Fuel Pressure Regulator Causing Misfire?

[chubbusket]

Read a bunch of threads on the topic but still confused. 1997 K2500 Vortex 5.7L.

Symptoms: hard starts - have to crank for many seconds to minutes if it even starts at all, engine stalls and misfires and dies if running, bogs down under throttle. It is a relatively new issue.

The fuel pump sounded weird and I thought the check valve might have failed so I changed it and that didn't fix it. I have 55-60psi at the fuel port on the intake but it bleeds off to 20-30psi in less than 10 minutes. This isn't normal is it? I think this means that my fuel pressure regulator is leaking and I probably need to replace it and the spider. I want to be sure though since it is expensive.

Any other things to test? My distributor, wires, and plugs were changed less than 3000 miles ago. Any other sensors failing that would randomly cause this?

Thanks for the help.

 

[stutaeng]

Read a bunch of threads on the topic but still confused. 1997 K2500 Vortex 5.7L.

Symptoms: hard starts - have to crank for many seconds to minutes if it even starts at all, engine stalls and misfires and dies if running, bogs down under throttle. It is a relatively new issue.

The fuel pump sounded weird and I thought the check valve might have failed so I changed it and that didn't fix it. I have 55-60psi at the fuel port on the intake but it bleeds off to 20-30psi in less than 10 minutes. This isn't normal is it? I think this means that my fuel pressure regulator is leaking and I probably need to replace it and the spider. I want to be sure though since it is expensive.

Any other things to test? My distributor, wires, and plugs were changed less than 3000 miles ago. Any other sensors failing that would randomly cause this?

Thanks for the help.

Yeah, not normal to have the pressure bleed off like that. Either the FPR and/or injectors are leaking. That's most likely why engine stumbles and dies; it's flooded with fuel.

Install a new mpfi injector ungrade assembly (it comes with a new FPR.)

Why was the fuel pump replaced? You thought the pressure loss was through the check valve on the pump? That seems to be very unlikely, based on my limited experience. Well, at least you have a fuel pressure gauge.

 

[chubbusket]

Thank you for the advice. It makes sense since I could get it to start sometimes by flooring the pedal to clear the flood. It would usually start ok cold since there wasn't fuel in the intake recently. Warm starts involved lots of cranking if it even started at all.

I replaced the fuel pump since I wanted it to be that and the pressures were a bit low 50-53. However, this was probably since it leaked in the FPR end since I didn't deadhead it for the test. I had hoped for a cheaper solution but it looks like I'm going to buy an upgraded spider. I will report back once I get it installed.

 

[stutaeng]

Thank you for the advice. It makes sense since I could get it to start sometimes by flooring the pedal to clear the flood. It would usually start ok cold since there wasn't fuel in the intake recently. Warm starts involved lots of cranking if it even started at all.

I replaced the fuel pump since I wanted it to be that and the pressures were a bit low 50-53. However, this was probably since it leaked in the FPR end since I didn't deadhead it for the test. I had hoped for a cheaper solution but it looks like I'm going to buy an upgraded spider. I will report back once I get it installed.

Ok, gotcha. That's actually what I was going to ask, but forgot. Unfortunately, having the injectors and FPR under the plenum makes testing rather difficult on these engines.

Take a look at this video on fuel pressure/FPR diagnostics. It's kinda long, but excellent:

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Massive leaky injector causing major fuel pressure loss @ minute 17:

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