What is the pressure produced by the in tank fuel pump supposed to be on a 88 E250 with 5.0L V8......

I've heard 8-10 PSI. Is this correct?

I'm having the issue of low fuel pressure at the rail with key on engine off, or key on engine running, I'm only seeing about ~22PSI with no change as I remove the vacuum hookup from the fuel pressure regulator... The intake manifold vacuum is normal, and the fuel pressure regulator works properly.

I've dropped the tank and attached a fuel pressure gauge directly to the output of the in tank pump, but I've got no pressure.... 0 PSI, although the pump does run and pumps fuel out....

Any info?

 

I've had the issue of hard starts and stalling shortly after startup unless I keep the throttle slightly open during the first minute or two of running....
Also pinging under load while in open loop operation (IE no oxygen sensor controlled fuel trim at play) which to me indicated a lean condition.....

All ignition components were tested and in good shape, so I first replaced the in line fuel filter which is mounted on the frame rail and is downstream of the high pressure pump.... This didn't effect the abnormally low pressure at the rail that I was seeing (which will of course cause a lean condition, until you hit closed loop and then the ECM lengthens the fuel injector duty cycle so as to compensate...... Although the ECM will only lengthen the pulse by so much, and if that doesn't do it, you'll have pinging from the lean mix even in closed loop)

I grounded the fuel pump circuit test port at the connector under the hood (I think this is called the STO connector?) to aid me in the diagnostic process.
Both pumps run when powered, and the high pressure externally mounted one sounds good, but the in tank one sounds bogged down. I replaced the in tank fuel pump screen which did not improve the situation. (Although, my goodness, you should have SEEN that thing!!! It looked awful!)

Tomorrow I will hot wire the intank pump with the gauge connected to it's output and see if that makes it produce pressure, which would indicate a poor connection or wiring issue. Does anyone know where the fuel pumps ground connection is located??? It's not right next to the pump..... The wire to ground goes up into the wiring loom and mingles with a bunch of others as it joins another loom.... I haven't been able to find it yet. Been cleaning every ground that I've seen just to make sure though.

Many thanks for the advice!

 

Ok, I checked for proper voltage and a good circuit at the in tank fuel pump assembly connector (as well as the in line, high pressure, frame moutned pump just to make sure) and it is fine.

Yeah, I did it in the 30 degree weather in the dark--- I'm eager to get this van on the road again.

No voltage when key is off, battery voltage when key is on (for a second or two until the ECM tells the relay to stop priming the line--- or stays energized when you have the fuel pump circuit test port grounded).....
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In case anyone is wondering the pinout of the connector for the in tank pump goes like this(rear tank):
From the drivers side to the passenger's side, the wires are:

Black:to Fuel pump ground
Red: Battery positive via fuel pump relay
Orange: Switched battery positive to sending unit-- this voltage is pulsed, not constant
Black: to ground for fuel level sending unit

The harness for the other tank is identical, although I think the orange wire is a different color.
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When daylight comes, I'll be placing the supply line from the high pressure pump into a container of gasoline and seeing if I can get decent pressure at the rail with this setup (with the in tank pump disabled of course), or if the high pressure pump REQUIRES to be fed it's supply under pressure.

I'm thinking that my weak in tank pump is not supplying an adequate flow and that the high pressure pump is trying to 'suck' through the in tank pump in order to run, but that 22PSI is the best it can do under these conditions.

I'll report tomorrow.

 

Allright, the van starts right up and runs great with about 30 PSI at the rail if I just disconnect the supply to the high pressure pump and replace it with a short piece of hose directed into a bottle of gasoline.

I'm thinking that replacing the in tank pump will boost the rail pressure another few PSI and bring things back into proper order.

I realize that this thread has never evolved past a monologue, however I hope that this information will be helpful to somebody someday.

You can indeed run the vehicle by giving the high pressure pump a drink of gasoline in a can...... This finally helped me to diagnose what has been a series of troubles with the running condition of this van, from hard starts, to no starts, to pinging and stumbling and stalling under load.

I changed all the fuel filters and cleaned the fuel injectors to no great effect.

The in tank pumps DO run, and they pump fuel!!! But not enough to keep from causing all these issues.

I guess the main point is that it seems that usually when a fuel pump goes bad, it stops working entirely. But these things can also work halfway, and progressively deteriorate.

Thanks anyway guys!

 

Dustmote it seems you've encountered a problem most members have never seen---very odd and sorry you didn't find more help here. Its good of you to add your new discoveries even if not replies have been added.

Hope you resolve this soon!