Spark plugs sooty and black

WOODY1000

MEMBER
CHEVROLET

I bought a 1991 chevy beretta GTZ with 87,000 miles, it has 3.1 engine, it boggs down when you went up a hill and black smokes little out the exhaust when you step on the gas. I changed plugs and a couple were black and sooty, (carbon build?), A friend told me they werent firing right, but I am getting fire through my plug and wire. Am I using a hot enough plug or is it a blown head gasket allowing water leak in the motor or? I dont seem to have a problem with it running hot. Thanks Jess

2 Replies

MIKEYBDMAN

MECHANIC
623 POSTS

A couple of things can ease your mind. First off, you can do a compression check on all of the cyliners and see if they are all about the same. If the two that have a build up on the plugs are lower than the other 4, you may have a major engine problem. If they all test ok, then I would turn my attention to fuel delivery. It sounds like you are running rich, atleast on those two cylinders. A bad fuel injector could be a couse, or a bad fuel regulator. The engine computer controls the flow of fuel to mix with the air for proper burn. If one of the sensors giving the computer has gone bad, it can give false reading to the computer causing it to make more fuel than it needed.
I would say though, since only two plugs show signs of running rich, it may be a problem with the injectors at those cylinders.
Good luck