one plug fouling?

GT6Steve

GT6Steve

Well-known member
Joined
Jul 13, 2008
Messages
751
Location
Las Vegas Nevada
Greetings Gurus,

I've got a street driven 1981 with a rebuild about five years ago. over the last ten years it's been driven on city streets with stoplights and seldom elevating the RPM's. Just city driving. Never a problem, the thing ran great!

Nine months ago I took a new job out of town so now it gets 30 miles of highway each way, typically holding at 2500-3000 RPM. Now I have a problem with the no 8 spark plug fouling on me. It will build up a massive deposit of a tan white color until the plug finally fails. I went one grade hotter in that hole but that just extends the problem.

I'm thinking fuel with the white but don't know...Any thoughts?

Thanx, Steve in Las Vegas:hi:
 
Last edited:
big2bird said:
big_G said:
Valve guide seal. Typical on sbc's. Maybe replace just the seals on #8.
Click to expand...

I dunno G. #8 DOES typically foul on SBC, but he is talking tan/white fouling.:bonkers:
Click to expand...

That's exactly the kind of info I was after, whether there's an intrinsic issue. So why does number 8 foul? Right rear, in case I'm not using the correct numbering.

My thinking was a manifold distribution problem but I've read that the 81's had a very good manifold and the aftermarket units are only slightly better. Q-Jet BTW.

Thanx for sharing your knowledge, I'm just learning Chevies...:oh:
 
#8 plug runs leaner and hotter due to it's distance from the carb. Excess oil deposits will turn white and caked up. Running too rich usually just stays black and sooty.
 
MY experiences with #8 cyl mean you have a slight head gasket leak to water jacket.....don't ask.....


:cussing: could put air into the water jacket, pumped to rad cap relief, I do that with some a/c gauges and compressor fittings, I do all sorts of crazy crap like that, so to pressurize the water jacket, and take the spark plug out, stick a stethescope tube down in there and listen....

:hunter:
 
#8 plug runs leaner and hotter due to it's distance from the carb. Excess oil deposits will turn white and caked up. Running too rich usually just stays black and sooty.

"These are light-brownish deposits that are encrusted to the ground and/or center electrode(s). This situation is caused by oil and/or fuel additives. This condition can cause misfires.

The cure for this is to verify worn valve guides or valve seals, not using fuel additives, or you might even try changing fuel brands. By the way, a hotter plug is what most people try to fix this problem. You need to first understand that the plug is NOT typically the problem."

sparkplug.jpg
 
Thanx fort that,
I knew a hotter plug wasn't a solution, just a band-aid.

I'll do a couple of tests with the exhaust gas thing and the rad pressure tester. I was just wiondering if there was an intrinsic weakness there. This is my first V8 after a half century of British iron. A bit of a learning curve:)
 
There you go. I've seen the modulator(s) go bad on 350/400 trannys and since the vacuum is taken from the intake @ the runner for 8, guess which plug gets it?
 
Interesting. So what wiould the trans be doing if the modulator was leaking? It IS sluggish coming in from a stop when cold.
 
Shifts could be lazy. It might act normally too. Depends on how bad the diaphragm is. A small leak it could work just fine but seep fluid thru it. There's a 1/4" steel line that runs right next to the trans dipstick and hooks over to the vacuum port on the right side of the intake with a short rubber hose. Pull that off and see if it's oily inside.
 
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