car starts and dies

[Sandeep Shinde]

Car starts each time it is cranked but dies immediately. Fuel filter is new. Upon investigation the fuel pump cuts off due to the fuel pump relay. If the pins on the fuel pump relay are jumpered the car runs fine. New fuel pump relay did not resolve the problem. Same condition, car starts and dies. The fuel pump relay has a TD input on the electrical diagram. What is this signal and what may cause it not to be present. Also the RPM gauge is not working as it also gets this TD signal. Any help appreciated.

[mpolli]

I don't have knowledge of that specific car but I can tell you my experience with some non-Mercedes cars that had the same symptom. Most fuel injected cars have a safety circuit to cut off the fuel pump if you get in a crash. In my personal experience this was the problem. The start circuit overrides it so you get the symptom you describe. With the old mechanical air flow sensors it was a contact that would wear out. I am not sure what Mercedes used on that one. Hopefully one of the gurus will now tell you what specifically is wrong. Have you searched?

Mike

[david s poole]

this is a voltage put out by the ignition unit that keeps the f/p relay in after start.it is also connected to the tach,the climate control relay, the main computer [i may have missed one]it starts out at approx 10vdc at idle and goes down slowly as rpm's rise.it's possible that the ignition unit has quit sending this signal but still sparks,but more likely that broken wire or one of the other consumers dragging to ground.should be able to identify at inner left fender near ignition box as a green wire with yellow stripe.

[Sandeep Shinde]

Thanks David. The signal is present at the coil as well as on pin 4 of the diagnostic socket, but not present at the F/P relay or other circuits. What is the routing of this signal to these units. I do not have the complete wiring diagram.