Hi, just a quick update. So I replaced the Crank Sensor, no change. Also installed the one from my ml500 (same part) but no change. I changed the Cam Sensor with the one from my mercedes (same part) and no change. Going to test the crossfire crank sensor and cam sensors in the merc on sunday. I checked for volts with ignition on at the cam sensor wiring, and seemed ok. The cam sensor wiring plug is toast though - the clip was brittle and broke and the outer casing broke too when i was depressing the tab. Didn't trace it back to the box yet or remove the RCM, but will. Crank Sensor plug was fine though, easy to unclip and nothing brittle. Checked the 200 and 50 Amp inline fuses in the box next to the battery, and those tested fine. I don't think fuel pressure is the issue, strong smell on fuel when trying to start a few times. Didn't get a chance to remove a plug to check for spark, but will Tuesday but I am pretty confident the answer will be no spark. I did noticed after the failed start cycle, a few seconds later, an opening and closing noise emitted from or around the MAF. Going to buy a good merc scan tool, would that be the better way to go before pulling the rcm out? I thought the RCM was more for Fuel than ignition??? Oh and tested the 2 control fuses in the box where the RCM is. Those weren't blown. Being a merc motor of the same era as my ml500 just minus 2 cylinders, I would think it would come up with a start error on the dash. I have seen this before intimidatingly on the ml500 but seem to have sorted that. Crossfire doesn't show anything actually wrong. Tighed1, what does the Fuel Relay do?