Intro/Trouble shooting help thread.

[Jakemd98]

Hey all.... sorry i haven't been on in a while. School and work got the best of me. I finally replaced the injector a month or two ago, and less than 20 miles later my fuel pump went. So needless to say the Yukon has been a nice lawn ornament recently. I replaced the fuel pump last week and it seemed to run pretty good, but now after about 40 miles i am getting a cyl 4 misfire when it is warmed up. And still getting oil in the cyl. Is there a easy fix to this or am i looking at having to do new rings?

Thanks for all your help!

 

[SunlitComet]

a leak down test would be recommend to see if it is leaking past the piston ring. or do an in-vehicle service check of that cylinders valves for looseness in the valve guides to valves or even change the valve stem seals on them. If it only happens when warm I don't think it will be rings. I think when warm the oil thins and gets past you valves into the cylinder but you rings should tighten a little. With pressure down in that cylinder and it only misfiring when warm I would suggest that or a minor gasket crack somewhere.

 

[Jakemd98]

Gaskets seem to be fine... we pressurized the cooling system and it held pressure with no leaks.

we pulled the valve cover not too long ago and checked springs and they looked good so i just dismissed the valves being the issue. Guess it's time for a leak down test and see where it is going. I appreciate the help and ideas.

 

[SunlitComet]

Actually I was thinking a head gasket crack between an oil line and cylinder but yeah try a leak down to see if it is leaking past the ring. Also if you have not already maybe replace the plug it it got fouled really bad while still firing. it may have done some unseen damage to the plug. $6 would certainly be worth it if the plug was messed up real bad.

---------- Post added at 12:33 PM ---------- Previous post was at 12:31 PM ----------

also wiggle the valves when doing the leak down test.

 

[Jakemd98]

i have replaced that plug every 50 miles or so... it gets better then progresses back. Ill may do the leak down test friday and see what happens.