CAR STILL HAS CYLINDER MISS-FIRE(or so it seems) HELP!!!

Question

I have a 1994 caprice with a 265ci. 4.3 v8, engine is almost identical to the Lt-1 in the 94-96 caprices & impala ss'. As of recent I had noticed an engine miss. I figured since the car has about 140,000 miles it was due for wires (I had done the plugs before). So I replaced plugs and wires and upon removal of a plug from the #? cylinder I noticed a plug was badly fouled out. I thought AHA! heres the problem the wire must be bad. Well after plugs and wire no change. Then I proceeded to take on the daunting task of changing cap and rotor. This unit is located behind the crank balancer and water pump, a bear to get to. So I just finished that yesterday, actually replaced the entire opti-spark distributor. Now it has new plugs wires dist., and although the cap and rotor was in extremely bad shape on the old unit (before replacement) it still seems to have a miss after all this work. I checked the egr it was clogged and stuck, I cleaned all the carbon out and it moves fine now, and when I press it in with engine running it wants to stall engine so no clogs in intake. I AM AT A TOTAL LOSS. Can’t figure out what other sensor might do this. Maybe a vacuum leak? Anyway you only really feel the miss at idle or when the engine kicks into overdrive at low RPM's. Not really a sever miss, but very, very bothersome. HELP! please any advice or recommendations would be deeply appreciated. Thanks for reading.

Answer 1

it sounds like a weak spark plug never buy cheap ones change them for main dealer ones see if that helps if the plugs get fouled up again the motors running rich or could be the head gasket is worn you could try doing a compression test in each cylinder that way you would know if the head gasket is worn

Answer 2

You didn't say how the spark plug was fouled.  If the plug had sticky black **** then you have too rich a mixture in that cylinder. That would mean a leaky or dirty fuel injector. It could still be a result of a vacuum leak (especially when the misfire occurs at very low load conditions with high vacuum). The O2 sensor can pick up too much oxygen in a vacuum leak and fool the computer into a rich condition. Check for a vacuum leak and try some injection cleaner.

If it was carbon fouled (sooty black layer) then you have an ignition problem. There's unburnt mixture in the cylinder.  Maybe you gapped the plugs wrong and it is particularly bad in that one cylinder. One thing is for sure; if the gap is too small it can cause arcing in the rotor and cap and could have lead to the condition that you mentioned about the cap and rotor. Your sooty EGR valve might be a clue to this also. Is your EGR valve located next to that cylinder?

If it was oil fouled (you'd know that) then obviously you have a major problem with that cylinder sealing. Valve seals would be the culprit there (especially at low load conditions). Hook up a vacuum guage and see if you get a bouncing needle. If so, Bingo!

Reading plugs is a great way to diagnose trouble. But you have to read the right language. Replacing the spark plug does not cure the condition that caused the misfire so it can still exist.

Answer 3

if your car has any oxygen sensors, change them.  

Answer 4

You can safely run the vehicle on 4 cylinders.  Start with the one that plug that was fouled.  Pull that wire and see if you have the problem.  If the problem goes away you might have cylinder/head issues or maybe fuel flow problems to that cylinder.

May the force be with you.