expensive gas. If you dont weigh in, ya dont wrastle.
2000 on were desined for regular. pre-2000 (Northstars) can and do run well on regular. If yours is not, then something is wrong as you should not be able to tell the difference.

enchanter
09-29-05, 10:14 AM
Throwing in my 2-cents here -- I live in the North Carolina mountains and NEED the full power of my Northstar to pull smoothly over mountains and avoid collisions. I purchase only name-brand premium and have for all my Caddy's (I've owned 6 -- still have the last two) since the early 1980s. The result is far fewer tune-ups -- and for a Northstar that can be costly -- and never a fuel problem. Once, I put a no-name brand (Hotspot) premium in my '82 Seville (yes, she's still going!) with supposedly 92 octane and she got major indigestion. Their "premium" was a fantasy. Never again. If the manual and the gauge says Premium, that's what I do. What are you saving, anyway? A couple of bucks per tank? 'nough said from my corner.

Parrothead
09-29-05, 11:55 AM
The service manager at Crestmont Cadillac in Ohio told me not to use BP fuel, which is Amoco gasoline (at least where I live) He said GM is currently in litigation with them regarding the additives they use. I guess they mess with the injectors. I was not having any problems he just mentioned it in conversation.
anyone else ever hear of this?

mcowden
09-29-05, 12:30 PM
The service manager at Crestmont Cadillac in Ohio told me not to use BP fuel, which is Amoco gasoline (at least where I live) He said GM is currently in litigation with them regarding the additives they use. I guess they mess with the injectors. I was not having any problems he just mentioned it in conversation.
anyone else ever hear of this?

I searched for any evidence of this and found nothing. I wouldn't trust any service manager any further than I could throw him and his wife, kids, house, and cars, all at once. Why he would have something against BP is beyond me, but it could just be a case of the old telephone game. Sounds like an unsubstantiated rumor to me. I use Amoco premium very frequently because it's close to my house. No problems at 96k miles. I'm not saying it's not possible, but it seems pretty unlikely.

ljklaiber
09-29-05, 12:54 PM
Use the fuel the engine was designed for.....or else, just get your less than adequate resale and buy a DaeWoo... The ride is better on the 93.

MUGSANDLUKE
10-02-05, 09:43 PM
Hi Mitch - I have done some extensive research on regular vs premium and i have found that regular should work fine as long as there is no knock or ping. I have a Deville DHS and I switched to regular with no ill effects at all. Mileage actually improved.

mcf1000x2003
10-03-05, 06:53 PM
I was told from a mechanic at the dealership that premium gas was recommended but if i want cheaper gas use the super because regular can ruin your injectors

Ranger
10-03-05, 09:12 PM
Rediculous!

mcowden
10-03-05, 11:08 PM
I was told from a mechanic at the dealership that premium gas was recommended but if i want cheaper gas use the super because regular can ruin your injectors

First piece of advice is to never trust anything anybody tells you at a dealership. Whatever moron told you that has no idea what gasoline or fuel injectors are made of. :stirpot: Lots of people here use regular unleaded all the time and have had zero injector problems. Ranger? Care to chime in here, buddy? :)

I would suggest you never talk to that person again, and any time you get advice from a $tealer$hip, run it up the flagpole here and we'll see if anybody salutes it. I give this one the one-finger salute, and it ain't this finger --> :thumbsup:

Ranger
10-03-05, 11:31 PM
My previous post says it all. Can't think of any politer way to put it.

mcf1000x2003
10-04-05, 03:46 AM
Well even tho he said that I still use Regular because gas prices are just to high right now and i have'nt expierienced any problems with it plus i rather trust people who own the cars rather than someone that is going by the book

mcowden
10-04-05, 10:12 AM
Well even tho he said that I still use Regular because gas prices are just to high right now and i have'nt expierienced any problems with it plus i rather trust people who own the cars rather than someone that is going by the book

Good idea. The funny thing is he's not even going by the book. He's going by rumor, innuendo, bad reasoning, or a runaway imagination. Save yourself the cash. If you're not having any problems with Regular, stick with it. If you are having problems with Regular, something else is wrong.

