Factory Spec: "Compression should not be less than 689 kPa (100 psi)
and not vary more than 172 kPa (25 psi) from cylinder to cylinder."
All of the new engines i've checked are all at an average of
140-150psi.
If the cylinders are all low (at or below 100psi)...either get a
better compression gauge or you've got a very tired engine (or one
heck of a vacuum leak).
- Bernd
On Fri, 03 Oct 2003 06:40:29 -0400, raymond.irons@gm.com wrote:
>
>
><snip> If your reading anything under 100psi, you've found the problem.
>
>Not necessarily so Gary. You're not looking for a minimum pressure reading
>so much as you're looking for relatively equal readings on all cylinders.
>Now if all cylinders are at 50 psi then I start looking for a hole in the
>engine somewhere. The FSM should list the tolerance range for engine
>compression. A new engine may read 125 psi +/- 3 psi on all cylinders for
>instance and that same engine with 200K miles on it, even if it has been
>well maintained, may read 98 psi +/- 5 psi on all cylinders. Does this mean
>this engine needs major repair or rebuild? Not in every instance. If all
>other diagnostic data point to no major problems then is it worth the time
>trouble and expense of removing and rebuilding or replacing the engine?
>Probably not. Now if we take the same engine and do the same compression
>check and find 5 cylinders with 98 psi +/- 5 and one that has 70 psi then
>we've found the culprit in that cylinder. However more diagnostic is needed
>to determine the cause of the low reading and probable repair.
>
>
>Ray Irons
>Dover, DE
>
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