: Myth!!!!! Octane 99 and prior VS 00+



AJxtcman
08-11-07, 11:09 AM
This may get moved to tech tips, but I think it needs to be here.
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99 information first. Big Myth!
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Octane Description
Octane is a measure of a fuel's ability to resist spark knock. Spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock. In a case such as this, poor engine performance and reduced fuel economy could result. Also, in severe knock cases, engine damage may occur.

Knock Sensor (KS) System Description
Varying octane levels in gasoline can cause detonation in high performance engines. Detonation is sometimes called spark knock. Spark knock causes the pistons and rings to vibrate and rattle producing the spark knocking sound.

To control spark knock a Knock Sensor (KS) is used. This system is designed to retard spark timing to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and to improve fuel economy.

The Knock Sensor (KS) system has two major components:

The KS module.
The Knock Sensor (KS).
The knock sensor is mounted into the engine block under the intake manifold. The knock sensor produces an AC voltage which increases with the severity of the knock. This signal voltage inputs to the Powertrain Control Module (PCM). The PCM then adjusts the Ignition Control (IC) to reduce spark knocking.

This powertrain system runs several tests of the Knock Sensor system. A fault in the KS system will PCM DTCs P0325 will detect KS Module or PCM faults, P0326 will detect low octane fuel or engine noise and P0326 will detect Knock Sensor and/or circuit faults.

Fuel Specifications
Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle 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 than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine.

If you're using fuel rated at the recommended octane or higher and you hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or driving up a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem.
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On the Tech II it shows Octane Level and the PCM adjust for it!!!!

msta293412
08-11-07, 11:16 AM
So my 2001 STS, witch is designed to run good on 87 octane, will run better with 93 octane?.....are you sure?

AJxtcman
08-11-07, 11:38 AM
So my 2001 STS, witch is designed to run good on 87 octane, will run better with 93 octane?.....are you sure?

My Computer stopped responding. I had all the 2000+ and was adding the pictures. I opened the Task Manager and found a program running for Programing PCM's. I opened it last night and it did not close.
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I will reload the info now.

msta293412
08-11-07, 11:41 AM
Definetly let me know....

AJxtcman
08-11-07, 11:47 AM
2000+ GM SERVICE INFORMATION FROM GM & FSM.
.
Octane description
Octane is a measure of a fuel's ability to resist spark knock. Spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock. In a case such as this, poor engine performance and reduced fuel economy could result. Also, in severe knock cases, engine damage may occur.

Knock Sensor (KS) System
Purpose
Varying octane levels in todays gasoline may cause detonation in some engines. Detonation is caused by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of two or more opposing pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation could result in engine damage. To control spark knock, a knock sensor (KS) system is used. This system is designed to retard spark timing when spark knock is detected in the engine. The KS system allows the engine to use maximum spark advance for optimal driveability and fuel economy.

Operation
The PCM uses a knock sensor (KS) to detect abnormal vibration in the engine (detonation/spark knocking). Mounted in the engine block, under the intake manifold, the knock sensor produces an AC signal at all engine speeds and loads. The PCM then adjusts the spark timing based on the amplitude and frequency of the KS signal.

A knock sensor module is no longer used to diagnose the knock sensor system. The circuitry is integrated into the PCM. The PCM uses the knock sensor signal to calculate an average voltage. Then, the PCM assigns a voltage range above and below the average voltage value. The PCM checks the knock sensor and related wiring by comparing the actual knock signal to the assigned voltage range. A normal knock sensor signal should vary outside the assigned voltage range (as shown in the normal knock sensor figure). If PCM detects a signal voltage within the assigned voltage range, DTC P0327 will set (as shown in the abnormal knock sensor figure).

34141
(1) Upper Fail Region
(2) Knock Sensor Calculated Average
(3) Knock Sensor Signal (Normal)
(4) Lower Fail Region


34142
(1) Upper Fail Region
(2) Knock Sensor Calculated Average
(3) Knock Sensor Signal (Failed)
(4) Lower Fail Region

Diagnosis
If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.

DTC P0327 is designed to diagnose the knock sensors, and related wiring. Problems encountered with the KS system should set a DTC. However, refer to Detonation/Spark Knock in Symptoms if no DTC sets, and the customers complaint of detonation points to the KS system.

Fuel Specifications
Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle 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 than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine.

If you're using fuel rated at the recommended octane or higher and you hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or driving up a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem.

