Really low compression on one cly.

[MiataPaul]

OK so I got my car that I was told needs a new head gasket. It is misfiring bad. I can disconnect the fuel injector and it makes no difference in the idle. I ran a compression test and here are the results:

CLY 1 185PSI
CLY 2 60PSI
CLY 3 185PSI
CLY 4 165PSI

So my question is is 60 psi normal for a bad head gasket or does it sound like I may something worse than just head gasket? I was expecting to see a bit less of a difference. I know there is really no telling till I get the head off, but was looking to see if I should just start looking for a replacement motor.

Also would it be a folly to just replace the driver side head gasket? It is getting cold and my auto cross tires on my Miata are getting mighty stiff, and I cant even imagine trying to drive it with some snow on the ground. The auto parts guy said why change both? I figure it will save a days worth of work.

[555BCTurbo]

You probably have a burned valve with that low of compression

[Arctic Assassian]

Normally a hg leak will affect two cylinders, not just one. now that youve done a compression test, do a leakdown test. Get that cyl. to TDC and use a compression tester hose, and hook some compressed air to it. Now, stick your ear to your intake, exhaust, oil and coolant. If you see bubbles, or hear a hissing noise, you'll know what system specifically to check. If you hear it from the exhaust, you prolly have a bad exhaust valve. If you hear it from the intake, then intake valve. Oil is usually bad rings, but could be headgasket. if your coolant is bubbling, then its your headgasket. that is a really easy way to tell.

[MiataPaul]

Yea it was the exhaust valves. Getting it all put together now. I had some cash flow issues over the holidays! (big surprise there!)

[Arctic Assassian]

word.

[MiataPaul]

I got it together. Stayed up Sunday night after I dropped the kids off at their mothers till 5:00 AM then realized DMV was not open on Monday due to MLK. I even spent the whole weekend talking all about him to my kids, and it never crossed my mind. It would not start then I looked into the back and saw the cover for the fuel pump cover was open! Forgot to plug it in. At least I built up a lot of oil pressure. It seems to be running really good. Only issue I had was the timing belt marking was in between the marks so I counted cogs. I think one of the valve cover gaskets is leaking a bit, no biggie there.

[Arctic Assassian]

Fix that valve cover now. Trust me. Do it!