PCM update - needed or just guessing?

I got hold of a compression tester and got the following results: cyl 1, 3, 5 & 6: 180-190psi. Cyl 2: 155psi. Cyl 4: 60 psi. My friend said to hold my hand by the exhaust pipe while it’s running and describe what I can feel both when it’s rough and when it’s smooth. When it’s rough, it has a puff-puff-puff quality to it, and feels like being slapped in the hand with a potato. When it’s smooth, it’s a lot less “puffy” and a lot less force overall. He said it may be a bad exhaust valve, based on that.

No one seems to be giving me a reasonable explanation as to why I can get it to run smooth, and why it goes from rough to smooth to rough again for the reasons I’ve stated in earlier posts.

I’ve got one local mechaninc telling me it’s rings, another saying it’s a valve, and yet another saying it can’t be rings or a valve. He insists it has to be the fuel injector because I can get it to run smooth. Another guy is telling me it may be gunk in the rings that’s getting unstuck when it warms up, and still another says it’s a valve that’s being temperamental.

At least you guys all pointed to compression first, and so I hope you can point me to what is within reach for a poor boy like me. I priced a tool to check rail pressure, and I can’t afford it for just one use.


I just re-read your 1st post… I think that it only feels smooth, becasue a miss will be more noticable in low RPM… You are still running on 5-cyls, and while it is pobably running low on power it will still “smooth” out some what. I had a friend who had a V8 and when we did a tune up on it one of the sparkplug wires had litterally fallen off the plug, who knows how long ago… He could not belive how much more smoother the car was after the full tune up.

TRY THIS… Take a dollar bill and put it next to the exsaust pipe while running. If it trys to suck the dollar into the pipe, you have a bad exsaust valve, if not is something else.

You next step should be to remove the valve covers and check the valve lash, especially on the bad cylinder.