: 94 eldo compression test

02-19-04, 07:08 AM
Performed compression test on my 94 eldorado and came up with 125psi on 6 of the eight cylinders and 145psi 0n the remaining two, is this a normal reading if so why the 20psi difference on two cylinders. Engine runs strong and smooth this is just a curiousity question. thanks to anyone that responds.:cool:

02-19-04, 02:02 PM
I wouldn't worry about it in the least. Compression tests are vastly overrated in my opinion. They can be an excellent diagnostic test to pinpoint where something is wrong but to do the test on a perfectly good engine usually leaves you right where you are at....trying to explain a slight difference in some cylinders.

I would say that the readings are plenty close together. There are so many variables that affect a compression test that it is hard to duplicate readings and surprising that some cylinders were even as close as what they were... Carbon build up , cylinder temperature, cranking speeds, valve seating, slight carbon deposits on the valve seats, etc. will all affect the readings and could show some cylinders higher/lower than others.

Treat a compression test as just a general measure of the engine's health...if it has compression in all cylinders...then GOOD. Otherwise, don't agonize over a passenge car engine that has slightly different compression in some cylinders. It will probably change the nest time you check it.

If you REALLY want to pursue it I would recommend a cylinder leak down style check where you pressurize each cylinder thru the spark plug port. This test is more repeatable as it eliminates the cranking speed variation, etc... and, more importantly, it will let you hear (by virtue of the air leaking hissing noise) where the leak is..i.e..into the crankcase(rings...listen at the PCV port), the exhaust valve (listen at the tailpipe), intake valve (listen at the throttle body). That will let you narrow the search to what you might want to pursue or generate some ideas to explain the difference in the compression readings.