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Old 08-09-2011, 08:53 PM   #1
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Default Compression and Leakdown numbers.... need input please!!

So here's the story, my 90 gradually started smoking after I overheated the bjesus out of it one cold morning about a year and a half ago. I just dealt with it for a long time, but it gradually got worse (go figure).

So it got bad enough recently that it was time to start diagnosing. Did a compression test, #2 cylinder was about 120 psi low. The rest were all w/in high end of range. Repeated test wet, no change on #2, so I deduced I had a valve issue. Bought a rebuilt head. Installed that and re tested. Compression great on all cylinders! So i thought i had solved my problem.

But alas, the car was still smoking. So onto culprit #2 - the turbo. Found my outlet pipe full of oil. So turbo seals were shot. Bought new turbo and installed. Guess what? Car is still friggin smoking!!

So other day I bought leakdown tester from HF and tested........ not good......

So my question is this; with the compression numbers I have, and the leakdown numbers, does it shock anyone that I am smoking a quart of oil every 200 miles or so???


Compression

1 - 189 dry / 215 wet
2 - 185 dry / 205 wet
3 - 191 dry / 209 wet
4 - 203 dry / 222 wet

Leakdown

1 - 34%
2 - 39%
3 - 31%
4 - 28%


I realize my leakdowns are not good from what I have seen on the boards here, but I'm just curious if I could still have some other problem besides my rings to be losing THAT much oil. I have never seen a spot of water in the oil or vice versa. Car runs great with the new head and turbo, but still putting out the spy hunter smokescreen.

I vented my PCV to atmos, so not losing anything there. My oil pressure reads up around 63ish under hard acceleration, which seems to be "normal" from what I have seen in other posts. Is there anything else i'm overlooking or is it just my rings are so toasted that they are allowing that much blowby?

Any input is appreciated!
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Old 08-09-2011, 09:15 PM   #2
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With a leak test it's easy to diagnose the leakage. Get a stethoscope, pressurize the cylinder, then put the stethoscope probe in the exhaust pipe, intake plenum, in the radiator cap hole, or in the dip-stick hole. Loud hissing will tell you where the air is leaking. At 30%, something is really wrong.
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Old 08-09-2011, 10:04 PM   #3
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Listening in the exhaust pipe is an urban myth. The muffler muffles the hiss.

Better to listen to the spark plug holes of the other cylinders to check for intake or exhaust valve leakage. (And of course the oil filler cap)

When testing #1, which in TDC firing:
#4 will be in overlap and both valves will be open. (#1's "complement")
#2 will be in BDC with its exhaust valve open. (before #1 in the firing order)
#3 will be in BDC with its intake valve open. (after #1 in the firing order)

So if you hear a hiss in the #4 and #2 spark plug holes, but not #3, then you have an exhaust valve leak.

And so on, given the firing order.
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Old 08-09-2011, 11:05 PM   #4
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Quote:
Originally Posted by JasonC SBB View Post
Listening in the exhaust pipe is an urban myth. The muffler muffles the hiss..
It's worked for me before, but we're going in the right direction.
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Old 08-09-2011, 11:29 PM   #5
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OK well maybe my muff is bigger than yours.
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Old 08-09-2011, 11:50 PM   #6
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OK well maybe my muff is bigger than yours.
It's highly likely. I used my Polish det cans and could clearly hear air passing through.
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Old 08-10-2011, 01:47 AM   #7
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ok, I did forget to mention that part in my original post.... I did listen at the various leak points. All 4 cylinders resulted in hiss in in the oil filler cap hole.. So that would be rings right? Assuming the air is blowing down past the rings, into the bottom end, and then escaping up through the oil ports in the head??.. I did not hear audible hissing at the dipstick tube, the exhaust, or around the intake (but for the intake I just used a stethoscope up against the intake charge tubes where they go into the head- so not sure one could hear audible leak that way or not?).

Since it is a rebuilt head, I'm not expecting I have a valve issue anymore..... altho I guess there are likely some bad rebuilds....
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