Question about Replacing Piston Rings

[hav0c]

I just want to get some opinions about my situation. I have a 2000 Jetta GLS that has lost compression on cylinder 6. The other 5 cylinders have great compression. The car only has 107,000 miles. I haven't even taken it apart yet. I just need to know what could cause loss of compression besides bad piston rings. Can compression loss be due to a valve problem? And how would I test for this?

If it's a valve issue, I've searched and searched for a DIY but can't find one. I've never done valves, should that be left to a professional?

[GTIVRon]

Disconnect the exhaust right at the downpipe, that should be enough. Take your intake elbow off.

Now hook up a leak down tester to that cylinder. Listen for where the leak is. If you hear it coming out at the downpipe, exhaust valve. If you open the throttle body and hear it there intake valve. If you hear it coming out of the dipstick hole, then its either the rings or the valve guides/seals.

I'm not aware of a way to tell whether it's the valve stem seals or the rings without at least pulling the valve cover off.

[hav0c]

I think that's exactly what I needed, thanks! That will tell me whether it's a valve issue or ring issue.

[Scotty_2.0]

Disconnect the exhaust right at the downpipe, that should be enough. Take your intake elbow off.

Now hook up a leak down tester to that cylinder. Listen for where the leak is. If you hear it coming out at the downpipe, exhaust valve. If you open the throttle body and hear it there intake valve. If you hear it coming out of the dipstick hole, then its either the rings or the valve guides/seals.

I'm not aware of a way to tell whether it's the valve stem seals or the rings without at least pulling the valve cover off.

Couldn't have said it better myself

A compression test is the first step, and gives more of a "dymanic" health test while the leak down is a static test that will tell you EXACTLY where the leakage is coming from. You can even have decent results on a comp test but still have valve sealing issues that can even show up as misfires at idle.