Engine Misfire

[Duckie]

Can anyone can help with a engine misfire? 3100 V-6 Pontiac 125 PSI compression on all cylinders
Good spark, good compression, OBD says "Engine Misfire Cyl 4" Can hear a whisp in the exhaust like a leaking valve. Cylinder head has been removed and valves, valve guides, springs checked,all are good and valves shows no sign of leaking. Re-assemble cylinder head to block start engine and still can hear a whisp in the echaust, OBD still says misfire cylinder 4. Checked and replaced plugs and wires still misfires anyone have any suggestions?

[ramon357]

What are you using to check your misfires? You might try to switch coils. Is it just at idle or crusing or at WOT?

Ramon

[Flatrater]

Do you have spark at the plug? The wire off crank the engine do you have spark? Only 3 things cause a misfire fuel or spark or base engine problem, and if you have spark then it leaves fuel. since you ruled out base engine.

BTW I have done several engines and it is normal to hear leaking thru the valves. I have pumped up the cylinders with compressed air and could see the valves leaking air past the seats. I did this on a engine with no misfires.

[Duckie]

Thanks for the reply, forgot to mention a new injector has been installed. Clearing the OBD stays off and then after a few cranks the Service Engine Soon Light comes back on, check the codes...misfire cyl #4. My next exploration is to remove the upper and lower intake, examine cam lobes and followers there may be something there. Still open for ideas.
I have reverted back to the old days of trouble shooting by moving things around to see if the problem moves. Misfire on cylinder 4. I was taught in my younger days that if you hold a dollar bill to the tail pipe and if it were to be tried to suck it in the pipe, you had a bad valve or a misfiring cylinder. This happens to this engine and not my other vehicles. Still open for ideas.