Burnt valve possibly?

Cory · Post by **Cory** » 01 Jun 2010, 17:34

Hello everyone,
I have a previous topic on here about how my car misfires in the #1 cylinder at idle, and only at idle.
misfire ONLY at idle?

Well I ran a compression test just a few minutes ago and the #1 cylinder only registered 30 psi. From what I have read that is usually indicative of a burnt valve but I would just like to get you guys' opinion on anything else it could be. Someone suggested that it could be that the valve may not be seating properly. Just trying to get a game plan going on how to resolve this. Is it the valve? The valve spring? The rings?

P.S. I have changed many headgaskets over the years (including a Volvo) so thats not really an issue and I have had heads machined and cleaned so I plan on doing it right. Just trying to figure out my options before I jump into anything.

Thanks in advance for any opinions or suggestions you may have!

---Cory

whoa · Post by **whoa** » 01 Jun 2010, 18:17

Did you test compression with a tbsp of motor oil in the cylinder?

Cory · Post by **Cory** » 01 Jun 2010, 18:23

Negative. I will be testing it again tomorrow after I go to the auto parts store and have them replace the loaner tester that broke after testing 3 of the cylinders (hopefully it just wasnt accurate at any point of testing although #1 was the only one with a low reading). What is the point of the tbsp. of oil?

whoa · Post by **whoa** » 01 Jun 2010, 18:36

If adding the oil dramatically improves compression, it's the rings.

Cory · Post by **Cory** » 01 Jun 2010, 21:11

Great idea!!! Wow I'm dumb. That makes perfect sense and will hopefully help to eliminate the rings as a possible culprit.
Thank you! I will reply with the results as soon as I'm finished.

Post by **jblackburn** » 01 Jun 2010, 21:16

There's also the chance it's a STUCK valve.

The cure for that is to drive the snot out of it for ~5 minutes at high RPM.

Try re-running the compression test though...if your rings were shot, you'd be jetting clouds of smoke out the back.

Cory · Post by **Cory** » 01 Jun 2010, 22:20

No smoke. Just a slightly rich smell at idle but thats it. Ive looked for smoke out of the back as I get on it but nothing (dangerous, I know, but the road was empty and wide).
Ooo...that stuck valve scenario sounds like its more fun than a tedious repair! Im hoping for that!

But how would one diagnose a stuck valve as opposed to a burned one?

Post by **Ozark Lee** » 01 Jun 2010, 23:36

With a burned valve you would register zero compression on that particular cylinder unless the burned area is very, very, small.

...Lee

Cory · Post by **Cory** » 01 Jun 2010, 23:54

Ok got it! I guess we cant really do much speculation until I do the compression testing again, both wet and dry. But from what I have read a stuck valve, or a bent one, would be indicated by checking the valve lash. That may be quite difficult with these vehicles considering the hydraulic lifters and DOHC design but it is something I have done before. Ive owned 2 or 3 or 4 Chrysler Conquests/Mitsubishi Starions (AMAZING cars btw, but money pits. College required me to rid myself of such things.) and converted the hydraulic lifters to solid/adjustable ones on those cars so I have checked and adjusted valve lash before. I know it isnt really plausible to check such things on this car but I guess that option is there if it is even possible?

But like I said it is late and I wont be able to report back and move forward until I have completed the tests tomorrow.

I am kind of expecting to have to replace or send the head off to be re-worked and refreshed. And honestly I am kind of looking forward to replacing the things that go along with a proper cylinder head replacement; timing belt, tensioner, etc. and possibly the PCV system... even though most write-ups say N/A's do not really have PCV problems mine is still leaking oil through the cap and/or valve cover PCV tube (I found oil around #3 spark plug hole today).

Thanks to everyone for your input so far!

---Cory

Cory · Post by **Cory** » 02 Jun 2010, 14:38

Ok so I redid the compression testing (both dry and wet) across all 5 cylinders and these are the results:

Cylinder# dry / wet
1 0 / 0
2 100 / 140
3 120 / 135
4 100 / 140
5 110 / 135

So obviously the number 1 cylinder is dead at idle, I kind of figured that. It explains why the misfire code for cyl 1 keeps popping up. But what should I be looking at now? Is it a burned valve?

And do these numbers look fine for the rest of the motor?

Thanks!
---Cory