Hello. I've had an on going problem with my car for over a year now. 98% of the time it would start with no problem, but once in a while it would crank over but not start right away. It would always start but sometimes it would take 3 or 4 cranks and other times I'd sit for a half hour trying it before it would start. There is no rhyme or reason to it, it happened after a 2 hour drive and after a 2 minute drive. It even happened after sitting over night. On 2 occasions it did'nt start at all so I towed it to my mechanics and both times it started and I drove it off the trailer. I've brought it to my local machanic and to a mercedes dealership and alot of work has been done to it over the past year with no improvement. In fact it is now at my local machanics and it wont start at all.

Heres what has been replaced: Spark plugs and wires, mass airflow sensor, fuel pumps, fuel pump relay, crank shaft sensor, computer (used), wiring harness.

My mechanic said that the computer is not turning on pin 86 of the fuel pump relay and that the coil and injectors are getting power but thay do not cycle. Could the cam sensor cause this?

Any input or opinions will be greatly appreciated. Thank You.

 

it is best to diagnose it when the problem is present.

divide it between fuel and ignition, then eliminate each possibilities.

 

There was a service bulletin on this car for cracked cold solder joints in the overvoltage protection relay. Very hard to catch. I would put one in if the date on the relay matches the year of your car. The relay powers up your HFM (fuel) computer. The injectors are getting power because the computer pulses the ground side.