AJxtcman
08-11-07, 11:53 AM
You can run lower octane in the 99 and prior just like a 00+.

00+ Compression Ratio 10.0:1
99 Compression Ratio 10.3:1

.3 is not going to make the differnce that everyone states. The PCM has the ability to adjust for the Octane level and has since 96 or even before that. If the 99 had to have Premium and the 00 did not it would have been in the PCM program and I just don't see that it is not in the 99 program.

danbuc
08-13-07, 02:10 AM
Yeah, we all know you can run regular in the '99 and prior year cars....many people here do, and have for years....I don't because I like having the maximum level of power on tap at all times.....retarded timing is for losers...

3rd Coast Balla
08-13-07, 02:34 AM
but isnt better octane gas better for ur car, like against sludge buildup in the engine..whutever the case i still use supreme...come one its a cadillac not a honda.

AJxtcman
08-13-07, 07:52 AM
but isnt better octane gas better for ur car, like against sludge buildup in the engine..whutever the case i still use supreme...come one its a cadillac not a honda.

Actually Premium will cause more combustion chamber deposits.
Top tier maybe an exception to that.

AJxtcman
08-13-07, 07:58 AM
Yeah, we all know you can run regular in the '99 and prior year cars....many people here do, and have for years....I don't because I like having the maximum level of power on tap at all times.....retarded timing is for losers...

I see it in threads all the time.
My 00+ can run regular because they changed the compression ratio.
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You must not understand the timing of a Northstar because it retards it constanly as you drive. It runs up and down.

msta293412
08-13-07, 09:31 AM
No wonder, I seem to see performance improvement when I run 93....I thought iot was in my head, beacause I usually run 87....some one told me running 93 would hurt performance because , my timing was set for 87.....silly I guess, now that I understand the pcm adjusts for octane, temp, etc...

jadcock
08-13-07, 09:35 AM
My '97 couldn't even run midgrade without a noticeable performance lag. Throttle response was very soft, even on midgrade. It definitely ran the best on premium.

My '01 has never seen anything but regular, and it runs fantastic on regular. It may run even better on premium, I don't know.

Zorb750
08-14-07, 02:10 AM
I see it in threads all the time.
...
You must not understand the timing of a Northstar because it retards it constanly as you drive. It runs up and down.

Duh. All engines do. Retard timing = smoother operation. Timing turns back when power is not needed, and the ratio of throttle position to RPM remains static for a long time. The point is that with lower octane fuel it will retard it more. This has a noticable effect on city mileage in my experience. highway doesn't change as much, but in stop and go traffic, the higher octane fuel makes a big difference.

msta293412
08-14-07, 08:52 AM
I have been running 93 since the beginning of this thread.....and I do notice a improvement of overall performance over running 87.......GRAET.....I dont care about $, Im gonna use 93 from now on!

wydopnthrtl
08-14-07, 12:08 PM
I've data logged my 01 eldo for WOT timing on 87, 93, 94, & 97 octanes. (running the tank nearly dry each time to help insure an accurate rating)
My timing max's out at 31BTDC no matter what fuel is used. The O2's read the same as well.

However I have seen a repeatable 2-ish mpg difference in using 87 vs 93. So I'd conclude that at WOT there is not a difference (on my 01) but at part throttle there is. (There is just no way to get a accurate comparison at part throttle because of operatng conditions and throttle angle)

btw, If any of you guys can see your timing live. It's amazing to watch! Just putting around town at 30-40mpg I've seen it go over 50btdc. No other car I've read does that.

Rich

msta293412
08-14-07, 12:18 PM
You just burst my bubble.......I thought 93 would cause the pcm to advance timing a bit over 87......I swear I feel a difference though......

AJxtcman
08-14-07, 12:36 PM
You just burst my bubble.......I thought 93 would cause the pcm to advance timing a bit over 87......I swear I feel a difference though......

It does
WOT is a different chart. I will see if I can get a screen shot

jadcock
08-14-07, 01:59 PM
When you guys are saying there is a MPG difference between regular and premium, you mean in favor of premium right? Meaning slightly better MPG when using premium?

Ranger
08-14-07, 04:04 PM
If there is any difference, it would be an improvement with premium. That said, I am sure if you run the numbers, the 2 MPG mentioned is not worth the extra cost.

AJxtcman
08-14-07, 05:48 PM
If there is any difference, it would be an improvement with premium. That said, I am sure if you run the numbers, the 2 MPG mentioned is not worth the extra cost.


