Misfire Cylinder 2 Troubleshooting

[cdurth]

Hello all.


I am troubleshooting my '00 4.0. It is currently throwing a cylinder 2 misfire, running rough.


Engine has 198k, non TUPY head, from what i can tell, it hasn't cracked yet.The PO def abused it a bit, the cooling system was trashed, blown head gasket, and piston #6 skirt broke off shortly after i got it running without over heating. I ended up just popping a new piston and rings into #6 after a hone. I also checked all the cylinder walls and didnt notice anything popping out (also, i dont really know what i'd be looking for, but nothing was scratched or super worn)


I did dry compression tests w/ warm motor with the following results:
1-100
2-62
3-120
4-137
5-120
6-133


I have a HF leak down tester that I tried to use. It would appear that I could only hear air leaking from the throttle body. No pressure from valve cover or dipstick, no bubbling coolant, nothing from tailpipe.
I found TDC using a small rod. I wasn't positive on the stroke, so i cycled the engine 4 times and completed the test, also definitely could tell when the intake valve would open more. I am going to do this test again tomorrow to compare the sound on cylinder 4 and 6.


Just looking for tips before I pull off the head again and begin to learn about valves.

 

[Unclewolverine]

Um, I its early so I may be missing something but the answer is obvious. Definitely something wrong with #2 intake valve sealing. If it sat a long time it could of developed rust on the valve seat, or the valve could be bent. The only other test you could do with the head on is take out the push rod and check for leak down in case the lifter is stuck at full extention but ive never heard of that happening.

 

[RCP Phx]

Before you tear anything apart and it's still running, load it up with Seafoam and lets it rest for a while. Then restart it and go to the next step.

 

[Unclewolverine]

That's a good idea, could be some carbon on the valve.

 

[cdurth]

Hey all, thanks for the suggestions. I've tried most of them already.


I ended up finding a TUPY head from the JY, bit abused but was able to clean and seat the valves on cylinder 6 which had the piston head fail and punt around. luckily, i dont see any obvious damage, and was able to lap the valves to seal.


I think i am going to call around local machine shops and see what it would cost to get surfaced and ground.

 

[cdurth]

UPDATE


JY Tupy was solid. Ended up doing valves, seats & seals.
Pulled old head, leak down test was correct, intake valve on cylinder 2 was not seating.