Impreza turbo leak down diagnosis help please...

[dern]

Last week I started my my99 uk turbo wagon and blue smoke came out the exhaust. I read up on the possible causes and all of the turbo diagnosis web pages suggested that the air filter becoming blocked could pull oily vapour through the breather hoses so I swapped the k&n for a paper filter just to check that and got rid of all the blue smoke. I posted on this subject last week by the way and someone also suggested that a blocked air filter could do this.

Anyway today I decided to do a leak down test just to make sure the engine was good. I pulled all the spark plugs and they're all lovely and light brown except for number 2 cylinder which is oily. I did a compression test first and all the cylinders produced 150psi except number two which produced less than 50psi. I then did a leak down test and all the cylinders came up with 15% which I think it ok except for number 2 which produced 95% leak down which is obviously not. I get no bubbles out of the coolant and no air noises coming from the air intake or the exhaust. Sticking a rubber hose down the oil filler and the other end to my ear and I can hear air moving in the block. This suggests that I'm getting excessive blow by in that cylinder so I'm guessing either bore wear or piston rings.

I'm getting no unusual noises at all and no oil smoke out the back and the engine runs fine and pulls well. I do have a slightly lumpy idle though.

On the basis of this can anyone confirm my diagnosis of rings or bore wear or is there anything else I can do to test the engine. Also what could my next move be.

My engine has done 84k miles.

Apologies for cross posting this to engines.

Thanks,

Mark

[ScoobieWRX]

At first i was going to say leaky valve stem seals but on what you've said you're probably right.

Pour a little bit of engine oil from a mini oil can down cylinder No.2 and check cylinder compression again. If it goes up and is level with the others then you have definately got piston ring issues. You may have a broken or badly scored compression ring.

My guess is you'll need to pull the engine apart to investigate properly and you'll probably have to rebuild the bottom end, specially with that mileage on the clock. You could just replace a single piston but IMHO i think that's false economy and i would be getting the whole lot done. Bores re-honed and 4 new pistons, job done.

Or you could do what i'm doing just now and that's fitting an STi8 engine in my WRX wagon