N0DIH
10-05-05, 11:31 AM
My mom has an 97 Deville 275hp and running 87 in the cool months is ok (Florida), but in the warmer it still pinged. Any ideas on why?

But...
Someone needs to approach the dealers and tell them that you are moving to an area that does not have high octane and what does GM recommend.

In the 1991 4.9L FSM, it has specific instructions to lower timing for 87 octane for areas that do not have it (which I have heard gas companies are pondering the elimination of it due to lack of cars that NEED it, likely bad rumor, but you never know). This is in 1991 FSM Page 6E-C2-17.

I would be surprised if GM doens't have a reflash for lower octane available. Not all countries have the high octane. So that is an idea too, get an export reflash.

Now, and enterprising fellow with might pull the prom (don't tell me you can't, it is called a heat gun to remove, and takes some specific tools, and don't do it unless you know how), read the prom, then send it in to reflash, and then pull it and read it again. Look for changes. Voila, you have just taken your first step into a larger world.... Unless you already have a way to pull the program out via the flash port. Then it is much easier.

peteski
10-06-05, 01:11 AM
There is not need to reflash. The PCM takes care of the timing in real time. That is what the knock sensor is for. It tells PCM to retard timing.

Not sure about OBDII cars, but my OBDI car actually shows what it thinks the fuel octane is (one of the PCM data parameters). So, the timing is set for the specific fuel.

And our ex-resident expert "Rob" confirmed that.

Peteski

N0DIH
10-06-05, 01:22 AM
(deleted a double post)

N0DIH
10-06-05, 01:23 AM
Sorry, I don't buy that. Yes, there IS enough bandwidth in the ECM to pull enough timing out, but the base timing set is too high for 87 octane. Unless the ECM determines that "hey! idiot put in wrong fuel, and I am pulling timing out ALL the time to stop this monster from pinging!" and pulls the average timing map down x degrees, it won't and it will always be running worse than if the timing was set proper for the lower octane.

And that doesn't explain why my mom's car is having ping issues. If that truly were the case, she should never have an issue with pinging.

The issue is when the ECM has to pull out timing to STOP a ping, it takes more timing to stop it than what it took to start it. Say I am at 32 degrees at WOT, and I start to ping, it might take 27 degrees to stop it. BUT, at 31.5 degrees, I won't ping at all, which is better? I have read that it takes around 6 degrees LOWER than ping point to stop the ping and then you are in a pinging timing hysterisis up, ping and down, up, ping and down, and the engine isn't running anywhere near like it should.

Has anyone ever checked with GM on possible software programs? Or does the owners manual specifically state that 87 octane can be used in a region that does not have the required premium fuel?


There is not need to reflash. The PCM takes care of the timing in real time. That is what the knock sensor is for. It tells PCM to retard timing.

Not sure about OBDII cars, but my OBDI car actually shows what it thinks the fuel octane is (one of the PCM data parameters). So, the timing is set for the specific fuel.

And our ex-resident expert "Rob" confirmed that.

Peteski

davesdeville
10-07-05, 02:42 AM
If I run 86 when my car is hot, I can watch the PCM pull timing, the data output is in degrees with tenths and hundredths. Rarely pulls more than a couple degrees, the worst I've seen was 107*F outside, 224* coolant temp, and it pulled 6.5 or so degrees of timing on a WOT.

I do not believe it requires pulling more timing to stop a ping than it does to prevent a ping, what exactly makes you think that in the first place?

If your moms car was an OBDI car I'd tell you to watch PD40 when it's pinging to see if it's even pulling timing at all. Maybe a problem with the knock sensor. But since it's OBDII it might take a scan tool to find the knock sensor based timing retard.

N0DIH
10-07-05, 02:55 AM
She has a 97, so it is OBDII. And she is in Florida and I am in WI. So I can't check into it more on her car, wish I could.

