I just had a PPI done on a 348 with 41k miles and here are the results. Compression = 225 +/- 5 psi Leak down 10% 5% 5% 17% 5% 6% 6% 8% Obviously the 17% is of concern, but is it really a problem? I heard a lot of different things about leak down tests and I don't know what to believe. The thing is the car runs and idles great and the compression #'s are all very close. The car hasn't been driven much in the past year and I was told from a ferrari mechanic (with a lot of experiance) that driving it may improve the 17%. He also thought that 17% was not really a problem. What do you think? Any experts out there? TIA
You are looking for a narrow band of difference between cylinders and u have 1 way out and another maginal. Could be sticky rings, could be something else. I might expand on the leak down - search for rifledriver posts on leak down tests - or I'd pass. It is greater concern to me that the 2 cylinders in question are on the same bank.
I am highly skeptical of the results. A 348 does not have enough compression to generate 225 lbs in a compression test. Also no reason is given for the loss in #4. 17% leakage is not hard to trace. Determining the source is part of the job. This test and many like it I read about here makes me wonder what people are paying for. There is never complete information provided. Choosing a person to perform a PPI is very important and it seems it is not often done properly. Your mechanic should be able to provide the answers to your questions and evidently he has not...at least to your satisfaction.
When I did the PPI for my car last year, it was around 180psi with <5 percent variance across all cylinders.
Very very important the mechanic knows what he is doing when he performs leak down tests. Have seen MANY results that have been all over the place, because of an inexperienced mechanic performing the job. Take the car back or call him and tell him to look further into that dodgy cyl.
Mine was done with a crayon. As for an explanation of the results there was some difficulty as nobody else at the dealer's shop could translate from the guy who actually did the testing...but apparently he had extensive experience on diesels, oh yeah! This is why I'll only let experienced techs with recommendations work on my car...
How can an engine physically have a high compression with large leaks? If a balloon has a big leak, will you be able to compress the air inside said balloon while the air is rushing out?! To me, an ordinary Buyer shouldn't even be doing a leakdown test...that's a test to tell engine-rebuilders where to begin. A Buyer should just want good compression numbers from a reliable source.
Both tests are important. They provide different but overlapping information. If I was to do only one it would be a leakdown.
Leakdown is a more detailed test but requires more effort and is also easy to screw up. If the piston isn't at TDC you might get an inaccurate reading. It's not brain surgery, more like rocket science. Just one more reason to pick your mechanic carefully.
I had some screwy #'s as well. From a certified F dealer. Compression in one cylinder of only 110. I took it to my local mechanic, and he said it would not run with compression that low. Who do you trust? The test was repeated at another dealer and #'s were 160's across the board. The car has run flawlessly for 2 years, including a rigorous track session. If it runs well, drives well I would be careful about putting to much weight into a comp/leakdown test.
