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'04 Deville misfire


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The '04 Deville developed a severe misfire the other day.  Blinking service engine light and PCM B0300 CURRENT misfire code was stored.  I suspected it was a bad coil but all eight coils were replaced about three years ago as they failed one by one back then.

I removed the coil assemblies and spark plugs - one bank at a time and tested for spark - all eight coils had spark.  I noticed a fair amount of oil in the #3 or #5 plug well and cleaned it up and reassembled everything.

I started the car and the PCM P0300 changed to history but I could still feel a misfire.  I don't have a Tech 2 so I am not sure what cylinder is misfiring or why it is misfiring when there is spark on all cylinders.  I suppose it could be a bad fuel injector - I plan to check into that in a couple of days when I get some time.  I am also studying the information on the PCM P0300 code in the service manual.  

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Is it the 2 coil pack units? One for each bank.

A decent reader will help alot to narrow it down to the cylinder(s) at fault.

My very honest opinion is Do not waste any time researching that code. Will be no help. You need the cylinder  code.

That code is so generic that useless info will come up forever

Is there any chance it could be a fuel quality issue? If so it may pass

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I don't think it is a fuel quality issue - I don't think it was fueled up prior to the misfiring (wife's car).  It is not re-setting the PCM P0300 code but I can definitely feel it misfiring.

None of the parts stores in my area have the ability to read the misfire data - only the codes which I did from the dash.  What brand of scan tool do you use as a Tech 2 is out of my price range.

I am going to check the PCV elbow at the intake manifold and the injectors to rule them out.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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1 hour ago, rockfangd said:

Is it the 2 coil pack units? One for each bank.

 

It is a coil on plug system - eight coils.  I have verified I have spark on all cylinders.  The spark plugs and coils are OK.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Ok. I have a OTC one that is cheap and reliable. Honestly have had it for a long time so I am sure it has been replaced.

Sadly verifying spark is not always good enough on todays systems. They are so sensitive that a spark may still not be good enough.

A repeat failure on a coil would not surprise me. I have changed alot of them.

If you can get the specific cylinder code you can swap the coil in question and see if it follows.

If problem stays to the same cylinder then you likely have another issue, Fuel, cylinder, etc...

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I discovered a very loose boot that connects the PCV valve line to the intake manifold and thought I had it diagnosed.  I put a zip tie at each end of the elbow and it is now snug.  Took a test drive and PCM P0300 set, blinking service engine soon light.

The intake coupler was replaced when I had the head gaskets done three years ago so I doubt that is the issue.  When those tear, they set the PCM P0171/P0174 code and those are not set.

I need to find someone with a scan tool that can monitor misfire counts in order to proceed with the diagnosis.  I believe it is something simple but I don't want to fire the parts cannon at it.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Can start with just a code reader, something that can give you the codes. Most will give you the actual cylinder misfire code. It will give you the P030X(s) and help to lead you in the right direction

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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  • 4 weeks later...

I figured out what the problem was - a bad coil on the rear bank.  When the engine was cold, the car ran fine.  Once the engine was up to operating temperature, the misfire would occur.  Sometimes, the misfire was slight and other times, it was severe.

I borrowed a friend's Actron CP 9180 scan tool but it did not have the capability to display misfire counts and all it did was display PCM P0300 which was no help... I went to the storage facility where I keep my '05 Deville for the winter and removed the front set of coils.  I installed them on the front bank of the '04 and took it for a drive - it was misfiring once the engine warmed up so the front coil unit was good.  I then removed the rear coils and installed the front coil unit from the '04 in the rear bank and put the '05 coil unit in the front bank.  I took the car for a drive and it ran fine.  When the warranty replacement arrives, it will be an easy swap on the front bank vs. fighting with that air pump solenoid unit on the rear bank.

 

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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