DKS2K

My 97 running 7065 single top mount is dropping fuel pressure when under boost of 12lbs. Before the dyno we upgrade the fuel pump to a Aeromotive stealth 340 pump and put a new GM fuel filter in. Now we are trying to figure out why its dropping fuel pressure when under boost at 12lbs.. Any help would be great.

Pekka_Perkeles

If I read your graphs correctly, that's exactly what happens without boost-referenced fuel system.

stevieturbo

Fuel pressure measured before the injectors should remain static if not boost referenced.

Actual pressure across the injector will change, but that isnt what is being measured.

Causes can be many. Not enough pump, wiring, lines, regulator, filter etc etc

Pekka_Perkeles

Correct, I agree.

My mistake.

stevieturbo

Although a small drop wouldnt be a big deal...a large drop and as fast as that, far from ideal.

That said, the reading is 85psi dropping to 70psi ?

Firstly why is it at 85psi to start with ? Even if these are absolute figures as the units suggest...which would be around 70psi gauge dropping to 55psi....why is it starting high ?

A lot more info is needed here.

DKS2K

Well my c5 is a 97 with the return system running aeromotive 340 fuel pump and gt500 injector 47lbs.

BLOWNBLUEZ06@RKT Performance

Not enough pump for the given circumstances. It's that simple. As mentioned earlier, it could be from a weak pump, defects in wiring or anything causing low voltage to the pump, or that your demand exceeds the limits of the pump, even when it's working properly.

Fuel volume capability of a pump is based largely on its output pressure and you're running far too much pressure on that pump regardless of any other circumstances.

SBCGENII

What is your base fuel pressure? Is your regulator 2-1 or 1-1?

SmoothFRC

Maybe a silly question, but are you running a Hotwire kit?

Your base pressure just seems really high. Pump maybe cannot keep up at that pressure. Might want to lower that. They have an adjustable regulator for the stock 97/8 rail.

DKS2K

Found out the problem. Need to run a big power wire to the pump.

SmoothFRC

Good to hear it was something simple! good luck.

Chicago1

I wish mine was something simple like that lol

DKS2K

Don't ever get a Aeromotive 340 Stealth pump.. The pump get really hot after a few pulls and cause it to go lean. Going from 11.5 to 14-15 af really fast.

stevieturbo

How did you tell the pump was hot when it's submerged in the fuel tank ?

DKS2K

Would go throw some fuel in to cool down the pump and was fine again for a few pulls then would heat up and fuel pressure would drop. Swap the pump out for Walbro 450 and can do 10+ pulls and never drop fuel pressure or go lean.

SBCGENII

Why isn't your pump covered in fuel like Stevie said?

Drewstein

You went from a 340 to a 450 and you're surprised it flows better? Maybe the 100GPH was the difference...


I'm with everyone else, base pressure seems way to high.

silver408z

Are 47lb injectors really big enough? Is he trying to make up for small injectors with more pressure? I know mustang injectors are rated at a lower pressure but 47lb still seems small.

DKS2K

The Stealth 340 pump was running out at only 515whp.. Well I mean at 515whp after a few pull, the pump pressure was dropping.

SBCGENII

Yea because of 85psi fuel pressure. The higher the pressure you demand on a fuel pump the less it flows. If your pressure was 58 you would have been fine.