Missionary

Hi Folks,

I am about to change my plugs so I thought I would do a compression test while I am at it. Are there an MB WIS docs on this. I just don't want to confuse the ECU when I am cranking.

Essentially trying to crank without ignition or spark without triggering an alarm. Couple of fuses maybe or does MB have some more elegant form of diagnostic mode?

Merc63

I just cranked mine, remove all the plugs and do the test. I got 180-185psi.

Hold throttle open, not sure if it will open throttles but I did it anyways.

Missionary

Looks like you can do it via STAR based on crank speeds... Anyone know how accurate this is?

roadtalontsi

it's very accurate in comparing one to another. the values it gives you are difference in rpm though not compression. There really is no need to check compression if everything is running fine. Typically unless you are getting a misfire or drivability problems your compression is fine. These cars are very very picky.