Fuel pressure for 36lb injectors

[Amsterdamned96]

I haven’t bothered to look into the details of your build but i have a similar mpfi setup on a big-block and if you’re saying you do not have an aftermarket/inline pump then I’d do a fuel-pressure check or simply check with the manufacturer specs (45psi or more, I imagine) and do a pressure-test by the fuel rail.

 

[L31MaxExpress]

Pressure needs to be checked at the rpm/load the problem exists at. Can carry good pressure at idle or under load at lower rpm but have the pressure fall off at higher rpm. That being said the Delphi replacement pump powered by a Racetronix hotwire in my Express has gone far beyond what I expected it to be able to support. Supports my 383 on E85.

 

[GMCBurb99]

Pressure needs to be checked at the rpm/load the problem exists at. Can carry good pressure at idle or under load at lower rpm but have the pressure fall off at higher rpm. That being said the Delphi replacement pump powered by a Racetronix hotwire in my Express has gone far beyond what I expected it to be able to support. Supports my 383 on E85.

That’s exactly what’s going on. Pressure is fine at idle, when you throttle it up in park, and under load under low rpm, but at higher rpm under load is when it starts falling on its face, usually around 4000rpm and above. I found a unit from Racetronix that’s 340LPH and is a direct drop in and isn’t much more expensive than the Delphi and is e85 compatible. Ordering today so I’ll know in a few days if that solves the issue, but I needed a new pump anyways.

 

[Supercharged111]

So you're shotgunning a pump at it without verifying if you actually need one? I'd be wise to log my fuel pressure when I get back to a lower elevation, but I don't recall my tune indicating a need for a larger pump in my 1500. Right now it still has a stock pump. The dually outran the stock replacement pump that was in it. The 1500 is making about 360 crank here, so north of 400 at a lower elevation. To me a fuel pump is one of those "if it ain't broke don't fix it" type of thing. What are your AFRs doing at 4000?

 

[GMCBurb99]

So you're shotgunning a pump at it without verifying if you actually need one? I'd be wise to log my fuel pressure when I get back to a lower elevation, but I don't recall my tune indicating a need for a larger pump in my 1500. Right now it still has a stock pump. The dually outran the stock replacement pump that was in it. The 1500 is making about 360 crank here, so north of 400 at a lower elevation. To me a fuel pump is one of those "if it ain't broke don't fix it" type of thing. What are your AFRs doing at 4000?

Dude it’s the pump period!! I checked it under load at wot it starts dropping off around 3900 and keeps dropping off from there on.

 

[Supercharged111]

Dude it’s the pump period!! I checked it under load at wot it starts dropping off around 3900 and keeps dropping off from there on.

And where, pray tell, did you say that pressure drops under load in this thread?

 

[GMCBurb99]

And where, pray tell, did you say that pressure drops under load in this thread?

 

[GMCBurb99]

Supercharged111you might want to read the whole thread before you make a comment

 

[Supercharged111]

Supercharged111you might want to read the whole thread before you make a comment

And you might want to read what you posted in this entire thread, because I did. Words mean things, and nowhere did you say pressure was falling off. You said the truck was falling on its face which could be caused by any number of things.

 

[L31MaxExpress]

And you might want to read what you posted in this entire thread, because I did. Words mean things, and nowhere did you say pressure was falling off. You said the truck was falling on its face which could be caused by any number of things.

I will add, he stated in a response to my post that he had NOT checked the pressure at WOT.

The regulator on my AUS was set at 58ish PSI. I say 58ish because I did not spend $300 on a highly accurate gauge when 1-2 psi variance is not the end of the world. I only check the pressure at WOT when the system will not respond to adding fuel in the tune.