Remember when a ping happens the timing/spark/fuel event starts to become uncontrolled, not stable and consistent. It doesn't just turn on and off. Wish it did. And as we know, every engine is different. Iron head, Al head, big bore, small bore, long stroke, short stroke, etc. The variables are endless. So an engine with a certain shape chamber might stop pinging faster than another, it still takes a certain amount more timing that what it took to start the ping.

What I have read comes from GM training material. I'll see if I can get some time to find it and post about it if there is interest.

N0DIH
10-07-05, 02:57 AM
Can you watch it for pingin and see timing at the same time? Or is it like the 91 4.9L Deville I had?

She has a 97, so it is OBDII. And she is in Florida and I am in WI. So I can't check into it more on her car, wish I could.

Remember when a ping happens the timing/spark/fuel event starts to become uncontrolled, not stable and consistent. It doesn't just turn on and off. Wish it did. And as we know, every engine is different. Iron head, Al head, big bore, small bore, long stroke, short stroke, etc. The variables are endless. So an engine with a certain shape chamber might stop pinging faster than another, it still takes a certain amount more timing that what it took to start the ping.

What I have read comes from GM training material. My mom and dad's old neighbor was the Sr GM instructor at the GM tech school in ST. Louis before they shut it down. He came over and dumped several boxes of books. All GM pubs. You know, if the GM techs actually READ them, they would be awesome mechanics!! But it is very obvious they don't and I am sure the dealers don't send people to Detoit for school either. All costs $$

I'll see if I can get some time to find it and post about it if there is interest.

Something I would love if you would test. What triggers pulling back timing? Temp? If you were to connect a variable resistor to the CTS, and vary it manually while you drove, woudl the timing map go up and down too?


If I run 86 when my car is hot, I can watch the PCM pull timing, the data output is in degrees with tenths and hundredths. Rarely pulls more than a couple degrees, the worst I've seen was 107*F outside, 224* coolant temp, and it pulled 6.5 or so degrees of timing on a WOT.

I do not believe it requires pulling more timing to stop a ping than it does to prevent a ping, what exactly makes you think that in the first place?

If your moms car was an OBDI car I'd tell you to watch PD40 when it's pinging to see if it's even pulling timing at all. Maybe a problem with the knock sensor. But since it's OBDII it might take a scan tool to find the knock sensor based timing retard.

peteski
10-10-05, 01:50 AM
Sorry, I don't buy that. Yes, there IS enough bandwidth in the ECM to pull enough timing out, but the base timing set is too high for 87 octane. Unless the ECM determines that "hey! idiot put in wrong fuel, and I am pulling timing out ALL the time to stop this monster from pinging!" and pulls the average timing map down x degrees, it won't and it will always be running worse than if the timing was set proper for the lower octane.

And that doesn't explain why my mom's car is having ping issues. If that truly were the case, she should never have an issue with pinging.

The issue is when the ECM has to pull out timing to STOP a ping, it takes more timing to stop it than what it took to start it. Say I am at 32 degrees at WOT, and I start to ping, it might take 27 degrees to stop it. BUT, at 31.5 degrees, I won't ping at all, which is better? I have read that it takes around 6 degrees LOWER than ping point to stop the ping and then you are in a pinging timing hysterisis up, ping and down, up, ping and down, and the engine isn't running anywhere near like it should.

Has anyone ever checked with GM on possible software programs? Or does the owners manual specifically state that 87 octane can be used in a region that does not have the required premium fuel?

I'm going here by what "Rob" told us in the past. Too bad that we can't search the forum for his old messages. I think that you were around when he was explaining the way the ping sensor works in conjunction with the PCM.

I don't think that the timing is that dynamic. It will retard the spark for a while (not just for an instant).

As you say, there is only a certain range that the PCM can retard the timing, but it shoudl be enough down to 87 octane gas. If the pinging still persists, there might be another problem with the engine.

I don't have any GM official specs on this and I doubt that is available to the general public (this kind of info is usually proprietary).