When you guys are saying there is a MPG difference between regular and premium, you mean in favor of premium right? Meaning slightly better MPG when using premium?

The mileage could be worse for two reasons. The first is it runs better so your foot is in it more. The second would be a non top tier premium fuel. If it is not top tier it may have volatile additive that may cause more fuel consumption. If it has more alki it take more fuel or it will be lean. That is a fact.

wydopnthrtl
08-15-07, 09:47 AM
I'm not that familiar with cadillac tuning. But I do see a repeatable increase in milage running higher octane. So the PCM has to be adjusting timing and fuel for it in some way.

I can only assume it's based on knock sensor readings?

For example.. two months ago we went to Memphis for the BBQ contest. A few tanks before the trip and on the way down I ran nothing but 87octane. Used 93 octane on the way back (low fuel light coming on before filling with 93). We were running the same roads, same speeds, and same driving style. Going down we averaged 26.9mpg and on the way back we averaged 29.0 This is about the same type of difference I see running locally here in SE Mich.

Seat of the pants... I can't tell any difference. And at WOT I can't measure any difference either. But something is indeed changing at part throttle operation.

Rich

jadcock
08-15-07, 02:19 PM
If there is any difference, it would be an improvement with premium. That said, I am sure if you run the numbers, the 2 MPG mentioned is not worth the extra cost.

Boy, 2 MPG would sure make it worth it for me.

On regular, I'm running about 18-19 MPG. At a cost of $2.60/gallon, and about 500 miles per month, that's 26-28 gallons per month, or $68-73 per month.

On premium, assume I get 20-21 MPG. At a cost of $2.80/gallon, and still about 500 miles per month, that's 24-25 gallons per month, or $67-70 per month.

If the only change to the car when running premium is 10% better economy and a few more horsies, the numbers are definitely in favor of premium, because right now, premium is LESS than 10% more expensive than regular. As long as the mileage improvement is within the price difference between regular and premium (% wise), it's a no-brainer for me.

Now, only to find out if I'll see that kind of % change. I'll run a few tanks and keep track.

Ranger
08-15-07, 06:11 PM
OK, I guess in your case you'd save about $2.00/month. I am guessing by your mileage, you're doing mostly city driving? I'm guessing that highway would be less effective.

AJxtcman
08-15-07, 07:18 PM
Top Tier
If it is not Top Tier you could get a blend that has a higher octane rating, but it takes more fuel to run. We actually see this. We had a guy with a CTS V come in last year. He had just filled up. His tank was almost empty I mean DRY. He filled it up with Premium and got about 1 block. He had it towed to us. The car would run, but it was so lean it would backfire and stall if you touched the gas pedal. I helped the guy out that was working on it and we borrowed an E85 tester. 98% alcohol. The car sat for two week before the transport company paid the bill. The gas station had just got the Premium tank filled about 1/2 hour before. The Tanker company said that they could not have done this. This was not a Top Tier station and the premium at that station is regular with more alcohol. That came from the Tanker company guy that came out and got fuel samples.

jadcock
08-16-07, 08:19 AM
OK, I guess in your case you'd save about $2.00/month. I am guessing by your mileage, you're doing mostly city driving? I'm guessing that highway would be less effective.

Yes, that's mostly city driving, but some expressway. Highway mileage is around 25-26 for me. I don't even care about "saving" money -- as long as I break even, it'd be worth it for me. Who wouldn't pay the same per month to have 5 more horsepower, or whatever premium might bring? :thumbsup:

Personally, I don't think I'll see a 10% increase in fuel economy. But I'll never know until I try it.

We were always told that the 2000+ engines were optimized for regular, so using premium wouldn't help. Maybe that's not 100% accurate.

AJxtcman
08-16-07, 02:14 PM
I was looking up some facts today and found some more information
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As posted below from the FSM for 00+
This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock
.
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As posted at the media.gm. site.
2000 DeVille Product Information
Recommended fuel---- 87 octane unleaded regular
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Hmmm.

danbuc
08-16-07, 11:47 PM
I see it in threads all the time.
My 00+ can run regular because they changed the compression ratio.
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You must not understand the timing of a Northstar because it retards it constanly as you drive. It runs up and down.


