99 Tahoe - #3 Spark Plug Keeps Fouling

Discussion in 'The Choo-Choo shop' started by Smartin, Oct 23, 2009.

  1. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    I replaced the plugs, wires, dist cap, and rotor about a month ago. This past weekend, I noticed a heavy miss while under load. I asked the service manager at the dealer to check what codes it was throwing while driving. It was the #3 cylinder misfire. I pulled the spark plug and it had some heavy buildup on it. Like, stuff I had to use a screwdriver to chip off. I cleaned it up, and I don't feel the miss anymore, but I have to think that this is going to happen again.

    I replaced the coil this afternoon just for Sh!ts.

    What could be causing the #3 cylinder to continue to foul?
  2. TOPLESS71

    TOPLESS71 Sean O'Malley

    Are you losing coolant? Got a pic of the buildup on the plug? Antifreeze will turn into a hard white cement like substance on the plug. I've seen a lot of bad intake gaskets on those trucks(mine included).
  3. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    I had been losing some coolant, but I had an external leak somewhere....could never locate it. I don't appear to be losing it anymore (topped it off a couple weeks ago).

    The guy I bought it from said the intake gaskets were replaced, but I have no idea when it was done. I do smell antifreeze on occasion when I walk by the front end. I just never see any on the ground like I did when I bought it.

    I was under it this afternoon, and there was some antifreeze that has collected on the bottom of the engine, but I don't know where it was coming from.

    If the plug fouls like it did before, then I will get a photo of it.
  4. NJBuickRacer

    NJBuickRacer I'd rather be racing...

    Your intake gasket needs to be replaced. Went through the same thing on mine. You'll find that the intake port for #3 has slipped low enough to create a vacuum leak to the lifter valley area. An easy way to check is if you remove the oil cap while the engine is running, the rpm will change if the intake is the culprit.
  5. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    It finally started missing again....pulled the #3 plug and shot some photos...

    Still losing coolant....so I would assume it's safe to say I have an intake gasket leak.

    Attached Files:

  6. JOE RIV 1

    JOE RIV 1 Well-Known Member

    same thing with my 04 6.0 2500 hd:rant:
  7. Aaron65

    Aaron65 Well-Known Member

    I've found that the GM cooling system sealing pellets from the dealer work well...maybe worth a shot?
  8. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    I thought about that...might be worth a shot.
  9. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I thought about the same thing but I doubt if it will work. I was having pretty much the same problems with my `96 awhile back. I knew the gaskets should be replaced but I was having problems finding the time to do it. Then one day I pulled into a parking lot and got out of the truck only to find that anti-freeze was gushing out of the intake gasket on the right front corner. I had also been getting a misfire code from time to time. In addition, I started hearing a lifter noise on startups. Sometimes it would tick a couple times and go away, other times it would tick for a couple minutes. I picked up a set of lifters because I intended to change them as long as I had the intake off. When I pulled it apart I found that the intake gaskets were deteriorated so badly that no amount of stop leak would have done an ounce of good. I also noticed some anti-freeze in the lifter galley and it looked to me like it had been dripping from the intake gasket directly onto the #2 lifter. Lifter noise problem? I gambled and didn't change the lifters. I put the new gaskets in, changed the oil, and it has been quiet and leak free ever since. These are great engines with the exception of those intake gaskets. Do the engine a favor, fix it right and fix it soon before more damage occurs. Mine a 225,000 miles on it now with no other problems.

  10. JOE RIV 1

    JOE RIV 1 Well-Known Member

    bill,my chevy's has dexacool could i flush that junk out and put reg anti-freeze in?I don't think that should be a problem?thanks Joe Riv
  11. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I stuck with the Dexcool in mine and have never had a problem with it. I believe it is more friendly to the cars with more aluminum engine parts than the old stuff. I do drain it a replace it with fresh every two years but I'm a fanatic about that stuff. I also use Mobil 1 oil and Wix filters in the engine, change the transmission fluid and filter once a year regardless of mileage, transfer case, gear lubes and brake fluid every two years, etc............... IMO it's cheaper than having to replace expensive parts.

  12. 1drwgn

    1drwgn Poor Gearhead

    keep the dexcool, if you put reg anti freeze in it will react with the residue of the dexcool, and it will gum up,... prestone does have a universal coolant, works real well
  13. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    I paid a guy $340 to change the intake gaskets (that's including parts!). Much better than $600+ from the dealer, even with my fleet discount.

    The mechanic said the gaskets were absolutely trashed. I must've had a massive vacuum leak, because my brakes are no longer spongy, and it has twice the power it had before!! I'm going to keep an eye on the fluids to make sure I'm not still losing any through a head gasket or something. Although, I did do a compression test on it, and there was no indication of any leaks.
  14. Golden Oldie 65

    Golden Oldie 65 Well-Known Member


  15. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    THe dippy doo that replaced the gaskets forgot to plug in the cam position sensor. It was constantly throwing a code. I finally went to my buddy that runs a tire shop, and he hooked it up to his code reader. After he read it, he just laughed and popped the hood, plugged it back in, and away I went:laugh: That was a cheap fix.

    I still get a little bit of pinging under load. I threw in some seafoam when I filled up the tank this morning. Hopefully, that clears it up. I do have a new knock sensor I can install, if it doesn't stop.

    I tell ya...the to-do list on this thing never gets any smaller, it seems.
  16. 1 bad gs

    1 bad gs Well-Known Member

    dippy doo? the mechanic saves you 300 bucks and your calling him names? give the guy a break. have you ever made a mistake?:Do No:
  17. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    He drove it for 30 minutes with a "service engine soon" light on, and didn't bother to check WHY it was on.

    It wasn't on when I gave it to him.

    It took the guy at the tire store 5 minutes to figure out what it was.

    I'm thankful for the work the guy did, but he didn't finish the job.
  18. bobc455

    bobc455 Well-Known Member

    I have heard (and many people on the internet agree) that if you are not particular about flushing Dexcool out on a scheduled basis, that it will turn acidic. And the intake gaskets of that era are susceptible to being eaten up by the Dexcool.

    Everyone I know with a truck of that era has had to replace the intake gaskets.

    GM has apparently changed the material for the intake gaskets on newer vehicles, however they don't want to get involved with the intake gaskets on a recall basis and denies this is a problem.

    -Bob C.
  19. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    We've had to replace the intake gaskets on two of our company vehicles, and have heard many more stories of these beasties. Denying this as a problem has made them a lot of money. Obviously, it hasn't been enough:Dou:

    Oh well, the Tahoe runs great again! I just need to repair the headlight problem, get an alignment, tires, fix the air bag light, repair the leaking AC system, and replace the shocks.:rolleyes:
  20. bobc455

    bobc455 Well-Known Member

    Hmm. Can't blame those problems on the Dexcool...

    -Bob C.

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