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  1. #1

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    I Cured A Random Misfire Problem-3800 V6


    I think this should apply to any V6 GM makes...depending on select years.
    Dealing with a random misfire OBDII code of code P0300,and having bad misfires with the 3800 engine,I put new parts everywhere that did not solve the problem.

    Even out of preventive maint. I replaced stuff(kept old stuff too) that didnt seem to be TOO bad,just Old...was the coil module,coil packs and etc.Everything was old anyways so I justified myself for replacing everything I needed to do.

    On this particular 3800 engine,the back 3 plugs had metal plug boot heat shields with springs that slipped over the spark plug,plug boots.I always used them,because it was how the car came designed.I decided to remove them this time and the misfire stopped!

    Going back to the problem,I had checked the plugs and noticed some burn marks around the ceramic white area of the spark plug...didnt know for sure what it was,But assumed it was a misfire spark deposit when seeing it.Removing the metal shield tubes off the 3 rear plug boots gave me a new engine again.I dont know why or for sure it misfired with the metal shields,but somehow,on install they caused a misfire under load.

    See,before I found the problem, I had new plugs,new wires,new coils and module and the problem persisted.I used GM dielectric grease on the plug boots,and followed every step I always had for a good tune up.Had the injectors rebuilt,flow matched and tested by Rich at www.cruzinperformance.com

    They needed it,and the before and after rebuild specs was just WOW!

    I even changed the egr,new ecm,new intake man. gaskets(it needed it) and checked and tested everything with a snap on scanner.It still misfired badly under load.Still threw a code 300,random misfire,couldnt track for sure which one it was.Engine would rock back and forth when misfiring.Fuel pressure was in the normal area,didnt lose pressure or leak down,ever.

    Finally in the end,I found the problem was with the spark plug boot shields.
    I would have never guessed it,it happened by chance.Oh before I forget,and Before I threw new parts at the car,I had a GM dealer keep the car for the day and the techs had no idea what was wrong.They wanted to try the GM top engine cleaner treatment,like the seafoam treatment stuff,but I declined...I knew it was not carbon build up on the valves.I had ruled that out with the other work Ive done.

    What DID lead me to suspect the 3 back plugs was misfiring,was I used a timing light while the engine ran and the front plugs flashed the timing light just fine,as if in proper sequence,but the back plugs would skip and flicker at times.

    So now the engine runs like a champ and I wanted to pass this info along..sorry its long but needed to let you know I did all the obvious stuff and still had a problem figuring it out.I believe I posted about this a while back in another topic.I thought maybe the crank or cam sensor may be all thats left because the engine passed compression and valve train visual check ups for any broken parts.


    Mods,this 3800 V6 engine is inside my 95 olds mini-van but since GM uses this engine in so many cars,like the GP and others,I hope you leave this here in powertrain so it may help someone have time down the road.So many W cars uses the same engine from GM powertrian division that posting this in Other Cars felt wrong.
    I could have lied and said it was a 3800 GP or something but rather keep it all real.Im just glad to share my(long) story...hope it helps someone in the same boat someday.



  2. #2
    Mach 5's Avatar
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    Re: I Cured A Random Misfire Problem-3800 V6

    Good thing you figured it out. Ill keep that information in mind
    Founder of the Radical Revs Racing Team- Radical Revs Race Mods
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    Mach 5-1989 Pontiac Grand Prix SE- LG5 swap, GT3076r, Getrag 282, Birchmount
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    1985 AE86- 4age 20v, supra trans, 4.78:1 final
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  3. #3
    Forum Moderator digitaloutsider's Avatar
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    Re: I Cured A Random Misfire Problem-3800 V6

    Those heat shields are the biggest pieces of shit in the world. I've never re-used them.
    2006 Nissan Altima SE-R 3.5L 214ci VQ35DE DOHC 60 V6 | 6MT
    Raclingline HFPCs and Y-pipe, NWP VIAS delete, Goodridge SS brake lines, removed airbox snorkel, deburgered.

    1998 Jeep Grand Cherokee 5.9 Limited 5.9L 360ci Magnum Pushrod 90 V8 | 46RE | NV249
    Flowmaster 50 SUV muffler, 180 t-stat, CAI, does sick burnouts.

    1994 Ford Thunderbird SC Supercharged Intercooled 3.8L 231ci Pushrod 90 V6 | M5R2
    180 t-stat, intake, ASP UDPs, 10% S/C pulley.

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    Taco Decimator ShockTherapy's Avatar
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    Re: I Cured A Random Misfire Problem-3800 V6

    ditto.

