no fuel pressure at engine

[rjd2]

Hey folks, so a few weeks ago, my Delorean started to stutter around 4k RPM when I was driving it. That went to 3k, then 2k, and at that point, I pulled over in an off street location. The car died. For about a year, the car would take a very long time to start if cold. Probably 20 seconds or so of cranking, but it would then run fine, all the way out to 5500RPM ish.

I put a fuel pressure gauge at the engine, just downstream of the fuel filter hose. I replaced the RPM relay, and the fuel filter. I now get zero PSI when cranking at the gauge. I have bypassed the RPM relay, and I can hear the whine of the fuel pump when jumpering the two wires at the RPM relay connector(brown to white/purple). The only things left that I can think of are the accumulator and the fuel pump (all elements in the fuel delivery system are either brand new, or rebuilt, so this is a 2 year old GM style fuel pump and a brand new accumulator).

Is my next step to bypass the accumulator, to test which item is the problem? What is my next step here? Thanks for the help folks!

[Jonathan]

Hey folks, so a few weeks ago, my Delorean started to stutter around 4k RPM when I was driving it. That went to 3k, then 2k, and at that point, I pulled over in an off street location. The car died. For about a year, the car would take a very long time to start if cold. Probably 20 seconds or so of cranking, but it would then run fine, all the way out to 5500RPM ish.

I put a fuel pressure gauge at the engine, just downstream of the fuel filter hose. I replaced the RPM relay, and the fuel filter. I now get zero PSI when cranking at the gauge. I have bypassed the RPM relay, and I can hear the whine of the fuel pump when jumpering the two wires at the RPM relay connector(brown to white/purple). The only things left that I can think of are the accumulator and the fuel pump (all elements in the fuel delivery system are either brand new, or rebuilt, so this is a 2 year old GM style fuel pump and a brand new accumulator).

Is my next step to bypass the accumulator, to test which item is the problem? What is my next step here? Thanks for the help folks!

There isn't much between the fuel pump and where you said the gauge is. Just the filter and the hard lines. Seeing zero psi after the filter tells me either the filter or one of those fittings or hard lines is plugged, or the pump isn't producing any pressure. It shouldn't be related to the accumulator if you're seeing zero pressure after the filter, as the accumulator is downstream of all of this and on the way back to the tank.

I would be inclined to think it is a problem at the tank and / or with the pump. Perhaps the suction side of the pump specifically? Hearing the pump running could be a good sign to tell you the electrical side of things checks out. But it doesn't say for certain it is actually pumping any fuel and producing pressure. Again, if there was something blocking the suction side of the pump, it would sound like it's doing something, just not actually moving fuel.

Even though it's messy getting to the inside of the tank, I would suggest checking on the fuel pick-up hose and assembly and see if something isn't right there. I mean, in a perfect world you could move your pressure gauge around to all the different points and confirm where the first place is there is no pressure, but with what you've described, I'd say it's the suction side of the pump.

[Bitsyncmaster]

I don't think the accumulator would leak enough fuel into the return line even if the "bladder" in side was ruptured. I have see a fuel filter completely plug the fuel. And since you saw it getting worse, the fuel filter is the first thing I would replace.

[rjd2]

I don't think the accumulator would leak enough fuel into the return line even if the "bladder" in side was ruptured. I have see a fuel filter completely plug the fuel. And since you saw it getting worse, the fuel filter is the first thing I would replace.



thanks folks. not sure if it got lost in the shuffle, but when I replaced the RPM relay, I also replaced the fuel filter. so it seems next to impossible it's the fuel filter.

so to clarify, the accumulator is on the RETURN side of the fuel system, not the delivery side?

is there a way to remove the fuel pump and see if it is working? Thanks for the help!

[Rich]

so to clarify, the accumulator is on the RETURN side of the fuel system, not the delivery side?



Yes and no.

The pressure end of the accumulator is the bigger end with two ports side by side.

The return (low pressure) end of the unit is the smaller end with the single port. The port on that end side normally acts as an air vent to the tank when the internal bladder gets pressurized by the fuel pump. It has a secondary function - returning any fuel that bypasses the internal bladder and routes it to the tank if the bladder fails (leaks).

[Bitsyncmaster]

thanks folks. not sure if it got lost in the shuffle, but when I replaced the RPM relay, I also replaced the fuel filter. so it seems next to impossible it's the fuel filter.

so to clarify, the accumulator is on the RETURN side of the fuel system, not the delivery side?

is there a way to remove the fuel pump and see if it is working? Thanks for the help!

I think that one fuel filter that failed, something went wrong inside it. I just did not believe a fuel filter could completely plug the flow, but it did. If you pull the hose from your pump, you can run it into a bucket to look for good fuel flow. Checking pressure dead ended at the pump should be greater than 100 PSI. So make sure your gauge is rated higher.

[Bitsyncmaster]

Yes and no.

The pressure end of the accumulator is the bigger end with two ports side by side.

The return (low pressure) end of the unit is the smaller end with the single port. The port on that end side normally acts as an air vent to the tank when the internal bladder gets pressurized by the fuel pump. It has a secondary function - returning any fuel that bypasses the internal bladder and routes it to the tank if the bladder fails (leaks).

Correct.

That small return pipe is why even with a bladder rupture you still should get fuel pressure. It acts like an orifice.

[rjd2]

thanks. so right now, i have fuel pump>accumulator>brand new fuel filter> fuel pressure gauge. and i have zero pressure at the gauge. it can't be the new filter, and it can't be the accumulator, so the only thing left is the pump. is there a way to test a GM style fuel pump in isolation? as stated, i can hear it run. should i remove the fittings and run clear hoses to the nipples and see if i get fuel when it runs? is there a better way to test it?

[dn010]

You can use any good fitting hose on the output nipple and run the hose into a container to see what you're getting out of it. The obvious fire hazard warnings apply.

[Rich]

While you?re looking at the pump?s output and pressure it may help to know the voltage across the pump wire +/- leads while the pump is running. I know you can hear the pump.

Test it as close to the pump as you can.

[rjd2]

welp, i'm a full blown idiot. the fuel gauge wasn't working properly. all my mechanicals were sound. the car just needed....fuel.

but now i need to figure out why my gauge reads just above the quarter tank when its bone dry. i have a delorean industries GM style pump kit installed. the electronic sender must not read properly. any ideas there? maybe go back to a stock sender?

[dn010]

Maybe the float arm on your pump is catching on something, it's pretty easy to remove the pump from the tank and see what your gauge reads with the pump out. If the gauge shows empty with the light on, then you know you have something in the tank stopping it from going low or you may need to bend the arm to get it right.

I didn't install DPI's system, but I did upgrade to the same style pump from a Tahoe. I opted to keep the original sending unit system and didn't even attach the float arm to the pump. Even with the original setup (I am using an updated sending unit), I can't really count on it 100% - when I am getting low on fuel sometimes I can go up a hill and the light will come on, then suddenly I have over a 1/4 tank going down the other side (I wish there was more of a delay). I've just made it a habit to stop shortly after seeing the light come on.

Edit: The start of DPI's instructions say the sender is fully programmable, so maybe start there first.