What could cause and exhaust valve not to close completly?

[calab]

I've got a PT Cruiser here that is not running well. Compression on cylinder 4 is poor and doing a wet test doesn't improve things (under 10 PSI dry, and just over 10 PSI wet). I'm suspecting that the exhaust valve is not closing.

Without removing the head, what can I check, and more importantly, what could I fix?

If/When I remove the head, is there anything cheap or free that I should be doing besides diagnosing and fixing cylinder 4?

What I'm guessing could be the issue...
- Weak spring not pulling the valve closed (Is there a way to check this without pulling the head?)
- Bent valve jamming before being fully closed (How would that happen?)
- Dirty valve that is being held open by crud where it seals.
- Bad spacing between the cam and valve keeping the valve open (Is this even a thing?)
- VERY bad ring(s) that a wet test doesn't even seal up (This would cause pressure out the oil dipstick tube and filler cap?)
- Head gasket leak (This would cause pressure/bubbles in coolant?)
- Cracked block??? (This would cause pressure/bubbles in coolant and/or blow out the oil dipstick tube and filler cap?)

Never dealt with something this deep or critical, so I'm looking for all the input I can get.

[ThePenIsMightier]

Weak spring seems very unlikely.
I'd bet on a bent valve or a valve seat that's completely ruined.

[gmc72]

They are known to have head gasket issues. My guess is that there is a leak, and/or the head is warped.

[JRSC00LUDE]

Just seafoam it, problem solved.

[ExtraSlow]

Crack and egg into the intake then sprinkle some pepper after it.

[ianmcc]

Smoke test. Will require pulling the valve cover and intake manifold and doing a cheap and dirty smoke test involves putting cylinder no. 4 at TDC with both valves closed. Pull the spark plugs from all cylinders then take a length of hose that you can stick down the no 4 spark plug hole and light up a big smokey cigar. Puff smoke down the hose if any smoke comes out anywhere except back out the number 4 it's a valve or head gasket.

[FunWheelDrive]

You need to borrow or buy a leak down tester, bring cylinder four up to TDC and listen to where the air is leaking. Listen in the exhaust pipe of the car to see if you can hear air coming out of the cylinder. If the intake and exhaust are quiet pull off the valve cover oil filer cap and listen for blow by.

[calab]

Thanks for all the help folks!

[firebane]

Its probably best to not make new threads for each thing. You created a thread previously which could have been used.

[Flexray]

Make a leak down tester out of your compression tester. Take a tire valve core tool and remove the Schrader valve out of the end of the compression tester lead, connect the gauge side to the quick connect on your compressor hose.
This style of tester will connect to "B" type compressor fittings
https://shop.snapon.com/product/Comp...st-Set/EEPV500

If you have a tester that has a threaded on gauge. Take off the gauge use an adapter and thread on a male compressor fitting and connect it to your air compressor. You don't need to know how much air is leaking out, you just need to know where it's going.

You can also remove the intake and exhaust manifolds, turn the engine until the valves are closed. Fill up the ports with brake clean. If a valve is not sealing the brake clean will leak out of that port and into the combustion chamber.

If you think a valve is bent. Remove the camshafts and place a straight edge across the valve tips. If a valve is bent, that tip will be lower than all of the others. If a valve or seat is worn, the tip will be higher than the others.

Weak valve springs will case the valves to not full seat. The exhaust valves will over heat and burn because they cannot conduct heat into the cylinder head properly.