DarrenD

I had an issue last weekend at the track with my 4psi supercharged 944. The car ran amazing but I was having major crankcase venting issues. I was blowing a large quantity of oil out the dipstick hole. I tried a few different way to relieve it but was unsuccessful. So I built by own baffled catch can, installed it and went for a drive. The car isn't running well anymore(wasn't on the way home from the track either). My A/F readings are off, the car won't run in closed loop anymore(might be a fouled O2 sensor, not sure) and it just feels off. I took it for a drive and emptied the catch can when I got home and there was about an 1/8th of a litre in there(after 20 mins of driving). Also the car was running hotter than usual and being that it isn't hot out today that's cause for concern too. Thats a lot of oil for a short drive. So I brought it home and did a compression test. Here are the results:

Cyl. 1 - 160
Cyl. 2 - 195
Cyl. 3 - 160
Cyl. 4 - 160

What is up with cylinder 2?

The spark plugs are all pretty much the same, maybe looking a touch on the light side but I did lean out the tune a little for the drive home. It was still showing under 14.7 minimum on the AFR gauge and going rich at WOT.

Also there is oil at the base of the head under the intake manifold side leading me to believe the head gasket is gone, but in my experience, the coolant or oil would show signs.

I'm stumped. Based on what I am seeing I'm thinking head gasket, but why the increased cylinder pressure in #2?

Thoughts?

Jfrahm

My guess is that it's scuffed and leaking compression into the crankcase.

odonnell

Wouldn't that mean that the pressure reading would be lower than the rest though? Unless the crank case had >160psig of positive pressure for some obscene reason.

DarrenD

That is my thinking too. If I've got cylinder or ring issues, the number should be lower than the other three, not higher right?

I am wondering if I don't have oil leaking into that cylinder somehow and it's giving me artificially high numbers. But why would I have oil in that cylinder?

I'm going to pull the cylinder head off tonight and see what's up? I'm just trying to prep myself before hand if I only need a head gasket or a complete rebuild?

V2Rocket

oil/water in the cylinder, around the edge where the rings go (preventing any blowby whatsoever) might pump the pressure up?

DarrenD

I am thinking oil. Car hasn't used any coolant at all.

But how? Through the head gasket?

thomasmryan

I think you are blowing oil into the intake from the aos.....

DarrenD

I was, I'll agree but now I am running a catchcan inline so no chance of that.

Vincent C.

maybe you hurt the other 3 cylinders and #2 is ok...i would perform a leakdown test and see what you get....good luck....vinnie

carlege

cracked head around valve stem?

thomasmryan

I am having a hard time visualizing how crankcase ventilation works on a pressurized intake.

Van

160 psi is about right for a 10:1 compression ratio. 195 psi is about right for the Euro 11:1 ratio.

What year is your engine?

DarrenD

It's a 1986. Came out of a Canadian car. Not a Euro engine as far as I know.

Van

That should be a standard 10:1 car. I'd expect to see something in the 160-165 psi range.

I wonder if you have excessive carbon build up, or something that is displacing some of the cylinder head volume... this would give you higher compression numbers?

Vincent C.

but the head could of been shaved to raise the compression ratio....we did that on the 44 turbos....still think the leakdown would show something that would lead to pulling the head....