Im sure youre all sick of seeing the same threads from me but Ill put this as simple as I can. I have a random misfire from one cylinder. I have changed:

-Plugs
-Wires
-Cap
-Rotor
-Injectors
-All 8 injector connectors


First crank up of the day, smooth as glass, for about a minute, then starts loping. While accelerating or cruising I can hear the engine gain and lose power from one cylinder. Sometimes it runs so smooth the tach doesnt move at idle. Rock solid. Then a few minutes later it will start missing while cruising or idling...the whole exhaust system will shudder and the tach wiggles in tune with the miss. Then it will snap out of it and run smooth again for a few minutes.

I found cyl 3 and 5 had oil fouled plugs as shown here.




The rest looked normal. Changed the 2 bad plugs with good ones, and it doesnt fix the problem. Still random misfires. Sometimes smooth, sometimes rough.

I want a good used LB9 to swap in.

Any help would be great.

 

It might be a problem with the fuel injection pulses to those 2 cylinders. That should be easy to see with a scope since they should all be the same width otherwise it would be an ignition problem. You could try indexing the plugs to see if the spark might be blown out ocassionally.

 

I am convinced its not fuel. They are Bosch III with all new connectors, which I noid checked and were good. I had this problem before I changed the injectors.

How do I index the plugs and check for blowout? You mean gap them?

Thanks for the help so far.

 

To index first mark the white porcelain inline with the open end of the gap reinstall and see if the gap is pointing towards the intake valve if so use copper indexing washes to point it away, or just put plugs that can be gasped to .035 to minimize the distance the spark has to jump.

 

I see. I will try that. Since I am convinced it has something to do with these two plugs that keep fouling.

But I am wondering why they foul like that so bad? Those plugs had around 2000 miles on them when I pulled them. And these were the same two plugs that were fouled when I bought the car. Bad rings or valve seals?

 

You always want to do easiest & less expensive things first. So do a cylinder leak down test if they are leaking add a squirt of oil to determine if it's the rings or valves