Misfire Code P0306 Rides Again - 96 Eddie 160K 4.0l

[pclarke1]

Ok, so I have changed my plugs and leads, coil pack, fuel and air filters, removed cleaned and flow tested my injectors, cleaned my IAC, MAF & throttle body and replaced my upper manifold gaskets, and despite this my P0306 misfire code survives. All seemed well for a few miles, but then the CEL came back on. I also cleaned the connectors going into the coil. Any ideas?

The upside is that it is running better, until it gets warm and starts to mis (not constantly) at idle. The last couple of times the code comes on is during moderate acceleration. like on a freeway on ramp. The problem was intermittant starting 12 mths agao. Seemed to go away over winter (Fargo ND). The car starts smooth, but the CEL comes on once it has warmed up. I can clear it with my code reader, but it comes back after a few minutes.

My remaining theories are, bad compression or carbon. No sure of this because when I had the fuel rail off the #6 port looked the same as all of the others and as I recall the plug did not look too bad, or a bad ECM.

I can't get into my mechanic until this time next week any steps I should take in the meantime? I might throw a different brand of plugs at it just for grins on the weekend, currently I am running NGK V grooves.

 

[pclarke1]

And the winner is..... Low Compression 90 psi in cylinder #6. At this stage I see no reason to fix it, yes it will get worse overtime but I dont want to replace the motor or rebuild. Other cylinders were at 140ish. I am going to try "Engine Restorer", which while I realize is a little like filling the crankcase with chicken soup, but it probably couldn't hurt (much). I will post again in a few weeks with the result.