I answered this in the Tech forum, but this is a better place for it.
BTW Mach4, are you sure the engine rpm is sensed from the tach? From memory (which is not always good!), I seem to recall that the djet ECU gets that from the trigger points.
Quote:
Originally Posted by sallyles4645
My 1972 350sl won't start. I check to wires to fuel pump, not hot. If I run a set of jumpers back to the fuel pump it will start, and the wires that I disconnected are now hot. There is something stopping the motor from starting and allowing the fuel pump to start pumping. In a perfect world the car will start and 2 or 3 seconds later the fuel pump gets 12v to keep it running. Any help would be great.
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First of all, you only get 12V to your pump for a second or two after you turn key on. To check if you have power to pump, you would have to jumper the fuel pump relay. Or connect meter to pump and have someone turn ignition key on while you watch the meter. It should just show 12V briefly.
If after testing you still don't have power to pump, then ...
There are two items that control power to fuel pump.
A fuel pump fuse.
A fuel pump relay.
Fuse is just one of those in fuse box. 8amp, I believe. Forget which one.
Relay is one in pic below (located above fuse box) You can switch it with one of the others (they are all the same) and see if you then get power to your pump.