No, I understand it just fine.....but I'd rather not have it retarded throughout the entire RPM range, or lower than normal if I don't have too. That's why I use Premium. Why make the ignition system have to compensate for the lower octane rating if I don't have too. No sense loosing power, albeit a minute amount to save a couple bucks. When I put my foot into the headlights...I want every ounce of power that could possibly be available. I do this often, which is why I spend the extra couple bucks on premium.

AJxtcman
08-17-07, 07:25 AM
danbuc I see you have a 98 listed. If you can run a 00+ on 87 octane you can run a 96 to 99 on 87 octane. At 10 to 1 plus you should have 93 octane. I think the car will have diminished performance no matter what year. I run 93 in the rocket. With the weight of the car it may run the same on 89.
The way I look at it is that they are all the same as far as fuel needs. The computer can adjust for it.
Do you know anything about E85 detection in E85 Vehicles?
GM has two types of percentage detection. The main one is a sensor in the fuel delivery line. The second one I do not remember this second.
Mopar uses a simulated detection program. A company has run every percentage of alcohol and every load condition on an engine. The engine management sensors (Mainly O2, mass and knock) change with load and alcohol. This mean the program can adjust constantly for any blend of E85. GM may go to this Third party program that is embedded into a chip on the board. I am not sure why they have not yet. I have been told currently after you reprogram a PCM in an E85 GM truck it will not run if it has E85 in the tank. You have to make it run on gas and then switch it over to the fuel in the tank. E85 makes more horse power, but uses more fuel. Now this has been on newer PCM's but they work very fast to compensate.

Dooman
08-17-07, 09:38 AM
I've had my 99 since October 2000. I can tell EVERY tank my wife filled up with 87 as compared to 93/94 that I put in. Mid throttle around town is exactly the spot you can feel it. Seems to need more pedal push to increase speed. I'd pass a test any day if it was to see which gas we had in it.
Not worth the money they may say? LOL Neither was the car!

AJxtcman
08-17-07, 10:31 AM
I've had my 99 since October 2000. I can tell EVERY tank my wife filled up with 87 as compared to 93/94 that I put in. Mid throttle around town is exactly the spot you can feel it. Seems to need more pedal push to increase speed. I'd pass a test any day if it was to see which gas we had in it.
Not worth the money they may say? LOL Neither was the car!

Thanks for the input. That would be how I see the program working. Mid to low RPM and mid throttle.

jadcock
08-17-07, 11:05 AM
That was the way my '97 performed (lack of mid-range throttle response). I've always ran the '01 on regular, but maybe I don't know what I'm missing. I'm definitely going to try premium on the next tank and see what difference that makes.

Ranger
08-17-07, 12:09 PM
When I switched my '97 from premium to regular I swear I saw no difference in performance or mileage. Maybe my ass is just not that sensitive or I too don't know what I should be looking for. Then again, I do not push it very hard, very often. Only an occasional (therapeutic) WOT.

AlBundy
08-17-07, 07:33 PM
Remember this:
http://www.hotrod.com/techarticles/engine/fuel_octane_rating_comparison/index.html

Ranger
08-17-07, 08:24 PM
So much for the "good stuff". Pretty much confirms what I have been saying. Thanks Al.

AlBundy
08-17-07, 08:37 PM
So much for the "good stuff". Pretty much confirms what I have been saying. Thanks Al.

No problem.:thumbsup: Good article. Someone posted it earlier this year.

jadcock
08-30-07, 09:56 PM
For what it's worth...

I just ran through my first tank of premium fuel (actually, about 80% premium, 20% regular). Unfortunately, I had been keeping tank-by-tank MPG records for only the three tanks prior, but my cost/mile was consistent (either 15 or 16 cents/mile). It's turned out that for the first tank of premium, I have broken exactly even in MPG gain and cost gain with the premium fuel. I was at exactly 15 cents/mile again this tank. I consider that a 'win', because I can feel as big of a difference in how this '01 runs as I did in the '97.

AJxtcman
08-30-07, 10:26 PM
For what it's worth...

I just ran through my first tank of premium fuel (actually, about 80% premium, 20% regular). Unfortunately, I had been keeping tank-by-tank MPG records for only the three tanks prior, but my cost/mile was consistent (either 15 or 16 cents/mile). It's turned out that for the first tank of premium, I have broken exactly even in MPG gain and cost gain with the premium fuel. I was at exactly 15 cents/mile again this tank. I consider that a 'win', because I can feel as big of a difference in how this '01 runs as I did in the '97.

