Misfire saga

[Bobbyd3633]

I have a 2003 4.0 SOHC XLT 2WD that's misfiring on cylinder 1 at low RPM. I had the engine out and replaced all the timing chains and tensioners. Reinstalled engine, started it up, ran fine until it warmed up. When idle dropped it started missing. Put an engine analyzer on it and pinpointed it to the #1 cylinder. It only misfires at idle, at RPM over 2000, no misfire. I've changed plugs, wires, coil, injector pigtail, and injector. No change. Has good compression and leak down. I hear a faint rocker noise, so I removed the intake and valve cover suspecting valve spring or rocker trouble. Everything looks fine, but ordered new valve springs just in case. Turned motor over with the starter and all looks normal. I'm stuck, it has good compression, so I'd say the valves are seating normally. Leak down was good, so I'd say the rings are fine. The only thing I can think of is a valve spring problem, but they are not broken, maybe lost rate?

 

[Bobbyd3633]

Oh yeah, forgot to mention that I checked injector wire with noid light. When you pull the wire from the injector at idle, no change. No codes present or CEL. Also checked for vacuum leaks, none present.

 

[Bobbyd3633]

Fixed!!

Update:
Found that the compression gauge I used was faulty. Only had 70lbs on cylinder #1 . Removed head and found bent exhaust valve. Local machine shop checked and guide and seat were fine. New valve, valve seals and decking the head only $115! Will have back tomorrow and installed tomorrow evening.

 

[Bobbyd3633]

Update

Head back on and all is well. Runs great, no miss. Bought for son's first car, he is very excited!

 

[apenland01]

Glad you found the problem and got it fixed for not a lot of cash!

 

[Bobbyd3633]

Thanks! I haven't worked on a street car in 20 years, just race cars for a living. Bought this as a first car for my son for $550. I have about $2100 in it now and he has a good car.