juno1

Hi,

I need to do a compression test on my 1980 931, but just want to check on the procedure first, the compression tester did not come with any instructions.

I have tried searching, but the only posts I could find refer to 944's and above, and say to remove the DME relay, which I don't believe I have on this one.

I've just had the engine rebuilt, done about 1200 mile in it and dropped the oil twice, but it's still burning a fair bit of oil and smoking a lot on startup for 5 minutes or so. Just want to see where the compression is at, and how it is after another few hundred miles so I have something to go back to the engine builder with.

Can anyone confirm this procedure?

1. Warm engine to normal running temp (drive around for 20 minutes or so?)

2. Take out all the spark plugs

3. Remove the wire from the + side of the coil (or is it -)? This tester didn't come with instructions for that, and I've only ever done this once before on an old Austin engine years ago

4. Insert the comp tester into the spark plug hole and crank the engine until the guage reads it's highest

5. Repeat the procedure with 10ml of oil squirted into each cylinder for the wet test.

One last quick question, are the $50 leakdown testers on ebay and alike any good for these cars? like this one: http://cgi.ebay.com/ebaymotors/CYLlN...spagenameZWD2V


Many thanks,

PaulStewart

No need to pull the fuel pump relay, just unhook the wire from the overboost switch and make sure it is not grounded. This will shut down the fuel pumps.

Also block the throttle wide open or have the guy cranking the motor floor the gas pedal.

A leak down tester works on any car with spark plugs and is something every serious mechanic should have.

Dennis Wilson

Was the head rebuilt? Bad valve seal and or guides will also cause smoking on initial startup.

Dennis