Thank you are #1 today

Submariner409
08-30-07, 11:10 PM
:annoyed: Up in the Seville forum I just posted a rant and rave about ethanol, MTBE, octane, and performance. Here's my take: If I (and a few others) are headed out to the country for some car driving fun, I fill up with 93 Texaco. Tooling around like an old fart, doctors, whatever, I run Texaco/Shell/Chevron/dog snot 87. The STS loves it all. Subjectively I feel a slight performance boost with 93, but not enough to keep it in the tank all the time. Fortunately, the modern N* management system would probably digest Wesson Oil and diesel, too. On the other hand, I would hesitate at doses of nitromethane or ether.

AlBundy
08-30-07, 11:13 PM
I think a merge might be necessary.

jadcock
09-01-07, 09:47 AM
Subjectively I feel a slight performance boost with 93, but not enough to keep it in the tank all the time.

If your cost/mile works out, why not use 93 all the time? That's why I started tracking it in the first place. As near as I can tell, with the same drive cycle (all I use my car for is mostly back and forth to work), I'm getting the exact same cost/mile (15 cents) when using premium. So for me, it's a no-brainer. As long as it's within a few cents of using regular, the improvement I get is worth it. Again, I'm not claiming 1/2 second in the 1/4 mile here. I'm talking about low and mid range throttle response, overall smoothness during throttle transitions, etc. The use of premium has given it a "snap" when driving around town than it didn't have with regular.

jadcock
09-01-07, 09:49 AM
I think a merge might be necessary.

I agree.

cadillacmike68
09-02-07, 02:29 AM
Mighty interesting. I can read the self contradictions right out of the manuals, and know about the PCM and knock sensors being able to retard timing to prevent knock, but it's still enlightening.

So, what is a top tier fuel? Hess, Mobil/Exxon, Chevron, Shell, etc as opposed to racetrack marathon and the other "brand x" gas stations?

I'm doing trips next weekend and the one after. I'll track MPG, etc.

Thanks AJ

You have a NorthStar shoveled into a fiero??? I had an 84 fiero- spun it into the snowbanks twice in Mass.

jadcock
09-02-07, 08:05 AM
http://www.toptiergas.com/

That's the link to Top Tier gas. Many brands say that they meet the Top Tier standard, even though they are not listed. ExxonMobil for example:

http://www.usatoday.com/money/industries/energy/2007-06-13-bad-gas-usat_N.htm

fleishman
09-04-07, 06:32 PM
In reply to the top tier list, We have a texaco station here in maine, and it is the worst gas, no local that knows whats what will put it in their cars.

Does anyone know who supplies Sams Club with their fuel? Speaking of $/gallon, as a member I get 5 cents off per gallon.

What sensors in the engine, other than o2 sensors, control how rich or lean your engine runs?

clarkz71
09-07-07, 01:38 PM
So much for the "good stuff". Pretty much confirms what I have been saying. Thanks Al.

I don't think so, the 91 made 6.1 more hp & 8.1 more lb ft of torque then 87.

87-Octane Unleaded: 396.0 hp/401.3 lb-ft

91-Octane Unleaded: 402.1 hp/409.4 lb-ft

And I also have conformed an increase of 2.5 mpg with premium over regular.

Ranger
09-07-07, 07:47 PM
But do you really think that you can tell the difference between 6.1 more HP or 8.1 lb/ft of torque?

clarkz71
09-12-07, 09:08 AM
Yes, as a matter of fact I can. From my years of dyno tuning sport bikes
I could make a jet change or cam timing adjustment and feel the difference
of 3 or 4 hp. The fastchip I put in my Eldo is only rated for 12 hp and I
definitly can feel that.

AJxtcman
11-15-10, 01:00 PM
2000+ GM SERVICE INFORMATION FROM GM & FSM.
.
Octane description
Octane is a measure of a fuel's ability to resist spark knock. Spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock. In a case such as this, poor engine performance and reduced fuel economy could result. Also, in severe knock cases, engine damage may occur.

Knock Sensor (KS) System
Purpose
Varying octane levels in todays gasoline may cause detonation in some engines. Detonation is caused by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of two or more opposing pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation could result in engine damage. To control spark knock, a knock sensor (KS) system is used. This system is designed to retard spark timing when spark knock is detected in the engine. The KS system allows the engine to use maximum spark advance for optimal driveability and fuel economy.

