1991 tbi fuel pressure drop

[Edmduncan]

Have trouble keeping the truck running , cranks but won't start unless push peddle half way then catches but dies even when warm if foot comes off gas.
Tested fuel pressure with pressure tester just before fuel filter. Turn ingnition on pump pressures up to about 12psi, then pump stops as normal and pressure guage instantly drops to zero.
Is the pump shot allowing fuel to bleed back not keeping line pressurized or is it the regulator? Figure if it was the regulator though it would bleed off a little slower.
Thoughts? I have a video of the guage under the truck but it's to large because of the 10 seconds or so it takes for the pump to stop.

 

[man-a-fre]

Test your tps for .45-60 volts no throttle, may be a bad tps.

 

[Drunkcanuk]

Hey fellow Canuck.....I'm about 45min north of the E-town.
Anyway....if you have the original fuel pump in there, I had almost the same symptoms and when I was done chucking parts at it and dropped the tank for a new fuel pump, the little rubber hose that attached the pump to the hard line was swiss cheese. Ethanol gas ate it up, new pump had a hose rated for ethanol. NOT saying it's your solution, but could be as simple as that.

 

[PlayingWithTBI]

Turn ingnition on pump pressures up to about 12psi, then pump stops as normal and pressure guage instantly drops to zero.

That's normal. When you turn the KOEO the ECM turns on the fuel pump and, if it doesn't see any DRPs (Distributor Reference Pulses) within 2 seconds, it shuts off the pump, Since there isn't a check valve at the regulator, your pressure bleeds back to tank through the return line.

As @man-a-fre suggested, check your TPS voltage, if it's too high the ECM thinks you're in flooded mode and will shut off the fuel pump.

 

[Edmduncan]

Hey fellow Canuck.....I'm about 45min north of the E-town.
Anyway....if you have the original fuel pump in there, I had almost the same symptoms and when I was done chucking parts at it and dropped the tank for a new fuel pump, the little rubber hose that attached the pump to the hard line was swiss cheese. Ethanol gas ate it up, new pump had a hose rated for ethanol. NOT saying it's your solution, but could be as simple as that.

Hey great to hear from someone local, I replaced my whole fuel sending unit two springs ago. That being said it was a cheaper assembly and not a Delphi or that high end.
I have a new Delphi pump motor on order and regulator so I'm going to chase that rout. I have been driving allot of gravel back roads lately so maybe something also come loose on the pump assembly. I will definitely check the hose on the pump for sure. Thank you.
Where abouts are you, I travel to around Rochester almost every weekend as we have a seasonal in that area.

 

[Edmduncan]

Test your tps for .45-60 volts no throttle, may be a bad tps.

I will check that out for sure, I have replaced it but maybe it catered.

 

[Drunkcanuk]

If you replaced all that a few years ago chances are the rubber hose was changed as well, I wish I had done the pump the year before when I changed the tank due to it splitting and not being able to fill over a 1/2 tank. But got damn good at dropping a tank by myself!!! Lol

I'm out in Westlock. Used to have friends a few decades ago out in Rochester, love the Tawatana valley area.

 

[Schurkey]

Tested fuel pressure with pressure tester just before fuel filter. Turn ingnition on pump pressures up to about 12psi, then pump stops as normal and pressure guage instantly drops to zero.

As said, TBI fuel system does not retain pressure.

What are the chances your fuel filter is plugged? If you're testing before the filter, restriction in the filter wouldn't show up.

Connect a scan tool, look at the rest of the sensors and outputs.