02 tahoe misfire - ran out of ideas

[FreshLikeOprah]

Did you tune the after cat o2 sensors, out? If so, that could cause a issue. You can get a tune, OR, get 4 "spark plug non foulers" you will drill a 1/2 hole into two of them. Screw the ones not drilled into the o2 holes first. Then the ones drilled next. Then, screw your o2s in. Should help.

 

[livingez_123]

I would pull the valve cover off and check to see if maybe you have a bent push rod on that cylinder. it possible that a lifter can leak down at an idle and keep the intake from opening all the way. as the rpm go up so does the oil pressure and that could overcome a weak lifter at idle. you can't adjust the valves on the LS so I would start with the pushrods. Also try turning the engine over and watch the valves open on the cylinder in??? Make sure they look about the same as the other valves.

 

[hdrox88]

Did you tune the after cat o2 sensors, out? If so, that could cause a issue. You can get a tune, OR, get 4 "spark plug non foulers" you will drill a 1/2 hole into two of them. Screw the ones not drilled into the o2 holes first. Then the ones drilled next. Then, screw your o2s in. Should help.

The truck was purchased as is(no cats) so there is no telling on tuning come to think of it. I would be inclined to think that the miss would occur on more than one cylinder if it were related to not having cats. Maybe I am wrong?

I would pull the valve cover off and check to see if maybe you have a bent push rod on that cylinder. it possible that a lifter can leak down at an idle and keep the intake from opening all the way. as the rpm go up so does the oil pressure and that could overcome a weak lifter at idle. you can't adjust the valves on the LS so I would start with the pushrods. Also try turning the engine over and watch the valves open on the cylinder in??? Make sure they look about the same as the other valves.

The tech working on the truck said pushrods looked good and checked rocker movement while cranking and it appeared good as well. Not sure if he eyeballed it or put a dial indicator on it though. Not sure how much of a difference is needed to cause a miss.

 

[livingez_123]

I had an issue with a 5.7 in my boat. I had a miss at idle. Everything was brand new from the heads up. and it still missed. So I took it apart again and pulled the camshaft and checked the lobes and I had 1 bad lobe and it was the cylinder that was missing. After a new camshaft, lifters, chain and gears and properly adjusting the valves it purred like a kitten. My compression was fairly even across the board. I did have one cylinder that was more than 10% below the rest but it ran out real nice. I know the roller cams do have less tendency to go flat, but it's not unheard of. it might be a place to look also. if you have a good dial indicator and mag base you can check it without pulling it.

 

[hdrox88]

I suppose that is possible considering 240K miles and who knows what kind of maintenance. Unfortunately I don't have a dial indicator to check it myself.