But I've been using 87 octane in my OBDI 93 N* Eldorado for a while now and I have no pinging. A bit less power - yes, but no pinging. And the the Calculated Octane Rating PCM parameter is staying on 87. So, the timing is retarded.

Peteski

N0DIH
10-10-05, 02:30 AM
I didn't know there was a COR parameter. Interesting, so there is likely there is not a reflash with that. It does sound like it is taking in the input of how much pinging and estimating octane. That is pretty cool in my book.

So it does sound like Rob was correct in the bandwidth of the system for sure. Being I don't have her car around to look at, I can't see for sure what is up. Is the COR parameter readable from the built in diagnostics? Does it do more than 87 and 92? Like 88, 91, etc? Can it even perk up more if you dump in some 100 octane unleaded race gas? (Don't use avgas, it is lower specific gravity, not the best for low alt, unless you ARE at high alt!)

davesdeville
10-10-05, 04:17 AM
AvGas is leaded anyway.

The calculated octane rating should display 0, 87, 90, or 93. It's PCM output PD42 on OBDI cars. The highest timing curve is setup for 93 (or whatever premium happens to be in your state.)

peteski
10-11-05, 01:54 AM
As Dave stated, the COR parameter is on OBDI cars. Since I don't have OBDII car I can't say of they have it or not. But I'm sure that the OBDII cars handle pinging and timing retardation just as well as the OBDI ones do.

Peteski

1998Deville
11-15-05, 11:32 PM
Ok I know I'm the 'new' guy here but here's my thought.... 20 gallon tank, premium averages around 20 cents more than regular (93 vs 87) (at least here in NW Florida) so that works out to be $4.00 a tank OR LESS depending on if you need 20 gallons.... that's 2 double cheeseburgers and a large coke at McDonalds... so bring lunch once a week :)

krimson_cardnal
11-17-05, 04:24 PM
1998Deville you hit the mark!!

Peace of mind and cutting the fats as well. ;)

robert copeland
11-17-05, 06:58 PM
This subject has been approached mucho many times and I was dumb enough to open it again. Because of the prices, I am using regular fuel. Sometimes if I really have cash I will fill up with premium. What's the difference (on my car)? With the regular I sometimes get a hesitation which I never get on premium. This happens going up a hill or from a dead stop, traffic light etc. Bottom line, I do not have a significant drop in performance, so I will continue with regular until the price drops (sure!!! Ha Ha). I have not received a "check engine" message or anything else. As far as difference in mileage. I do find slightly lower mileage with regular but again not significant. NOW HERE IS A QUESTION. Since the price crap has started, has anyone noticed an overall drop in their mileage. I lost about 2 miles per gallon. I'm not talking regular vs premium. I'm talking a general drop in mileage. I was getting about 24.0 per gallon around town. Now I am getting 21.5. Sound liike someone is screwing around with the gas? IS THAT POSSIBLE? I really don't know the answer. A couple of my co workers have noticed the same thing.
i notice the samething.it seems like the higher the gas prices are the cheaper grade gas it is.i believe they are messing with the fuel.i have heard in mexico the highest grade of fuel is next to kerosene.gas manufacturing plants can probably do that to us.

auroradude
11-18-05, 11:14 AM
I use 93 octane all the time. But one thing, if you use 87 octane..when it uses the knock sensor all the time to throw back timing, doesnt that wear out quicker then? Also does the engine suffer long term performance

mcowden
11-18-05, 11:27 AM
I use 93 octane all the time. But one thing, if you use 87 octane..when it uses the knock sensor all the time to throw back timing, doesnt that wear out quicker then? Also does the engine suffer long term performance

No and no. Knock sensors don't really wear out, and if the sensor indicates timing retardation is needed, the timing is changed and there is no more knock. So it's not like the sensor is going to experience lots of knocking sounds. It's a piezoelectric sensor that is tuned to the frequencies generally created by knocking. It experiences so much noise and vibration in its lifetime that a few short bursts of knocking is not going to hurt anything. I have never heard of a knock sensor going bad. I'm not saying it doesn't happen, but using 87 octane gas isn't going to do it. The engine does not suffer any long-term performance issues from using 87 octane gasoline, despite what people's hunches and gut feelings may say.

dkozloski
11-18-05, 02:26 PM
The test of the spark retard system for some engines is to hook up instrumentation that wll show spark advance and while the engine is running, rap the engine in the area of the knock sensor with a plastic hammer and see if the timing changes.

