99 Tahoe - #3 Spark Plug Keeps Fouling

**Smartin** · 10-23-2009, 08:43 PM

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?

**unplugged** · 10-23-2009, 11:04 PM

Which picture does it look like?

See the full size chart here: http://www.aa1car.com/library/reading_spark_plugs.jpg

**Smartin** · 10-26-2009, 07:13 AM

Mostly like "ash deposits"

Someone else told me my intake gasket is probably leaking into that cylinder. Make sense?

**unplugged** · 10-26-2009, 07:53 AM

Originally Posted by Smartin

Mostly like "ash deposits"

Someone else told me my intake gasket is probably leaking into that cylinder. Make sense?

An intake leak into that cylinder would make it run lean, which in turn would make it HOT. Search forums for vacuum leak and test to see if you do have a vacuum leak. Looks more like an oil leak or additive deposits. Try running a couple of tankfulls of Chevron gas and see if the deposits clear up. Also, a combustion chamber cleaner like seafoam or Delco's brand would be a good idea.

**truheel1** · 10-29-2009, 08:48 AM

What did the old plug look like in #3 cyl??????? If it looked the same, its not something new from replacing the plugs. If it just started. Could be a dead plug from the start. I had a NEW dead plug in the golf cart would not fire. got another new plug works fine now...

**Smartin** · 12-10-2009, 09:19 PM

Ok guys, I finally had the symptom show up again. Pulled the plug and shots some photos....

What do you think? I am definitely losing coolant mysteriously....not sure about oil, though. Oil consumption seems consistent with the mileage of the engine.

**vncj96** · 12-11-2009, 12:49 AM

The best thing to do is a compression test of the cylinder. I had the same problem and I had to get the heads rebuilt. i had a velve taht wasnt closeing all the way.

**ahm1127** · 12-14-2009, 09:04 AM

I would use a combustion chamber cleaner like seafoam or AC Delco's brand cleaner first. Use an oil additive to clean engine, drain & run engine 1 quart low to see if there are any changes.
Good luck

**jnbascom** · 12-14-2009, 09:22 AM

Looks like you got a bad head gasket. The white deposits are from the engine coolant.

**Smartin** · 12-19-2009, 01:06 PM

I ran a compression test this morning to check for a head gasket failure. All cylinders checked out at around 180psi.

I found someone who will replace the intake gasket(s) for $250 plus the cost of the gasket kit. The dealer wanted $600 WITH my fleet discount.

He is picking it up this evening and delivering it back home tomorrow around noon. It'll be nice to have this finally fixed! Maybe I can get him to grease the slip yoke for me while he's at it....hmmmmm