1998 k2500 suburban fuel pressure drops

[Coothethird]

Hello!
1998 k2500 suburban, 7.4 engine.


I am having a fuel pressure drop when accelerating for more than a few seconds at WOT.

At idle the pressure is around 55 psi, moves up to near 60 psi during tip in or slight throttle. If I floor it to accelerate, after just a few seconds the pressure drops below 40 psi.

The vehicle sat for a long time. The fuel pump completely died. I cleaned the tank, new Delphi complete pump/bucket/sender. New fuel filter.

Is it possible the pressure regulator, or some other component is letting it drop? I bypassed the relay and the pressure moves and holds at 60 psi, with engine off. So I thought the regulator seemed fine.

Or is the pump just not keeping up with demand? I haven't experienced any issues with new Delphi units before, but there is a first time for everything.

 

[JOHNGAAA1]

The 7.4l have a notorious problem of the fuel regulators going bad.

 

[Komet]

I'd probably pop a fresh regulator in and see what happens.

 

[Schurkey]

Fuel pump getting proper voltage/amperage?

Strikes me as an inability to supply high-volume at proper pressure. The pump is weak.

 

[Coothethird]

Fuel pump getting proper voltage/amperage?

Strikes me as an inability to supply high-volume at proper pressure. The pump is weak.

The voltage is right at battery voltage at the pump. I didn't do a current test.

It looks like the pump is weak. Odd for a new Delphi.

 

[Coothethird]

I'd probably pop a fresh regulator in and see what happens.

I think I will re-seal the upper intake anyway. So I'll go ahead and pop a new one in and test.

 

[Supercharged111]

Is it a hard hot restarting pig? These engine are notorious for the regulators sucking as mentioned in addition to the injectors leaking which require upper intake removal to access.

 

[Schurkey]

The voltage is right at battery voltage at the pump.

That's BETTER than I'd expect. GM vehicles often have inherent voltage drop at the fuel pump due to undersized wiring.

Is there voltage on the ground wire?

In both cases, the pump must be running.

I didn't do a current test.

Ideally, you'd verify current with a low-amperage probe and an oscilloscope. That way you can check the amperage draw of each individual bar of the fuel pump armature, and calculate pump RPM.

But an average ampere reading is better than nothing. I just did this two days ago on my '93 Lumina, by connecting an ammeter across the terminals that the fuel pump relay plugs into.

It looks like the pump is weak. Odd for a new Delphi.

Anything can happen, but verify the wire harness (supply and ground) first.

 

[Coothethird]

OK. I replaced the fuel pump (complete assembly) under warranty.

Now it holds pressure under WOT.

It is, however dropping pressure after a few mins. So it is time for new injectors and regulator. I have some bosch replacements for a previous project, so I'll finally put them to use. I have a question about intake manifold gaskets, but will start a new thread to stay on point.

Thanks for all the replies!