not really a silly question at all. i don't see that it would make a difference - if you're cranking it over by using the starter, (and assuming you pulled the fuse for your fuel pump, right?), no damage. you're just building up pressure in the other cylinders, and then releasing it when the valves open up.

GM says yes, I guess the reason is because the engine would turn over at a higher speed. That said, I don't know what, if any, effect that would have on the actual PSI reading versus only attaching the guage to 1 cylinder with plugs in all the others.

Cheers,

If I remember correctly you are also supposed to lock the throttle open so the plates don't restrict the filling of the cylinders...

Rob

To the best of my knowledge the 3 things required for a proper compression test are: #1) engine good and warm(operating temp may be recommended but that can be a bit toasty to work on). #2) all spark plugs removed.The engine has to spin fast enough to give a good reading and plugs in put extra load on the battery. #3)throttle plate blocked wide open so the engine can breathe.-------Also helps to pull the fuel pump fuse and use a compression tester that screws into the spark plug hole and on the threaded adapter that screws into the spark plug hole don't overtighten and destroy the o-ring.

All that is interesting, but my problem is I think I my transmission is going and I want to know if it is worth rebuidin the tranny if my engine is on social security. Has anybody got actual readings.........please.

Uh, sorry. What Foghorn has posted above is the only reference I see for compression readings

I think that we collectively think your readings are good.

Engine Compression Test
Tools Required
Compression Tester

A compression pressure test of the engine cylinders determines the condition of the rings, the valves, and the head gasket.

1. Run the engine until it reaches normal operating temperature. The battery must be at or near full charge.
2. Turn the engine OFF.
Important
Remove the Powertrain Control Module (PCM) and the ignition fuses from the I/P fuse block.
3. Disable the ignition.
4. Disable the fuel systems.
5. Remove the spark plugs from all the cylinders.
6. Remove the air duct from the throttle body.
7. Block the throttle plate in the open position.
8. Measure the engine compression, using the following procedure:
A. Firmly install the compression tester to the spark plug hole.
B. Have an assistant crank the engine through at least four compression strokes in the testing cylinder.
C. Check and record the readings on compression tester at each stroke.
D. Disconnect tester.
E. Repeat the compression test for each cylinder.
9. Record the compression readings from all of the cylinders.
--The lowest reading should not be less than 70 percent of the highest reading.
--No cylinder reading should be less than 689 kPa (100 psi).
10. The following are examples of the possible measurements:
--When the compression measurement is normal, the compression builds up quickly and evenly to the specified compression on each cylinder.
--When the compression is low on the first stroke and tends to build up on the following strokes, but does not reach the normal compression, or if the compression improves considerably with the addition of three squirts of oil, the piston rings may be the cause.
--When the compression is low on the first stroke and does not build up in the following strokes, or the addition of oil does not affect the compression, the valves may be the cause.
--When the compression is low on two adjacent cylinders, or coolant is present in the crankcase, the head gasket may be the cause.
11. Remove the block from the throttle plate.
12. Install the air duct to the throttle body.
13. Install the spark plugs.
14. Install the Powertrain Control Module (PCM) fuse.
15. Install the ignition fuse to the I/P fuse block

My 95 SSEi has the following measurements as of Mid Febuary '05 :

#1 - 145psi
#2 - 142psi
#3 - 145psi
#4 - 135psi
#5 - 140psi
#6 - 145psi

Your readings seem nearly fine to me, but i agree that you should perform a wet test (oil in the cylinder before testing) to narrow down the cause of your lower readings in that one cylinder. If the wet test brings the numbers back up to unison with the other cylinders, its almost garaunteed to be worn rings. If it does not change, chances are the valve seats are worn and they aren't sealing when closed on the compression stroke OR the head gasket is on its way out, which would carry a nice lil' bill along behind it... Good luck with it though, honestly i wouldnt worry about it much though..

The tranny recently gave up in my Bonnie , and i decided to fix it as i have already invested nearly 4 grand into a car which i paid $5000 Canadian for, (brand new entire fuel system including injectors, gas tank, lines, rails etc. totalling aprox $1800) $1000+ HUD windshield, $600 in tires, $1000+ in paint, and now a $1400 (a steal in my eyes) full rebuild on the transaxle is underway. Why waste a car with already so much invested, when a little more invested would bring it near show room condition.

The near future holds in store an M62 rebuild, and the distant future i will consider a full engine rebuild to bring her back to mint condition asides from the front end clunk which no garage can seem to be able to figure out!!! After all this come the mods

Oh BTW it has 192000 or so km'*. So anyway my point is, if you really care about your car, chances are you will keep it and invest more into it like i did. Keep the BonnieClub GOING STRONG!!!

Matt

Wow, you guys seem a little low, I got 165-167psi in August. 5 & 6 were the low boys.