Operation
The PCM uses a knock sensor (KS) to detect abnormal vibration in the engine (detonation/spark knocking). Mounted in the engine block, under the intake manifold, the knock sensor produces an AC signal at all engine speeds and loads. The PCM then adjusts the spark timing based on the amplitude and frequency of the KS signal.

A knock sensor module is no longer used to diagnose the knock sensor system. The circuitry is integrated into the PCM. The PCM uses the knock sensor signal to calculate an average voltage. Then, the PCM assigns a voltage range above and below the average voltage value. The PCM checks the knock sensor and related wiring by comparing the actual knock signal to the assigned voltage range. A normal knock sensor signal should vary outside the assigned voltage range (as shown in the normal knock sensor figure). If PCM detects a signal voltage within the assigned voltage range, DTC P0327 will set (as shown in the abnormal knock sensor figure).

34141
(1) Upper Fail Region
(2) Knock Sensor Calculated Average
(3) Knock Sensor Signal (Normal)
(4) Lower Fail Region


34142
(1) Upper Fail Region
(2) Knock Sensor Calculated Average
(3) Knock Sensor Signal (Failed)
(4) Lower Fail Region

Diagnosis
If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.

DTC P0327 is designed to diagnose the knock sensors, and related wiring. Problems encountered with the KS system should set a DTC. However, refer to Detonation/Spark Knock in Symptoms if no DTC sets, and the customers complaint of detonation points to the KS system.

Fuel Specifications
Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle 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 than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine.

If you're using fuel rated at the recommended octane or higher and you hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or driving up a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem.

http://i224.photobucket.com/albums/dd25/AJxtcman/Northstar/Fuel.jpg

AJxtcman
11-15-10, 01:02 PM
I have some additional info to post, but it will have to wait

Submariner409
11-15-10, 02:35 PM
As I posted up in the Northstar engine swap thread, "Why does the 2002 Seville Owner's Manual recommend 87 octane fuel for everyday use ?"

Page 6-3.

..............and before anyone hangs their hat on anything in the last 3 posts (this has been resurrected from 2007), I suggest you go back to Post #1 and start reading all the way to here to decipher the flip-flops and discussions concerning engines, years, and octanes. In some cases an explanation, documentation, or opinion for one post is changed considerably in others - Caveat emptor.

.............will someone with a 2000 Northstar car Owner's Manual please quote the fuel recommendation contained in the chapter titled something like "Service and Appearance Care" - Fuel ?

AJxtcman
11-15-10, 04:29 PM
2002 Seville GM Service Information (SI)
http://i224.photobucket.com/albums/dd25/AJxtcman/Northstar/2002SI.jpg


2003 Seville Owners Manual
http://i224.photobucket.com/albums/dd25/AJxtcman/Northstar/2003KY.jpg

Ranger
11-15-10, 04:45 PM
Yes, as a matter of fact I can. From my years of dyno tuning sport bikes
I could make a jet change or cam timing adjustment and feel the difference
of 3 or 4 hp. The fastchip I put in my Eldo is only rated for 12 hp and I
definitly can feel that.
But I wonder if you where given 5 identical cars to drive and SOMEONE ELSE put a "fast chip" in one of them, could you pick out the one with 12 more HP. I seriously doubt anyone's ass dyno is THAT sensitive.

Submariner409
11-15-10, 04:47 PM
Thanks, AJ ----------I was pretty sure I hadn't quite lost my mind..........

Just like everything else from the first FWD 4.6 Northstar to mid-2004, there are significant differences from most years to most years, so there's no "one size fits all" when someone is dealing with recommendations and repairs..............

97EldoCoupe
11-15-10, 10:47 PM
As for E85 - I will never fill up my truck with that stuff again - $0.40 per gallon saved, but milage dropped from 18.9 MPG highway running at 85 MPH to 10.0 MPG I did notice it seemed to have good power on that fuel, not sure if it was any more than on 87 octane.....

I agree with AJ. Anything with 10.0:1 + compression should be running premium- 93+. Sunoco here in Canada sells 94 octane- not sure how accuate the numbers are. But for this reason I like the pumps in the US of A - usually American pumps have a separate hose/nozzle for each grade of fuel. Here in Canada it's one friggin hose for all three grades. If I'm filling in a tank of premium, I don't want a 10', 3/4 I.D. hose full of regular fuel that I just paid premium prices for. Depends on what the last guy filled in. It really ticks me off.