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M113K Compression Test

Najam

New Member
Joined
Dec 19, 2018
Messages
29
Location
Canada
Car
CLS55
Hi everyone,

A bit of background....I bought a CLS55 a year ago and unfortunately the head gasket went.

I didn’t keep too much by way of documentation other than a few pictures and the memory of it being a right pain in the a*se to fix!

Before I fire up the engine I just want to do a compression test. I’ve got the tool and am ready to go.....but I’m not sure how to go about doing it.

The car has basically sat in the driveway while I’ve been fixing it for 4 months on and off.

I’ve read that in order to do a compression test it’s best to crank the engine after disabling the fuel pump and also ensure no sparks are being produced via the spark plugs.

How do I disable the fuel pump and cut the sparks being generated?
P.S. I don’t have a Xentry system to do that and am looking for a way without it.

Does anyone have any suggestions?
 
You must remove all spark plugs and hold throttle wide open during compression test, not sure how to disable fuel pump, relay box maybe
 
Remove injector connectors? Should be easy to get to and if the injector doesn't open then the pump will just pump back to the tank.
 
There should be a fuse for the fuel pump - pull it.
Disconnect the low voltage connections to the ignition coils if possible. The ignition does have to be disabled by whatever method is available as obviously all the spark plugs are removed for compression test. Leaving the HT leads live without the earth return via the (installed) plugs risks damaging the leads/coils/ECU.
Opening the throttle would be better (wide open isn't needed though as not testing at 6000rpm) but if fly-by-wire, could be tricky. Consider disconnecting the throttle body in that case.
 

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