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2003 Deville
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Discussion Starter #1
2003 DeVille with 80k miles has been driving absolutely fine, smooth and powerful, when tonight I am cruising slowly around my neighborhood looking for parking and the car suddenly starts shaking. I hoped it was the road surface but soon convinced myself otherwise -- it shook when stopped, a little less in Neutral than in Drive. I park and then manage to pull the code P0300 - Random Misfire. Only one. Funny how a car seems strong and bulletproof one moment and then has a sudden stroke.

I know there is a lot written about this and various possible causes, but does this sudden onset suggest any particular mode of failure more than others? Car is going to mechanic tomorrow -- hopefully on its own power. I have a penchant for punching it, but when this started I was going maybe 10 or 15 mph, barely over idle.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Exercising the engine is good, so that had nothing to do with the near-stall. The P 0300 is a generic misfire code - a shop or parts store scan will usually insert the offending cylinder numbers into the P code - P 0302, P 0307, etc..

Could be anything from ignition problems to injector mechanical or electrical problems or even the fuel itself.
 

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Discussion Starter #3
Hmm... just hmm... Additional clue is that when I started it this morning it ran perfectly smoothly but after a twenty minute drive to the shop was starting to shake and on the way back was back to where I started. Sulfurous smell from exhaust, I take it that has something to do with unburnt fuel. Shop's answer was, use the car, let it go through several more cold hot cycles, see what codes develop. And do some research. He seemed to think my $25 scanner would pick up those P 0302, P 0305 codes also.

He is a small business owner and gives me a break on prices so I have no problem with this partnering approach to service. I always buy my super-premium fuel at the same BP station but that doesn't mean there are no quality variations - I've noted in the past that sometimes the car flies like it was 2500 lbs. on racing fuel and sometimes it's grumpy, but I know that could be many other things. I guess I either learn or say "Here.YOU figure it out" and pay a lot more money. Been there.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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Hmm... just hmm... Additional clue is that when I started it this morning it ran perfectly smoothly but after a twenty minute drive to the shop was starting to shake and on the way back was back to where I started. Sulfurous smell from exhaust, I take it that has something to do with unburnt fuel. Shop's answer was, use the car, let it go through several more cold hot cycles, see what codes develop. And do some research. He seemed to think my $25 scanner would pick up those P 0302, P 0305 codes also.

He is a small business owner and gives me a break on prices so I have no problem with this partnering approach to service. I always buy my super-premium fuel at the same BP station but that doesn't mean there are no quality variations - I've noted in the past that sometimes the car flies like it was 2500 lbs. on racing fuel and sometimes it's grumpy, but I know that could be many other things. I guess I either learn or say "Here.YOU figure it out" and pay a lot more money. Been there.
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hmmm - whee to start -
Shop's answer was, use the car, let it go through several more cold hot cycles, see what codes develop
TERRIBLE advice -
this guy sounds like a parts-changer - NOT a mechanic -
dumping raw fuel into the catalytic converter WILL destroy it fairly quickly -
adding a LOT of unnecessary expense to the repair bill -

He seemed to think my $25 scanner would pick up those P 0302, P 0305 codes also.
VERY disappointing -
he didn't bother checking for codes? maybe he doesn't even have a scanner?

you could go to any big auto parts store to get codes read -
they'll do it for free -

once you discover WHICH cylinder(s) is(are) misfiring -
diagnosis is MUCH easier -

I always buy my super-premium fuel at the same BP station
you are wasting a LOT of money -
our cars are DESIGNED to run on 87 regular gas -
there is absolutely NO BENEFIT - none - zip - zero - zilch - to burning anything higher -
EXCEPT if you are towing a heavy trailer -
 

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2003 Deville
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Discussion Starter #6
... dumping raw fuel into the catalytic converter WILL destroy it fairly quickly -
adding a LOT of unnecessary expense to the repair bill -
I had wondered about that.

VERY disappointing -
he didn't bother checking for codes? maybe he doesn't even have a scanner?

you could go to any big auto parts store to get codes read -
they'll do it for free -

once you discover WHICH cylinder(s) is(are) misfiring -
diagnosis is MUCH easier -
I've included a photo of my device. Does it seem likely it might not even see these other codes? Odd that it could read P 0300 but not P 0308... I expect they are in the same format on the same data bus. On the other hand I have seen a YouTube of a device displaying misfire counts growing in real time on all 8 cylinders, does not seem my device can do that. Given such a device it would seem to be a good idea to hook it up straight away.

I always buy my super-premium fuel at the same BP station
you are wasting a LOT of money -
our cars are DESIGNED to run on 87 regular gas -
there is absolutely NO BENEFIT - none - zip - zero - zilch - to burning anything higher -
EXCEPT if you are towing a heavy trailer -
I believe the recommendation is somewhere in the owners manual. It would be plausible as marketing (If you have to buy more expensive fuel for you vehicle then it must be a special car, right!?), but I had convinced myself after I bought the car that it ran better on higher grade fuel. This could have been self-anecdotal evidence (see marketing psychology). A friend owns a '97 and its OEM recommendations goes all the way to you MUST run it on premium fuel.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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I had wondered about that.



I've included a photo of my device. Does it seem likely it might not even see these other codes? Odd that it could read P 0300 but not P 0308... I expect they are in the same format on the same data bus. On the other hand I have seen a YouTube of a device displaying misfire counts growing in real time on all 8 cylinders, does not seem my device can do that. Given such a device it would seem to be a good idea to hook it up straight away.



