E30 fuel pump volume test

[potatomash]

Hey guys,

Been having fuel problems recently, and my pump finally gave up the ghost last week. Since then I've put a new pump in (in tank style) and i"ve also got a fuel pressure gauge in the delivery line before the rail.

Started it up and fuel pressure was going down when I gave it revs. Decided to do a volume test and when I jump the pump relay, the fuel pressure goes up but nothing comes out the return line...what does that mean...:???:

[AndrewBird]

Fuel pressure regulator works off of vacuum, so with the engine not running, it is probably closed all the way, hence no flow.

As to why your fuel pressure drop while running, that is likely a bad fuel pressure regulator.

[potatomash]

Hmm ok that makes sense. The bentley says you can jump the pump and catch the fuel out the regulator when the car is off so thats pretty confusing..

Is this expected pressure? This is with brand new regulator as of 10minutes ago... https://www.youtube.com/watch?v=aom_...ature=youtu.be

Always seems to be in the low 30's, which isn't ideal is it? I recently changed the fuel filter, just an aftermarket factory replacement, this couldn't be clogging anything could it?

Ive done voltage tests and they are fine, and amperage test gives 4.6amps at the pump

[bmwstudent]

The regulator will flow fuel without vacuum applied to the port. If you have the pump running and no fuel coming out of the return line i would take the supply line off the rail and check volume there. The regulator is on the return side of the rail.

[potatomash]

Well when the car is off fuel builds up against the fuel regulator cause when I took it off to change it fuel burst out at me. What does that mean..

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[bmwstudent]

It means that the pump is building pressure and the regulator is holding it after shut down, just as it should be. Do you have the line hooked up properly (backwards)? Is the return line clogged? Fuel should enter the rail then exit through the regulator. In other words the regulator should have the return line hooked to it.

[potatomash]

Yea lines hooked up properly. How much pressure needs to hit the fuel regulator for it to spurt out fuel when the car is off..? Return line not blocked but regardless if the return line is clogged it's not going through the FPR

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[bmwstudent]

the return line is after the regulator. I'm surprised you can't get fuel to come out of the return side if the car starts and runs. I'm not sure how much pressure is need to push fuel through the regulator. Have you tried putting the return line into an empty jug and running the car?

[potatomash]

Not yet I guess I'll try that next. I tried squeezing the return line and my pressure gauge didn't go above 50..

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[bmwstudent]

Wear safety glasses, gas hurts.

[potatomash]

Ok so heres what I've now done...

Plugged a hose into FPR, started the car, and collected fuel into a bottle for 30s, got a measly maybe 200-300ml.

Evidence....

Undid the fuel feed line into the fuel rail and jumped the fuel pump relay and got about 950ml.
I then pinched the feed line while doing the above test again and watched the pressure gauge and it didn't get above 40psi.

What does that say...?

[potatomash]

Ok so I did a couple more things.

I put my fuel pressure gauge hose straight onto the pump outlet and ran it into a bottle. Pinching the hose still didnt go above 40psi.

So I put a multimeter into the connector that comes to the pump and it showed 12.3v. When I plugged it into the pump and tested while it was running (fuel relay jumped) it only showed 3-6v and when i pinched the hose that went even lower....

So, I made a fused connection straight to the battery and did the same thing. This time multimeter gave me a solid 12 volts, however pinching the hose the pressure still only got to 50psi....

Firstly, with the car off and the fuel relay jumped, should I expect the pump to run at full 12v or would that only occur when the car is on? That will tell me if I have a voltage problem or not because it seems weird that I have 12v when the pump isn't plugged in.

Secondly, is my new pump crap and should the pressure go higher than 50psi when I pinch the hose? From what I've read a decent pump should about double running pressure (or does that not count because I'm not actually running it through the fuel rail etc)

[e30onBBSs]

I'm not familiar with the voltages but I know a clogged fuel filter can really weaken the pump and surely reduce pressure. I would get a new filter and see if that solves the problem. The worst is when someone gets a new pump and doesn't change the filter and the reason the first pump broke was because it was working 300% harder because of how much gunk was in the filter, and then the second one goes too.

[potatomash]

Changed that about two weeks before the pump. I also tested pressure before and after pump and results were the same

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