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Registered User
Join Date: Jul 2011
Location: Indianapolis, IN
Posts: 24
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low compression & low leakdown test results on '90 c2?
Hi all,
I'm considering the purchase of a '90 c2 cab w/ ~90k miles on it. The car looks good in pictures, etc. and the maintenance history I have gives me the feeling that the car was well taken care of. I'm in the process of getting a PPI done on the car now and the compression & leakdown test results don't make any sense to me. I spoke to the mechanic today who said he had finished testing 3 cylinders. Compression on each was 125PSI and leakdown was zero on 2 cylinders and very small on the other (<<5%). The compression seems VERY low to me based on the compression ratio of the engine and typical results I have found through searching this site (among others). The car is not local and I have not test driven it yet. I don't believe the engine has been rebuilt & pistons are stock to the best of my knowledge. What questions should I be asking? What could be the cause of such low compression readings? Thanks in advance! -john |
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07-07-2011, 07:18 PM
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Registered
Join Date: Sep 2006
Location: Auckland NZ & Newcastle AU
Posts: 491
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If the compression was tested whilst the engine was cold, it could give you those low readings - ask your wrench?
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Regards, Peter 1992 928 GTS 1993 964 Carrera 2 Coupé |
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07-07-2011, 07:40 PM
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Registered User
Join Date: Jul 2011
Location: Indianapolis, IN
Posts: 24
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since they were able to chat w/ me after testing 3 cylinders, the engine could have definitely been cold. if it was cold, should i have them redo the test? it would seem to me that cold compression & leakdown could give misleading results...
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07-08-2011, 02:52 AM
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Registered
Join Date: May 2005
Location: Houston
Posts: 5,465
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Depends on the gauge being used, use 10 gauges you get 10 different readings. So long as the delta is +/- 5 to 8psi per cylinder across all 6 you are good. The key with compression is cylinder consistency as opposed to say 160psi. I have two compression gauges at home and their both will produce different readings on the same engine.
BTW leakdown seems fine. A 90K 964C2 engine is barely broken in...TONS of life left in that badboy! Yasin
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Ole Skool - wouldn't have it any other way |
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07-08-2011, 03:14 AM
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Platinum Member
Join Date: Jul 2001
Location: Leave the gun. Take the cannoli.
Posts: 20,883
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I don't believe 0% on a 21 year old, 90k miles car......
Is this the seller's mechanic or did you get it to an independent? |
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07-08-2011, 05:57 AM
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