1984 BMW 733i

[mikeman578]

I have a 1984 BMW 733i that won't start. When the ignition key is turned the starter motor cranks the engine over just fine. I took the fuel line off of the fuel pump and noticed I wasn't getting any fuel. The fuel pump is working just fine. Might the fuel pump relay be bad? I have found a lot of bad information on the location of the fuel pump relay online and am not sure as to where it is located. Does anyone know where it is located? Thanks, Mike

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A side note: I bench tested the fuel pump when I removed it from the car.

[Rudolph320i]

Verify if the fuel pump is coming on when you crank the engine.

[mikeman578]

Verify if the fuel pump is coming on when you crank the engine.

Well the fuel pump is not coming on when the engine is cranking. That's what lead me to believe that the relay wasn't working properly. However, now I tried jumping the solid red wire and the green(with violet tracer) wire in the fuel pump relay socket and I'm still not getting power to the pump. I'm not quite sure how to proceed. Any suggestions?

[Rudolph320i]

IF you dont have power at the relay socket, follow the circuit back to see where it could be broken. Another thing to do is check for spark. If you have neither spark nor fuel then I would look to the crank sensor.

[CMG]

Look in the e23 section there was a thread about it with pics of the relays to check and other stuff

[mikeman578]

IF you dont have power at the relay socket, follow the circuit back to see where it could be broken. Another thing to do is check for spark. If you have neither spark nor fuel then I would look to the crank sensor.

Ok thanks, I'll check it out.

[Avec]

Had a similar issue with my 533 Turned out it was the Main Relay. The wires running to the relay became loose. Actually came loose while driving. I thought I had run out of gas. Reconnected the wires, and good to go.

[mikeman578]

Had a similar issue with my 533 Turned out it was the Main Relay. The wires running to the relay became loose. Actually came loose while driving. I thought I had run out of gas. Reconnected the wires, and good to go.

OK thank you guys. However, now I have a new problem. After playing with the relay and the wiring to the fuel pump I now have power to both fuel pumps. I disconnected the fuel line after the inline pump and verified that I was getting fuel. I am also getting spark in the ignition system. If I spray staring fluid into the throttle body I get ignition but the engine will only run for about 10 seconds until the stating fluid is gone. I would assume that the fuel injectors are operating properly at this point right? I'm not quite sure why the engine will not continue to run. Any ideas?

[Rudolph320i]

You may not have proper fuel pressure to keep running.

[mikeman578]

You may not have proper fuel pressure to keep running.

I opened up the small valve/filter piece that looks like a hat that is located on the fuel line just before the fuel rail and noticed that there was no liquid fuel present. Might this hat valve be clogged or blocked or might there just not be enough pressure to get fuel to this point?

[Avec]

I would saw rear the fuel pressure, but it sounds like zero. Jump the pump relay and test the pressure, or at least are if fuel comes out of the line

[mikeman578]

I would saw rear the fuel pressure, but it sounds like zero. Jump the pump relay and test the pressure, or at least are if fuel comes out of the line

OK I've made some progress. When I crank the engine over I'm getting fuel pumping out of the in-tank fuel pump. At the same time the inline pump is coming on as I can hear it and feel it vibrating. However, while it is running as such it is not pumping any fuel out of it. I took the pump off and ran a fuel line from a gas can and hooked the pump straight to a battery and got fuel to pump out. Does this sound like the pump is not grounded properly and thus not getting proper voltage?

[Rudolph320i]

check voltage at the pump, but sounds like it may be on the way out.

[mikeman578]

check voltage at the pump, but sounds like it may be on the way out.

Ok, new scenario. I now can get the car to start and run if I hook the fuel pump straight to a second battery while a helper is cranking over the engine with the key. Obviously I'm not getting proper voltage to the leads going to the fuel pump. My question now is how do I wire power from under the hood straight to the fuel pump in order to correct this issue?

[Rudolph320i]

you cant just wire power straight to the pump, you need to find out why power isnt getting there.

[mikeman578]

you cant just wire power straight to the pump, you need to find out why power isnt getting there.

OK, any suggestions on how to diagnose that? I'm not the best with electrical.