N0DIH
11-18-05, 03:04 PM
In my 1980 Pontiac book it says to connect a timing light, rev engine to 2000 rpm and then rap on intake manifold (that is where knock sensor is) with a heavy breaker bar. Note timing change. If no change, troubleshoot ESC circuit, if changes, it is ok (assuming it changed enough....)

So anyone can do that, you don't need anything fancy.

peteski
11-20-05, 01:48 PM
That is the nice thing about computer controlled engines: they can adjust to a variety of conditions.

As mentioned above, the knock sensor is a piezoelectric sensor. It is very similar to an old fashion microphone. It doesn't wear out!

I've switched to 87 few months back, my Calculated Octane Parameter shows 87 and my car is as ahppy as ever. I think I feel a bit of a power loss when I step on it, but it is no big deal for me. PCM is doing its job in properly controling my engine.

Peteski

pimpjuice01
11-29-05, 11:19 PM
Ive used gas from many different gas stations and noticed my car runs the best from shell vpower premium, I used to use regular all the time and kinda noticed the idle rough and not running like it should. One day my buddy filled me up with vpower and the car was smoother and better then ever very good take off. I also tried premium from a centex, only 2 in the city and it ran like running regular from there.... I live in Canada drive 93STS..

Also running 20$ premium and 20$ reg get around 130km... was kinda expecting the reg gas to get a bit more KM..........

N0DIH
11-30-05, 01:41 AM
I haven't done any mpg testing on the vpower gas, might be worth a trial for a few months to see if there is anything to the claims from Shell.

Being there are so many variables in mpg testing, I have to keep it to long term to try to see some real results. Temp is the hardest variation, as well as wear.

GreenMachine
11-30-05, 08:45 PM
Strait from my 98' Deville Manual:
"Use premium unleaded gasoline rate at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines but your vechicle may not accelerate as well."

"Be sure the posted octane for premium is at least 91 (at least 89 for middle grade and 87 for regular). If the octane is less tan 87, you get a heavy knocking noise when you drive. If its bad enough, you can damage your engine."

From a 2000 Deville:
"Use premium unleaded rated gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle's acceleration may be slightly reduced.

"Be sure the posted octane for premium is at least 91 (at least 87 for regular). If the octane is less tan 87, you get a heavy knocking noise when you drive. If its bad enough, you can damage your engine."

From a CTS (I know it doesn't have a Northstar but its hear for comparision):
"Use premium unleade gasoline with a posted octane of 91 or higher for best performance. You may also use middle grade or regular unleaded gasline rate at 87 octane or hihger, but your vehicle's acceleration may be slightly reduced. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it is bad enough, it can damage your engine."

Any car you put a higher octane in will in most cases perform better than it would on a lower octane. It will get better fuel economy (sometimes alot better) and will run cooler. Heat is what causes wear (and friction which then causes heat) which could hurt the life of the engine.

I'm not sure I would ever put 87 in really any car unless I lived in an area that only offered 85, 87, 91. 89 is worth the extra for the additives and keeps the engine running cooler and doesn't cost much more than regular.

The world class Northstar was designed for premium, use it to have your engine run they way the creators intended. If you don't mind the loss in performance go with 89. All I know is if i drive a cadillac I never want to hear a ping.

I use mostly 93 in my 98' Deville simply because in the areas I drive the car there isn't any 91 octane availble and I prefer up rather than down. Intresting isn't it that they have, 87, 89, 93 at most places skipping 91 and going to 93 with a markup.