I believe the recommendation is somewhere in the owners manual. It would be plausible as marketing (If you have to buy more expensive fuel for you vehicle then it must be a special car, right!?), but I had convinced myself after I bought the car that it ran better on higher grade fuel. This could have been self-anecdotal evidence (see marketing psychology). A friend owns a '97 and its OEM recommendations goes all the way to you MUST run it on premium fuel.
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Does it seem likely it might not even see these other codes?
our built-in scanner can not display the individual cylinder(s) misfiring -
it is possible your hand held doesn't either -
which is why I suggested taking the car to an auto parts store -

I believe the recommendation is somewhere in the owners manual.
fuel and octane rating starts on page 5-5 in the Owners Manual -
THIS - copied directly from that page -
Gasoline Octane
Use regular unleaded gasoline with a posted octane of 87 or higher.
However, for best performance and for trailer towing,
you may wish to use middle grade
or premium unleaded gasoline

I had convinced myself after I bought the car that it ran better on higher grade fuel.

ya - WE call that the BUTT DYNO EFFECT -

A friend owns a '97 and its OEM recommendations goes all the way to you MUST run it on premium fuel.
CORRECT -
this is a completely different engine with completely different electronics -
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Yep ^ ^ ^

Our 2000 - 2005 Northstars are calibrated to run at rated power and torque on 87 octane fuels and running higher octanes will not (can not) cause the PCM to make any ignition timing changes to take advantage of the premium fuels. The same power ratings of 1999 and earlier were done for the 2000 and later engines with extensive combustion chamber, timing, compression ratio, and valvetrain redesigns.

As per the 2000 - 2005 owner's manuals - if you engage in trailer towing, extensive mountain driving, or full-out competition - you may want to run a higher octane fuel.

In any event, run a TopTier gasoline.

Fuel work is tricky - actual octane depends on what is/was in the tank before and what you put in now. 1/2 tank of 87 plus 1/2 tank of 93 = a tank of 90.

I run 87 Valero, BP, and Sunoco fuels in the 2002 STS and can testify that the car will go past 143 mph easily. (It's a Z-car)
 

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Discussion Starter #9
Yep ^ ^ ^

Our 2000 - 2005 Northstars are calibrated to run at rated power and torque on 87 octane fuels and running higher octanes will not (can not) cause the PCM to make any ignition timing changes to take advantage of the premium fuels.
Now that is more compelling than "Just use 87 octane, ok?". I appreciate a comment which goes one step further. I would be less than honest if I did not harbor a reason for giving the car 93 which, dragged to the sunlight, would look something like "because it deserves it!" as if it were premium cat food. Perhaps I can find some objective way to calibrate my rear end dynometer with reality.

The same power ratings of 1999 and earlier were done for the 2000 and later engines with extensive combustion chamber, timing, compression ratio, and valvetrain redesigns.
Autos are interesting machines.

As per the 2000 - 2005 owner's manuals - if you engage in trailer towing, extensive mountain driving, or full-out competition - you may want to run a higher octane fuel. ... In any event, run a TopTier gasoline.
You don't have to tell me that last bit. The year, late 1980's, the car '84 Dodge, the gas station ... I don't remember the name except that it was on some traffic island kind of block in the Bronx that you would only pass making your way from one of the Harlem River bridges to I-95 by muscle memory. To go back to Portsmouth Naval Shipyard, btw... not understanding why I would have hit 1/4 tank before the end of the trip if I filled it up, but I did and the car began sputtering and failing and I got off and made it to another gas station on a wing and a prayer and topped it off. It ran again, turns out I could not go below 1/4 tank until I got the fuel tank drained and cleaned.

But if higher octane fuel is of some benefit under some conditions, then there must be something in the combustion environment which makes it so under stated driving conditions?

Fuel work is tricky - actual octane depends on what is/was in the tank before and what you put in now. 1/2 tank of 87 plus 1/2 tank of 93 = a tank of 90.

I run 87 Valero, BP, and Sunoco fuels in the 2002 STS and can testify that the car will go past 143 mph easily. (It's a Z-car)
Z-car? Is that part of the VIN? You intrigue me now; on paper I think the STS vs. the base was 300HP vs 275? My car will easily pass 100 on the way up, but I chicken out at that point on local roads -- it's not worth losing my license to test.

I enjoyed all the info in your post but my motivation in returning to this thread was to add a conclusion: so many of these maintenance tales seem to lack one .... it could be this, it could be that ... the rest is silence. So my friendly mechanic tried pulling the fuel injector wires off one by one and it seemed none of the ones in the front bank made the motor run any rougher -- so it was missing on four cylinders, more or less. He replaced the cassette and four spark plugs (yes, I believe they were the correct ones) and car again runs like a champ.

[/QUOTE]
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Car operating settings are set to the entire VIN.

The STS/DTS, as floorplanned, was a VIN 9 - 300 hp 3.71 final drive car - speed limited to the H-rated tire speed rating on the driver's door sticker.
The SLS/base/DHS was speed limited to 112 with a 275 hp 3.11 final drive and came with a S- rated tire.

Look on the driver's door sticker.

IF an STS was special-ordered out of the dealer's "black book" you could specify V-rated tires that raised the PCM speed limiter to "above 149 mph" or into the Z speed range for the tires. The fastest I have been able to run my car to was 143 mph GPS/speedo a few years back. I have access to an abandoned airport runway with a half-mile paved farm road at one end. Cooper CS5-V Ultra tires.

speed_chart.gif
 

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2003 Deville
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Discussion Starter #11
Ah. Z for tire rating! I had bought a set of Cooper Evolution All-Season 98T Tires, which turn out to be speed appropriate for the base model - so at 100 there is not too much further to go. I also have a disused airstrip near me and it has been rumored that it is a good place to take your car for a quick test early some morning, but the whole place has been shut down for the pandemic (part of a recreation area). On the other hand I am aware of the Achilles heel involving the head bolts and possibly this contraindicates pointless measurements of top speeds and accelerations. I have a '94 Corvette to use appropriately inappropriately.
 
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