rick hesek

Hi,
I would like to do a compression check on a M272 (07 E350) engine and need to disconnect the ignition system.
The reason being, I do not want the engine to start or throw a spark during compression check.
Can somebody point me to a harness connector or some way of disconnecting the coils so I can get compression measurements?

Rick H

kajtek1

Do you have SD?
First they allow simulated compression test, what takes couple of minutes of stroking keys, what sure beats plugs removal and sticking the gauge.
Than better scanner should have actual compression test program that will do it for you.

Russell Ormerod

To do a compression test you need to remove all the spark plugs which means you will remove all the coils too as they sit above the plugs, so there is no way it will spark. Yes you can do it in the SD but the proper way is better. What is the issue? Do u have a rough idle maybe? Any faults stored?

rick hesek

Thanks for the replies.
I'm still getting a misfire on cyl 1 after new coil and plug. P0301. No pending codes.
The last time this happened was 50k miles ago on cyl 2 and on the original head. Compression test revealed 80 psi on cyl 2, all others were 145 +/- 5.
Replaced the head due to inadequately hardened valve guides, which is what caused the leak.
I really don't want to replace the head again but a compression check is a good way to rule out ignition and injectors.