Ranger
11-30-05, 09:36 PM
"Any car you put a higher octane in will in most cases perform better than it would on a lower octane. It will get better fuel economy (sometimes alot better) and will run cooler. Heat is what causes wear (and friction which then causes heat) which could hurt the life of the engine."

Not true, but the oil companies wish they could get everyone to think that way.. Octane is nothing more than an anti knock rating. It does not burn cleaner, cooler, reduce friction, produce more power or increase the life of the engine. It is simply a measure of the fuels ability to resist detonation, nothing more, nothing magic about it. Granted, using regular in a pre 2000 Northstar will cause the PCM to retard the timing a bit and reduce power slightly.

"The world class Northstar was designed for premium, use it to have your engine run they way the creators intended. If you don't mind the loss in performance go with 89. All I know is if i drive a cadillac I never want to hear a ping."

You will not hear any pining with regular. Been there done that. The knock sensor will "hear" it long before you do and compensate for it.

Caddyshack100
11-30-05, 10:30 PM
One of the things about the Caddy Deville is how good on gas it is, I have a 98 deville and I have run it on 94 octane from Sunoco, I get a range of between 690 and 735 km's on a regular basis, the funny thing though, when I switched to 87 octane, the fuel economy stayed above the 700km range, or I think in miles, about 460, and thats having about 9 liters of fuel left in the tank, My car is 85 hwy, and with our cold winter so far, it has only dropped to about 635km with 87 octane, just some thoughts, but what a engine and car,

GreenMachine
12-01-05, 12:33 AM
"Any car you put a higher octane in will in most cases perform better than it would on a lower octane. It will get better fuel economy (sometimes alot better) and will run cooler. Heat is what causes wear (and friction which then causes heat) which could hurt the life of the engine."

Not true, but the oil companies wish they could get everyone to think that way.. Octane is nothing more than an anti knock rating. It does not burn cleaner, cooler, reduce friction, produce more power or increase the life of the engine. It is simply a measure of the fuels ability to resist detonation, nothing more, nothing magic about it. Granted, using regular in a pre 2000 Northstar will cause the PCM to retard the timing a bit and reduce power slightly.

"The world class Northstar was designed for premium, use it to have your engine run they way the creators intended. If you don't mind the loss in performance go with 89. All I know is if i drive a cadillac I never want to hear a ping."

You will not hear any pining with regular. Been there done that. The knock sensor will "hear" it long before you do and compensate for it.

Car and driver did an article on the performance of several cars with higher octane and with regular fuels to see if it did make a differance. Faster timeings mean better performance, not more power but the same power more often. Heres the article: http://www.caranddriver.com/article.asp?section_id=4&article_id=3604&page_number=2

Also there is a differance in the detergant "cocktail" between the 3 grades of gas, premium fuel has more regular has less, cleans the engine differantly. I have an article on that saved somewhere but I can't find it.

Now I'm not saying if you have a regular gasoline car to dive into the premium, I'm just saying if you have the extra money and want to keep that engine cleaner use middlegrade. What I can't see is putting 85 or 87 in a Cadillac (whatever year it may be) when 89 is availble and when you want true northstar performance go with the 91/93.

N0DIH
12-01-05, 02:56 PM
How many people here have a N* and have tried to use 87 octane AND have had pinging problems? What engine do you have? 275hp or 300hp?
.
.
My mom and dad did (97 N* 275hp. they were buying gas at cheapest station around. I recommended that they try again, stepping down octane from 92 to 89 to 87 gradually as no pinging occurs. BUT keep a consistent station for a while.
They did report pinging with 87 and it scared them back to 92. It was Florida in 80+ weather.

thu
12-01-05, 03:43 PM
I haven't had my STS long enough to tell if the different grades result in different MPG figures.

However, I have used regular unleaded in my 93 Deville, which specifies 'Premimum Unleaded Fuel Only' for almost 300,000 miles with no ill effects. I have *never* heard it knock. Switching to premium resulted in zero MPG gain.

