Lets talk FUEL PRESSURE

[Manimal]

I have a 1998 Chevy K1500 5.0. I have replaced the spider with the MPFI spider, cap/rotor(Standard Ign Blue Streak), AC Delco iridium plugs, AC Delco wires, distributor gear...truck has 190k miles. I was getting a P0306 code. Removed plug and it was fouled with build up cleaned and swapped with #2 plug. No more P0306 code, but now P0300! I checked fuel pressure KOEO=50psi...everything I read says thats TOO LOW..So, I replaced the fuel filter, same reading. Went to Autozone and got the Delphi fuel pump($203), istalled and I am getting the same fuel pressure reading...WTF? the truck runs an starts instantly, but still has a noticeable miss. KOEO pressure hits 60psi while priming then drops straight to 52psi. Running=52psi....what am I missing?

 

[Blaine Cornelius]

I would check your pressure gauge. Any other trucks you can hook it up to? I have the same truck.

Mine runs at 56psi.

Then if it checks out your gauge is accurate, I'd start checking fuel lines for kinks/seeps/ballooning etc.


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[Manimal]

Thank You. I will check first thing in the morning

 

[Justin S]

Try a crank relearn

 

[shorepatrol]

Try a crank relearn

Why ?

 

[Justin S]

Sometimes helps with a p0300 unless it's detecting an actual misfire from a specific cylinder

 

[meterman]

U replace the fuel regulator


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[Supercharged111]

U replace the fuel regulator


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It comes with the spider. What brand of spider was used would be my question. A follow up would be this: with real injectors is the engine still that sensitive to fuel pressure? I suspect not. When you rev the engine, what is your fuel pressure? If it's 60 you're fine. It's going to drop with vacuum.

 

[Manimal]

I used the Standard Motor Products spider mpfi conversion.
I have not had a chance to check lines for obstruction or kinks as I was gone yesterday. But I did just go out and this is what I did...
KOEO.....pump primes to 60psi for 2sec then drops to 52psi...start truck pressure rises to 58 instantly and falls just as fast back to 50psi...at IDLE=51/52 psi, rev engine quickly(blip the throttle) pressure goes to 58psi and back down to 50/52 at idle. This is the Delphi fuel pump from Autozone. Oriellys has the precision brand, which I have not had luck with.....SO...Where do I look?
How do I dead head test the pump? Wont the pressure be the same dead head as at the port? It does not bleed off quickly, so a leaky injector is not suspect, and neither is the return. I am confused.

 

[Manimal]

its been approximately 10min and the pressure has gone from 50 to 48. Is that bleeding off too quickly?