Fuel pump not coming on, not the relay, fuse, pump, or computers...
 

Okay my fuel pump is not coming on in my 88' 951 project car. I have known good computers in the car, good relays, and a good pump. All have been swapped out with good spares to double check. The pump is simply not coming on, and the fuse is good. Anyone have any ideas?

Could be the speed or reference sensor, can’t remember which one.
I don’t remember exactly, the fuel pump will not turn on until the engine turns 30 rpms.
I believe you can use a jumper on the relay contacts to run the fuel pump.

Check for voltage at the fuse. If you have it there (with the key on) then the problem is between the fuse box and the pump (or the pump itself). If no power at the fuse then it is a DME or realy problem.

I will definately check that tomorrow. I have switched the DME with one out of my own running car along with all the relays and still have not had the pump come on. I have been at the back of the car with my hand on the pump when someone turns the power on, and while turning the engine over and the pump does nothing. Like I mentioned I tried switching the pump out with a known good spare that I have, and even that did not work.
When I first got the car I discovered the DME was not working so I switched it with my good one and have since gotten a replacement but neither make the car start. The previous owner said he was just driving the car and it died on him and could never get it started, which is where I am picking up from in diagnosing this no start issue. But I am having trouble trying to connect why the DME was dead along with what appears to be a no pump issue.

If the pump wont run with a jumper in place of the DME relay then you have a wiring issue.

If it runs with the jumper try checking the factory alarm mine shorted out and no fuel and I installed the jumper per clarks garage and it fired right up

I will try another jumper today when I go outside to work on it. The only question I have about the jumper in place is that I have put two different GOOD relays in the socket, so shouldn't those make it come on if the original relay has an issue?

BTW – an ‘undocumented feature’ of the 944 electrical system is that the power for the O2 sensor is on the same fuse as the fuel pump. If the O2 sensor wires get melted it will pop the fuel pump fuse.
I was doing a quick diagnostic on a car the other day (along with Evil944t) and we wired the fuel pump directly to the rear defroster. That got the fuel pump running.

So I worked on the car some more today and still the fuel pump will not come on. I tried putting a jumper in the relay again and the pump will not come on that way. I also tested for voltage at the fuse and at the pump with the key on and I am not getting anything. I pulled the fuse box up to look for bad wires, looked around under the dash, checked the wiring near the tank and everything looks fine. Does anyone have any ideas of what I should look for or test next?

ign. switch? does everything else power up?

Everything seems to work fine. If I put a jumper in the relay, the water pump for the turbo will start running but not the fuel pump. If I spray some starter fluid into the intake the car will fire right up and run for about 5-10 seconds.

There is a 2 pin wire connector above the fuel filter that connects the small fuel pump harness to the main wiring harness. I' ve found it is a good place to look for an open circuit or a voltage drop

I also tried switching out that harness with a low mileage one that I had, and still nothing. I don't seem to be getting any voltage through any of the wiring to the pump.

When you jumper the DME relay are you connecting terminals 30 with terminals 87 and 87a ?

I used the instructions on clarks garage which said to put the jumper in 30,87, and 87b.