Turning the ignition key in my 73 450 SL, the fuel pump activates for about 5 seconds,turns off and the engine starts innediately and runs great.
Turning the key imy 72 350 SL, the fuel pump turns on and stays on and sonetimes the engine starts and sometimes doesn't start at all.
I've replace the fuel pump and filter, rmain and fuel pump relays ...no change..... any advice ??? (The car did not run for 2 years before I replaced the fuelpump)

edco

On the US spec 350SL, the relay/ecu is set up same as your 450SL - fuel pump comes on when you first turn key but then shuts down until you crank the engine. Some people jumper the relay so that pump stays on all the time. Nothing really wrong with that - It is only safety for the pump to only run when engine is running (stops fuel in case of accident for example).

Maybe first step would be to do a fuel pressure check. (tee into fuel rail hoses either on line going to cold start injector or hose at front of engine. Any cheap gauge will do. You should have about 29psig. If that is good, try a fuel flow test (disconnect fuel return hose after Pressure valve and damper and run into a container. You should get ~1 litre in 30sec. if your new pump meets the MB spec.

After that, you might go through one of the trouble shooting guides. There is one in the shop manual. I will attach another that might help.

Attached Files

Troubleshooting.pdf (147.8 KB, 416 views)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5