No'2 Cylinder of my '99 turbo only has half the compression of the others. Any ideas?

 

Number of reasons:

Melted & therefore got a gaping hole in it - fuelling issue ie injector down plus many others

pistons rings gone - easier to pop the piston out & see 4 sure......

what compression were you getting? as tolerances are between 140-170 ish....

 

If you have some compression it's unlikely that you,ve got a hole in a piston...sounds more like iffy valve sealing to head, or piston rings worn/broken...You could try taking a reading after adding a small ( few cc's) amount of oil to the cylinder which can create a temporary seal if it's the piston rings at fault. This reading would then usually be greater than when taken before adding the oil.....but won't make a difference if the rings have broken up and left large gaps...
Was the engine using oil?...blue smoke out of exhaust on overrun?...usually points to problem with rings...

Has it been modded,running lean causing a valve or valve seat to get burnt?...leading to loss of compression?....

 

Surely blue smoke on overrun would point to valves? Blue smoke under acceleration pointing to rings?!

Gareth.

 

You've probably done in the piston, melted the edge of the crown causing low compression, either that or it has a burnt valve, no 2 is not the leanest cylinder so its a bit suprising but not unknown. Blue smoke points to oil getting into the cylinder and burning, white/grey means oil is geting into the turbo end, there may be no oil smoke at all but its still going to have a problem in there. There is no way these cars just leak that badly. (assuming the compression test was done properly)

bob

 

Looks like the head needs to come off to see what's going on in there.....

 

I've seen a few melted pistons come out with compressions of 0, 30 & 90 psi, all three were in various states of meltdown. Interesting to look at, though...

 

Interesting...but expensive...I suppose he did say 1/2 the pressure of the others...most piston failures I've seen that are that bad were 30-0!!!....sounds like you've seen some good uns!...Head needs to come off...

 

my no2 piston failed/detonated down the side of the piston.had 4 bar c/r.had broken 2 rings and ring lands,how gutted was I !!

 

Could be gummed up piston rings not sealing.
Spend some time doing an engine flush and replace the oil.

It would be nice to do the check with oil previously mentioned but it won't work on a flat four as you a) can't get the oil in becuase you can't get to it (unless the engine is out) and b) even if you could, the oil will not seal on the top of the piston all of the way around to act as a temporary seal.
If the engine flush does nothing, then you will have to start dismantling.
Mike

 

DON'T put engine flush in a Subaru engine EVER unless you want a big end failure. Engine flush is generally 50%oil 50% paraffin or similar. The viscosity is way too low and serious engine damage will occur.

David API

PS noticed the date of this thread hope I'm not too late.