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Spark Plug Fouled

f2502011

Jr. Member
Joined
Feb 19, 2011
Messages
342
Did a recent tune-up. All plugs looked good except the back one on the passenger side. It was caked with black gunk on the end and a little bit of brown on the tip. It doesn't smoke. I'm not sure how long the plugs were in there. In the short time I've had the new plug in, I've been keeping an eye on it, and it seems like it's starting to do the same thing. Would putting in a hotter plug (has Autolite 46s) help? If so is an Autolite 45 hotter or what is a hotter plug? Or maybe install a non-fouler on the plug? Or anything else to get by temporarily?

I plan to do a compression test too. What should the compression be for a stock 76 302? What's the best way to do the test? Is there anything else I should do to pinpoint the problem before I tear the engine down?
 

Explorer

Bronco Guru
Joined
Mar 2, 2008
Messages
4,390
Loc.
Raphine, Virginia
Make sure that cylinder is getting spark. Could be as simple as a bad or loose plug wire, or sign of serious problem. Compression test will help. A leakdown test will tell more. Compressiontest is as simple as screwing a gauge in the hole. Leakdown test, you apply air pressure to that cyl when it's at top dead center and see where the air comes out. Wouldn't tear it down till you know what you are looking for.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
Does anything feed diectly into the intake running feeding that cylinder? Brake booster, auto trans modulator, PCV, etc.? If one of those system is failing and sending it's fluid to the engine and into that runner it will foul that plug.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
I think 46s are hotter than 45's. You might have a valve seal or guide issue on that cylinder. Also figure that that cylinder is also where the oil drain back is if its draining slow due to gunk build up or pieces of old valve seals then you could be sucking oil through the valve guides.
 
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