Carbon fouling on only 1 spark plug
#1
Instructor
Thread Starter
Carbon fouling on only 1 spark plug
Is there any reason why the driver side rear spark plug nearest the firewall would have repeat carbon fouling, when all the other plugs are fine?
This is on my 72 base motor. 58K miles. Never rebuilt, but it had a 327/350 clone cam installed before I bought it. It definitely needs valve seals, lots of smoke upon startup and some smoke while running. Uses about a quart of oil per 800 miles.
This plug fouls with big chunks of carbon about every 1000 miles to the point of not firing anymore. Other plugs are fine.
This is on my 72 base motor. 58K miles. Never rebuilt, but it had a 327/350 clone cam installed before I bought it. It definitely needs valve seals, lots of smoke upon startup and some smoke while running. Uses about a quart of oil per 800 miles.
This plug fouls with big chunks of carbon about every 1000 miles to the point of not firing anymore. Other plugs are fine.
#2
Melting Slicks
I'll take a shot at your problem. Either broken ring on that cylinder or intake manifold seal leak. Time to do a leak down check and see how this cylinder compares to the others.
#6
Team Owner
Auto trans vacuum line?
If you have an automatic transmission, and the vacuum modulator is plumbed to that particular cylinder's intake runner, the modulator might be ruptured and drawing fluid into that particular chamber.
Sounds improbable but I've had it happen...twice. If you think this might be the problem, check if there is fluid in the vac line. The cure is to replace the modulator.
Sounds improbable but I've had it happen...twice. If you think this might be the problem, check if there is fluid in the vac line. The cure is to replace the modulator.
#7
If you have an automatic transmission, and the vacuum modulator is plumbed to that particular cylinder's intake runner, the modulator might be ruptured and drawing fluid into that particular chamber.
Sounds improbable but I've had it happen...twice. If you think this might be the problem, check if there is fluid in the vac line. The cure is to replace the modulator.
Sounds improbable but I've had it happen...twice. If you think this might be the problem, check if there is fluid in the vac line. The cure is to replace the modulator.
#8
Burning Brakes
Member Since: Aug 2005
Location: Hudson Falls, N.Y. 76 Vette Modified L-48
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I have the same problem, except it's both rear plugs, 7 and 8....was thinking of hotter plugs in those two cylinders?
I'll be watching for more input....
I'll be watching for more input....
#9
Instructor
Thread Starter
FYI the car is a 4 speed, so it is not the automatic specific problem mentioned.
I left out the fact that the guy that put the cam in changed a few things on the car. There were lots of loose nuts and bolts in the areas where he worked on something, including the intake manifold. I bet that the intake manifold is leaking...
Also the car does need valve seals pretty badly, so it could be the low spot in the engine thing also.
I was hoping someone would say it could be something with the intake. I have lots of other projects to complete on the car before tearing into the bottom end (rings).
I left out the fact that the guy that put the cam in changed a few things on the car. There were lots of loose nuts and bolts in the areas where he worked on something, including the intake manifold. I bet that the intake manifold is leaking...
Also the car does need valve seals pretty badly, so it could be the low spot in the engine thing also.
I was hoping someone would say it could be something with the intake. I have lots of other projects to complete on the car before tearing into the bottom end (rings).
#10
FYI the car is a 4 speed, so it is not the automatic specific problem mentioned.
I left out the fact that the guy that put the cam in changed a few things on the car. There were lots of loose nuts and bolts in the areas where he worked on something, including the intake manifold. I bet that the intake manifold is leaking...
Also the car does need valve seals pretty badly, so it could be the low spot in the engine thing also.
I was hoping someone would say it could be something with the intake. I have lots of other projects to complete on the car before tearing into the bottom end (rings).
I left out the fact that the guy that put the cam in changed a few things on the car. There were lots of loose nuts and bolts in the areas where he worked on something, including the intake manifold. I bet that the intake manifold is leaking...
Also the car does need valve seals pretty badly, so it could be the low spot in the engine thing also.
I was hoping someone would say it could be something with the intake. I have lots of other projects to complete on the car before tearing into the bottom end (rings).
I would expect wet oil soaked plug with the intake runner not sealing. Common problem.
#11
Pro
Member Since: Oct 2004
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You can take this for what its worth. I had a boat engine 427 with an old edelbrock intake, P/n c-- something, one plug would foul in about 10 hours of operation. After changing everthing I found out that model intake was prone to cracking between the cylinders. I changed manifold and problem solved. Dave
#12
Melting Slicks
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The intake gasket start to leak at the rear, fouling out the rear most plugs while the otheres are fine. Replaced the intake gaskets on my '79 Chevy truck and took care of the problem.
#16
Instructor
Thread Starter
I'm pretty sure it is the intake, as I discovered several loose bolts when I first bought the car and was diagnosing carb problems (which turned out to be clogged ilde air circuit). I probably won't be tearing this apart too soon, as I am more interested in a few other projects on the car first.
One more question on the subject though. The plug is fouled with big chunks of carbon, not oil fouled. The first time it happened (driving from NJ to FL) the entire electrode became encrusted. Chipped the stuff off with a sharp screw driver, and all was well again for a while. I have changed the plugs since then with continued problem. All of the plugs show signs of burning a bit of oil (valve seals). Could an oil leak be causing these big chunks of carbon? Not sure what creates the carbon, is this oil leaking into the hot floor of the intake manifold, than breaking off into the cylinder?
One more question on the subject though. The plug is fouled with big chunks of carbon, not oil fouled. The first time it happened (driving from NJ to FL) the entire electrode became encrusted. Chipped the stuff off with a sharp screw driver, and all was well again for a while. I have changed the plugs since then with continued problem. All of the plugs show signs of burning a bit of oil (valve seals). Could an oil leak be causing these big chunks of carbon? Not sure what creates the carbon, is this oil leaking into the hot floor of the intake manifold, than breaking off into the cylinder?