However, living between 6200 and 7200 ft elevation has something to do with it. :)

N0DIH
12-03-05, 11:06 PM
Yes, altitude has a little to do with it... For ever 1000 foot altitude increase, you reduce your octane requirement by 1 point. Hence why my 1980 Turbo T/A with a 70 455 Pontiac with 10:1 compression ran just fine when I was in Colorado Springs.

Here in SE WI, we are around 700 feet. So not much help there.... But my 94 Fleetwood with the LT1 and 10:1 compression runs fine on GM specified 87 octane. I am however, doing some of my fuel economy experiements on the VPower gas now to see if it really helps any.


I haven't had my STS long enough to tell if the different grades result in different MPG figures.

However, I have used regular unleaded in my 93 Deville, which specifies 'Premimum Unleaded Fuel Only' for almost 300,000 miles with no ill effects. I have *never* heard it knock. Switching to premium resulted in zero MPG gain.

However, living between 6200 and 7200 ft elevation has something to do with it. :)

mtflight
12-05-05, 12:10 AM
How many people here have a N* and have tried to use 87 octane AND have had pinging problems? What engine do you have? 275hp or 300hp?
.
.
My mom and dad did (97 N* 275hp. they were buying gas at cheapest station around. I recommended that they try again, stepping down octane from 92 to 89 to 87 gradually as no pinging occurs. BUT keep a consistent station for a while.
They did report pinging with 87 and it scared them back to 92. It was Florida in 80+ weather.

After Katrina, I filled with regular for a few tanks and then mixed in some premium and regular. Passenger noted pinging--I thought "you're crazy because... Northstar...knock sensor... retard timing... no pinging...etc" Then I flogged it going up a slight incline on the highway... and sure enough--pinging.

Maybe it was bad gas, but I have stuck with premium ever since.

peteski
12-05-05, 02:58 AM
I think that I already mentioned this on this thread. I have a 93 N* 295hp and have been running regular (87) gas in it for several months now. No pinging. Maybe slight loss of power.
My calculated octane parameter in the ECM shows 87octane. All is well...
Car has over 120k miles.

Peteski

AlBundy
12-06-05, 09:05 PM
I use regular in my 275hp 96, no pinging. I notice the MPG fell-off but only because I was monitering it(because of threads like this one), other than that I don't think I would have noticed.

GreenMachine
12-06-05, 10:20 PM
I think that I already mentioned this on this thread. I have a 93 N* 295hp and have been running regular (87) gas in it for several months now. No pinging. Maybe slight loss of power.
My calculated octane parameter in the ECM shows 87octane. All is well...
Car has over 120k miles.

Peteski

How do you check the octane paremeter in the ECM? Kinda a nice feature to find out if you get what you pay for.

mcowden
12-06-05, 11:40 PM
How do you check the octane paremeter in the ECM? Kinda a nice feature to find out if you get what you pay for.

On an OBD-II car (1996 or newer), you can't do it. Only 1995 or older cars can see the parameter.

GreenMachine
12-06-05, 11:42 PM
On an OBD-II car (1996 or newer), you can't do it. Only 1995 or older cars can see the parameter.
Thanks for info, intresting to know. Wonder why they removed that.

peteski
12-08-05, 03:54 AM
Yes, OBD I cars only. PCM Data Parameter P0042.
It doesn't actually sample the gasoline. it makes an educated guess based on many parameters (I'm sure that knock detector is one of them). So I suspect that if the car is in a need of a tuneup or unsound mechanically, that parameter will not show a true value.

Peteski

N0DIH
01-22-06, 02:14 AM
I talked to my dad and they recently filled up the 97 with 87 octane for a short trip and they feel it is running just fine with it. My mom said she thinks it might ping once when she makes a rapid stab at the gas pedal, else, it is quiet. So at least they can save some $$ on that....

Thanks guys!

