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So, I am having trouble with my 89 mustang. It was running real strange at cold start. I decided to change the plugs, and found that one cylinder was really really black. After I changed them, I noticed it ran a little better, but still bad at cold start up (black smoke out of exhaust until warm). After a few days, I pulled the spark plug out of the cylinder that was black. It was sooty again. I changed the wires, cap and rotor, cleaned the fouled plug, and still it sucked. While running, I pulled the wire from the plug, and there was no change.,..... I'm running on 7 cylinders... Without changing valve seals, what else would be a cheap try to fix my problem?
 

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Check 3 things (1) pull the plug out and check to see that it fires (do this by inserting plug into plug wire and looking at the gap and see if there is a visible arc when the motor is running. (2) Is the cylinder getting gas. If the cylinder is not getting gas then it doesn't matter if you have spark, because without gas it will still be a dead cylinder. Motor needs Air, FUEL, and SPARK. Now which one of these is missing?
 

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If it's getting real sooty it sounds like it's getting fuel and at least combusting sometimes. You might have a fouled injector that's stuck or intermittently working? I've heard of them sticking open causing a constant slow leak into the cylinder causing all sorts of fun similar problems. Maybe try and swap that injector with another cylinder and then pull the plug from one of the cylinders you swapped and see if there is a difference then? At least count out the injector itself. Process of elimination. Sounds like you've already crossed off a bunch. Ask ourselves, what's left? Oh, and check your big wire harness connectors behind the intake.
 

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I had a fuel injector wire chewed up by a rat, causing only 7 cylinders to hit.
yea, it's amazing how these little varments like to chew things up. glad you found the problem.
 
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