    2005 Acura RSX Touring - DD/K20 frankenstein/coilovers/DCRH/Okada/Ktuner.
    2002 Toyota Tundra SR5 4.7 V8 - RWD/TRD twin screw/shitload of torque.
    2008 Toyota 4Runner Sport 4.0 V6 4WD - Winter beater/verge of death.
    2007 Nissan Versa 1.8S - Fiance's DD/autotragic/basic bolt-ons.
    Previous W's: 91 Regal GS, 94 GTP, 02 GTP. Don't quite know how I ended up with an RSX.

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    Re: I Cured A Random Misfire Problem-3800 V6

    Interesting. I'll definitely keep that trick in mind if I ever encounter any misfiring...

    Kevin B.
    2004 Chevy Impala 3400 V6 - Color: Victory Red

    1999 Chevy Tahoe 5.7 Vortec V8 - Color: You guessed it, Victory Red!

  7. #6
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    Re: I Cured A Random Misfire Problem-3800 V6

    that information is actually almost worth paying for lol thx
    rockfangd

  8. #7

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    Re: I Cured A Random Misfire Problem-3800 V6

    Im glad Im giving advice but damn I could have edited and made it alot smaller!


    I can get so long winded at times I dont realize it..just typing and the thoughts flow...but do hope It will eventually help someone in the future with similar problems to be able to narrow down whats wrong quicker.


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    Smile FIXED MINE TOO!!!

    Quote Originally Posted by 95oldsVan View Post
    Dealing with a random misfire OBDII code of code P0300,and having bad misfires with the 3800 engine,I put new parts everywhere that did not solve the problem.
    hope it helps someone in the same boat someday.
    THANK YOU!!!! my story is a carbon copy of yours! '95 firebird with 3800 motor. replaced spark plugs, replaced wires, replaced coil packs, replaced ICM, did spark jump test, cleaned fuel injectors, did compression test, change plugs again (autolite xp 606), regap, change wires again, wrap wires with looming, reroute wires, check for back pressure/clogged CAT. no matter what we did the car would just stumble all over the place, have no pep, flash MIL at me with P0300 over and over and over. VERY frustrating to say the least!
    as a last ditch effort, we took off the stupid F'in heat shields and like magic, the car runs like new again, NIGHT AND DAY difference immediately! WTF?? now I'm just confused as to why it ever worked with those things and I hope I don’t have melted wiresets and cracked boots to look forward to. but for now I've finally got my car back!
    thanks!

  10. #9
    Arrive Alive tornado_735's Avatar
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    A 6 year old thread about a U-Body misfire, on a W-Body forum, that just helped a person with an F-Body.

    This forum is awesome. Seriously.

    2006 Pontiac Grand Prix - 109k
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    1993 Range Rover County LWB 4.2L V8 - 151k
    "...then I saw that there was a way to Hell, even from the gates of Heaven..."

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  12. #10

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    FWIW, OP never mentions what kind of wires he used. I've always reused the heat shields and have never had problems with misfires since using ACDelco wires. When I first started driving, and had my old '91 Euro, I replaced the wires with some from Fleet Farm. They lasted about 3 months until they started causing problems. I later replaced them with "premium" parts store brand wires which lasted less than a year, and had one wire short out. I then replaced that lone wire with an old "good" one and all was well until I sold the car many years later. Every other vehicle I've owned, I went with Delco's and never had a problem reusing the heat shields. Just my $.02
    Just here for the pizza

  13. #11

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    GM isn't in the habit of spending money on anything that isn't actually needed.

    Remove the shields at your own risk. I see baked plug wires in your future.
    "The most negative fricken troll ever." --Bee Twenty

  14. #12
    Arrive Alive tornado_735's Avatar
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    Quote Originally Posted by Schurkey View Post
    GM isn't in the habit of spending money on anything that isn't actually needed.

    Remove the shields at your own risk. I see baked plug wires in your future.
    Has GM always been known to make the most intelligent decisions?

    Maybe that goes back to them not spending money on things that are, or are not needed...

    2006 Pontiac Grand Prix - 109k
    1995 Range Rover 4.0SE V8 - 121k
    1993 Range Rover County LWB 4.2L V8 - 151k
    "...then I saw that there was a way to Hell, even from the gates of Heaven..."

  15. #13
    If you fixed a random misfire by removing the heat shields, you have bad plug wires. They are arcing to the ground the heat shield provides. 40KV will arc easily

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