Swine
01-22-06, 02:47 AM
Car and driver did an article on the performance of several cars with higher octane and with regular fuels to see if it did make a differance. Faster timeings mean better performance, not more power but the same power more often. Heres the article: http://www.caranddriver.com/article.asp?section_id=4&article_id=3604&page_number=2

Also there is a differance in the detergant "cocktail" between the 3 grades of gas, premium fuel has more regular has less, cleans the engine differantly. I have an article on that saved somewhere but I can't find it.

Now I'm not saying if you have a regular gasoline car to dive into the premium, I'm just saying if you have the extra money and want to keep that engine cleaner use middlegrade. What I can't see is putting 85 or 87 in a Cadillac (whatever year it may be) when 89 is availble and when you want true northstar performance go with the 91/93.Wondering if you read the article you linked...
The Accord took a tiny step backward in power (minus 2.6 percent) and performance (minus 1.5 percent) on premium fuel, a phenomenon for which none of the experts we consulted could offer an explanation except to posit that the results may fall within normal test-to-test variability.

The results were more dramatic with the test cars that require premium fuel.

No discernable difference in cars that do not require premium. Gains and losses with margin for error, in both directions...

If your car is rated for 87 octane, you gain nothing by running premium.

If your car requires 92+, you need to run the good stuff...

Night Wolf
01-22-06, 03:48 AM
I didn't read all the replies... but one thing I read early on...

simply saying "my car dosn't ping on 87, so I use it" does NO good at all on the Northstar or most any modern engine... they have knock sensors to prevent ping by retarding the timing... so how in the world can you base something off hearing, if it isn't there in the first place?

That being said, *IF* I owned a Northstar it would get premium.

My 4.9 gets premium. No knock sensor, plus the timing has been advanced... either way it requires premium, it gets premium for the whole $2 difference per fill up, it isn' worth using regular.

my 1989 Oldsmobile Eighty Eight has a 3800 V6, that says regular 87 is fine... for awhile I ran 93 in then I started, and have been for a long time running 87.... on that engine, the premium didn't make a difference, it probably runs better on 87 anyway. It also has a knock sensor, but I know it had no problem with 87.

my '79 DeVille with the 425, again, I used to run premium in that, now she gets regular as well... took a little while for me to accept that.. but truth is, with 8.2:1 compression I could probably piss in the tank and it'll run :)

N0DIH
01-22-06, 10:02 AM
With GM cars, i am not surprised. When wait4meperformance and I went over my tune on the 96 Burb, he revised the timing and fuel tables to USE 93 octane, to improve power. GM has not spent much time on these tables optimizing them for power and economy. It is just amazing that the hardware is there, but the software wasn't. This is a 1996 truck. No possibilty with it to do anything different on any octane above 83 or so. Very poor timing. Once he made his changes (wonder changes!) the truck is very diifferent, and a dream to drive. I am getting 1-2 mpg bettter city.

EDIT: It will run now on 87 or 93, but is now allowed to adapt to 93, where before it was limited to not adapt at all. Thanks GM, we appreciate it....

So likely Honda allowed it to do it, and the rest were not so inclined to allow for power improvements based on octane.

As for cars that require premium like the N*, thise routines are likely revised and made alive. They just put the same #'s in all fields. Anyone could have come up with better!!



Wondering if you read the article you linked...

No discernable difference in cars that do not require premium. Gains and losses with margin for error, in both directions...

If your car is rated for 87 octane, you gain nothing by running premium.

If your car requires 92+, you need to run the good stuff...

caddysteve
01-27-06, 09:19 PM
Hi everyone.I am new to the forum, so i am not an "expert", but i have been running my car on 87 octane for well over seven years with no ill effects.This car is as strong as the day i bought it.Have fun with the old girl.cheers mate!

therodman
01-28-06, 01:42 PM
I just checked my parameter code for fuel octane and it said 87 which is what I've been using since I read about this issue on this board maybe a year ago. I've never heard a ping or noticed a loss of mileage since using the 87, runs just fine.