Low compression in one cylinder

[calab]

I have a 2005 PT Cruiser convertible non-turbo. It's running very rough and throwing a P0304 code - Cylinder 4 misfire.

After some troubleshooting I have found that the compression in cylinder 4 is not good. Dry test is under 40psi. Wet test is 50psi.

Does the compression test indicate rings, or valves here?

My next task is to find my borescope and take a look down the intake manifold and spark plug hole.

[ShermanEF9]

It could indicate a few things. Do a leakdown test to find out where the issue is.

[Sentry]

Sounds like its time for it to have an unfortunate fuel leak and resulting fire and insurance payout.

[calab]

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Sounds like its time for it to have an unfortunate fuel leak and resulting fire and insurance payout.

Naw... Didn't pay much for the car. I bought it for a project, so I expected to have to tear some stuff down.

[mr2mike]

What do you mean by wet test?
Poured a bit of oil in cylinder and tested it?
If so, that# should shoot right up if it's rings. You may have a valve issue.
Bubbling coolant? Oil in coolant? Coolant in oil?

[calab]

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What do you mean by wet test?
Poured a bit of oil in cylinder and tested it?
If so, that# should shoot right up if it's rings. You may have a valve issue.
Bubbling coolant? Oil in coolant? Coolant in oil?

Yes... add a bit of oil in the spark plug hole and test compression. I did see a 10psi increase, and wasn't sure what I should see after adding the oil.

Oil is clean, as is the coolant. No bubbles. Doesn't look like a head gasket issue.

My next move is to get my camera in there, but I'm not sure if I will see anything. I'll be looking down the intake manifold to the intake valve, and down the spark plug hole to see the piston. I doubt I'd see anything useful as far as the exhaust valve - which I'm guessing is the bad part. Sounds like I'm going to have to pull the head at least, regardless of the issue.

Thanks for the help!

[ThePenIsMightier]

I believe the theory is that it the test performed with oil in the cylinder is higher than without, you have leaking passed the rings.

[mr2mike]

If normal is 180 psi. And you only saw a 10 psi increase its more than rings.
Oil would seal the rings for a moment and I've usually seen a 60 psi increase.
It's not good. Leak down testing the one cylinder shouldn't take long. But also, cut to the chase pull head off and see.
Boroscope at this point I think is more for interest.
Head is coming off regardless of what you find.

[ThePenIsMightier]

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If normal is 180 psi. And you only saw a 10 psi increase its more than rings.
Oil would seal the rings for a moment and I've usually seen a 60 psi increase.
It's not good. Leak down testing the one cylinder shouldn't take long. But also, cut to the chase pull head off and see.
Boroscope at this point I think is more for interest.
Head is coming off regardless of what you find.

Yes, I was thinking that only a 10psi bump indicates problems in valves and rings...

[firebane]

Yeah this sounds like a burnt valve or a damaged valve in some way.

Leak down test should be able to give a better confirmation but at 50 psi.. pull the heads.

[ThePenIsMightier]

There is an unfortunate chance that OP is totally fuck.

[firebane]

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There is an unfortunate chance that OP is totally fuck.

Well that happened as soon as they bought a PT Cruiser

[mr2mike]

Good info here: https://www.allpar.com/threads/compr...esults.160593/

150psi is original compression.
What are the other cylinders at?

Also shows a poor boy leak down tester and how to do it.

[calab]

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Good info here: https://www.allpar.com/threads/compr...esults.160593/

150psi is original compression.
What are the other cylinders at?

Also shows a poor boy leak down tester and how to do it.

They were all around 150+ except #4. I'll be checking them again to be sure.

Thanks for the link... Image link to the leak down tester are broken though.

If I end up pulling the head, what parts do I need to replace when I close it back up?
- Head gasket
- Head bolts
- Parts to do any repair, obviously
...anything else?

[ThePenIsMightier]

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They were all around 150+ except #4. I'll be checking them again to be sure.

Thanks for the link... Image link to the leak down tester are broken though.

If I end up pulling the head, what parts do I need to replace when I close it back up?
- Head gasket
- Head bolts
- Parts to do any repair, obviously
...anything else?

I wouldn't replace the head bolts, particularly in a non-Turbo.
Even if they were torque-to-yield, I wouldn't replace them. You can save that money.

[Flexray]

You should find out where the compression is going before pulling the head. This way you have a direction and are not just blindly looking for something.
You could also have a rounded camshaft lobe, or an ejected rocker arm and one of the valves is not opening.

If you are going to pull the head, replace:
Cylinder head gasket kit
Head bolts
Timing belt kit
Water pump
Camshaft seals
Spark plugs
Coolant
Engine oil and filter
Send the head to the machine shop for inspection.

The guy in the link used roloc disks to clean the head/block surfaces. Do not do that. Use a razo blade and gasket remover spray.

[calab]

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You should find out where the compression is going before pulling the head. This way you have a direction and are not just blindly looking for something.
You could also have a rounded camshaft lobe, or an ejected rocker arm and one of the valves is not opening.

If you are going to pull the head, replace:

Thanks for the details. This is the kind of information I'm looking for.

I am not in a hurry to pull the head. I plan on checking everything first. I did have the valve cover off and didn't see any issues, but I wasn't really looking for anything at the time. I will be checking the camshaft and valve operation from there. I would hate to pull the whole head when all I needed to do was pull a camshaft.

[mr2mike]

$40 on Amazon. Can't make one for much cheaper given the parts prices at home depot.
https://www.amazon.ca/Cylinder-Autom...24317179&psc=1

Definitely want to verify the head isn't warped.

[riander5]

You must truly love that non turbo PT to go to these ends for it. And for that, I salute you

[SJW]

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$40 on Amazon. Can't make one for much cheaper given the parts prices at home depot.
https://www.amazon.ca/Cylinder-Autom...24317179&psc=1

Definitely want to verify the head isn't warped.

What's the process of doing this test. I think I want one of these