1972 280SE 4.5L fuel pump now doesn't have voltage-looking for diagram - Mercedes-Benz Forum

 
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post #1 of 4 (permalink) Old 11-06-2006, 07:43 PM Thread Starter
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1972 280SE 4.5L fuel pump now doesn't have voltage-looking for diagram

I have been struggling, one step at a time, to get fuel to my fuel rails again. After replacing the gas filter, fuel filter, fuel lines, fuel regulator, cleaned injectors, and now a tired fuel pump, somehow I've lost voltage to my new fuel pump. The old one would hum and then cut off, but I've got no voltage to the leads now. I have no idea how that happened. I do have the wire taken off of the ignition, but I don't believe that it is in the circuit. And, I'm pretty sure the key only had to be in the 'run' position to get the 12V to the fuel pump.

I've read the link from nutz4benz, but I don't have a diagram that shows where the various pins are at to test the fuel pump relay and fuses. Is there a diagram that is available online somewhere? I've looked at all of the fuses in the engine compartment, as well as the fuse in the driver's foot area, and they look fine. I believe that the fuel pump relay is the one closest to the engine wall, but I'm not sure. And, like I said, I haven't seen a good wiring diagram to help troubleshoot.

Any suggestions?? Thanks again everyone for your assistance!
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post #2 of 4 (permalink) Old 11-07-2006, 08:01 AM
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Hi, The ECU shuts off the pump after about 3-4 sec's if the engine is'nt running.
Fuel flow really does'nt happen much unless the engine is running ,the pump with regulator will just maintain pressure in the rail(s).You want to expect approx. 28 psi. Hope this helps you.kdm
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post #3 of 4 (permalink) Old 11-07-2006, 08:04 AM
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Also, you might try applying 12 volts directly to pump and continue trouble -shooting from there.kdm
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post #4 of 4 (permalink) Old 11-07-2006, 08:11 AM Thread Starter
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I've unhooked the return lines at the ends of the rails and put the hoses into two containers. So, the pressure hasn't built up.

I also removed the last fuel pump and hooked it directly to a battery, and that's how I found out it was not working properly anymore. It would start and then slow down. I now have a new pump.

The problem is that with the key in the 'run' position, when I put a multimeter on the fuel pump, I'm not getting any voltage. That's why I need to find out where/how to jumper or get voltage readings from the pump relay and fuse area under the hood. Another link references various pins, but I don't have a diagram that labels those pins.
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