Don A

Last week on a very hot day after running fine and sitting for 30 minutes my 2002 C320 would start then immediately stall. It appeared to have no fuel pressure and I could not hear the fuel pump run. I allowed to sit all night to cool but it still had the same symptoms the following day.

The fuse was checked and is good and the relay checks out fine with 12 volts applied it clicks and completes the output circuit (via ohm meter). The fuse has 12 volts supply and the relay has 12 volts to one side of the coil circuit with key on. I do not hear or feel the relay click when the key is turned on or the engine is cranking. I jumpered the relays switched output and the pump still does not run with key on or cranking.

I exposed the fuel pump under the driverside back seat, pulled the 4 pin connector and applied 12 volts to the two outer pins with what appeared to be the power wires (brown negative, green/black positive) but the pump still does not run.

I'm baffled and have a couple questions: Should the pump run with power supplied to these pins? Can anyone post a PDF of the fuel pumo wiring for this cas as the Hynes manual I bought does not include this diagram and the thumbnails I found on this forum of the wiring diagrams are of such poor resolution they are unreadable. I appreciate any help i can get at this time.

The vehicle has approximately 33,000 miles.

Thanks,
Don

Glyn M Ruck

Have you checked the fuel pressure at the front Schrader valve on the fuel rail that connects the injectors? It should be >3.8bar or 55psi while cranking.

Remember at start the fuel pump runs to bring the rail up to pressure & then stops to await cranking.

Don A

I checked the Schrader valve on the fuel rail. When I pushed it I got a dribble. Attempted to crank engine...no fuel at Schrader valve. No fuel pump on key up to pressurize the system.

From the wiring diagram you posted, are you indicating that I have the system 06/01 without an internal fuel pump control module with pressure regulator?

The fuel pump in my car has two connectors. One is a 4 pin (has the power leads black/green pin one and brown pin four) more like 05/01 and a second connector with three wires. I will upload a picture when I get on my computer (this iPad just will not do an attachment on this forum).

The diagram you attached seems to indictate that putting power to pins 1 and 4 should run the pump! I will feel blessed if all I have to do is replace the pump assembly!

Thanks for your assistance,
Don

Don A

Here is the picture i promised...

Don A

I believe I found the problem. I pulled the fuel pump/fuel level sensor module in the passanger side (right side) of the fuel tank and found the coonnector to the fuel pump power was charred and burned (see pic attached). The pump runs when 12 volts is applied.

I am uncertain if i should buy a whole fuel pump module or just repair the wire. My concern is: Is this the primary failure or is this the symptom of another issue? has this been seen before by any of you experienced MB techs. Where can I get a new connector or do I need to replace the whole harness.

I will replace the fuel filter also as I am aware a partially plugged filter can cause the fuel pump to work harder and draw more current (possibly leading to this type of failure).

Any thoughts or advice is greatly appreciated...

Don

Glyn M Ruck

Replace the fuel pump.