'86 325e fuel system questions

[ascendotuum]

Car is an 86 325e with M52. So the fuel pump appears to have died on me. I have been having severe hesitation issues along with the MPG gauge fluctuating randomly for awhile... then it died completely going down the road and won't start anymore. When I turn the key it just cranks and cranks but won't start. And I don't hear the pump priming itself anymore either.

Now onto the questions. I guess I'm just trying to wrap my head around how the fuel delivery system works. Some of these questions might be stupid but bear with me please. So as I understand it, my early model has two fuel pumps, one low pressure pump in the tank and a high pressure pump in-line underneath the car.

Is there only one fuel pump relay that activates both pumps simultaneously? I'm going to make sure it's not the relay by bypassing it, but when I do this both pumps should start running right?

If it turns out the pump or pumps are bad, should I buy a late model 318i pump and scrap the inline HP pump?

And also, where the hell would the fuel pressure regulator be? In the engine bay and not under the car right? Is it before the fuel rail on the feed line or after the rail on the return line? I can't seem to locate it. I found what looks like a FPR underneath the car, but it only has 2 connections (in and out) and no vacuum connection. I believe this is the "absorber" which I think is unneeded and can just be deleted?

Thanks alot. I gotta get this car back on the road quick as it is my daily driver :(

[justin_l_]

Yes they both should kick on. No they work fine, why change a good thing. It is usually on the end of the fuel rail.

[ascendotuum]

Thanks for that. I was thinking to change the pumps so that I only have one pump. Less to go wrong. And also so I don't have to buy two pumps, haha.

Anyone else have any input?

Sent from my HTC One using Tapatalk

[ascendotuum]

So I've been working on this all weekend. I got most of my problems sorted. I replaced both pumps, fuel filter, new fuel hoses. After all of that I then discovered I had electrical problems that I had to deal with.

The problem now is that the ECU is not triggering the fuel pump relay. Pin 85 on the fuel pump relay is supposed to get grounded by the ECU to energize the relay, but this isn't happening. Why would this be? If I bypass the relay (by jumping 30 & 87) the pumps run and the car starts. Or, if I manually trigger the relay by grounding pin 85 to the chassis, the relay clicks and the pumps run as well.

Before, when I turned the key on I would hear the pumps run for a couple of seconds to prime. But I don't hear this anymore? Someone mentioned that if your crank sensor is bad, then the ECU won't turn on the fuel pumps. But if the crank sensor was bad then the car wouldn't run at all so that can't be it?

[ascendotuum]

So in the E36 electronic troubleshooting manual it says that on the ECU, the fuel pump trigger wire is pin 1. Well, when I look at pin 1, it is the same color wire as pin 85 on the relay, so that's good. But I have no continuity from one end to the other... maybe this is my issue.

I am going to run another wire from ECU pin 1 to relay pin 85 and see what happens...

[ascendotuum]

PROBLEM SOLVED - I ran another wire from ECU pin 1 to FP relay pin 85 and BAM. The relay triggers like it's supposed to and the car starts. Woo! Now I just have to run these wires permanently.

So it would seem that this entire time it was wiring problems...