Compression check

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Thu 8 Nov 2001 13:25
Compression check - Dan J
How can a compression check be carried out on a car fitted with a catalytic converter?

I know you simply remove a spark plug, screw in the meter and turn the engine over but surely this can damage the cat as unburnt fuel is blown out of combustion chamber and into the exhaust?
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Thu 8 Nov 2001 13:48
Re: Compression check - Rob Fleming
A compression check should be done with the engine at running temperature and the coil disconnected - cranking the engine with no spark on a cold start cycle could well cause damage, as well as being a useless test.

The amount of fuel injected into a warm engine at idle is negligible compared to the bucketloads that get past the plugs when you first start it up.

Rob
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Thu 8 Nov 2001 13:55
Re: Compression check - mike harvey
Dan, disconnect the fuel pump or injectors at the most convenient place.
regards, Mike
PS, I also agree the amount is negligable, but leave the plugs out and it will not go down the exhaust anyway.
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Thu 8 Nov 2001 15:32
Re: Compression check - Andrew Moorey (Tune-Up Ltd.)
Carry out the compression test cold. Use a remote starter or jumper wire on the starter solenoid with the ignition off and you don't have to worry about fuel entering the exhaust. Crank the engine for four or five revolutions and note the initial two strokes. You are looking for a minimum of 75psi on a cold engine. Much less than means trouble.
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Thu 8 Nov 2001 16:43
Re: Cold Compression check - Rob Fleming
I stand corrected!

Don't suppose you could point your considerable expertise in the direction of the 'Noisy Tappets' thread I started a few days ago (prob now one click down old messages)?

Thanks in advance

Rob
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