The purpose for my post is to gather information regarding the adaptivity of returnless systems on the more modern engines being used in swaps today. I am in the process of a 3500 LX9/4t60 swap and have run into the issue of replacing the fuel rail of my returnless setup with a fuel rail that is compatable with the current fiero system. I have been gleening info from various sources and would like to completely understand what must be done to convert the returnless system into a system such as the stock fiero. Below is a picture taken from Darth Fiero's LS4 build. I have modified it so its operation can be explained better.



A) From fuel tank
B) To fuel rail
C) Fuel Pressure Regulator
D) Return to fuel tank
E) Filtered Fuel
F) T fitting
G) Vacuum

It appears that fuel from the filter goes to the fuel rail via the T fitting (F). The Fuel Pressure Regulator output (C) appears to be connected to the T fitting (F). The Fuel Pressure Regulator input (C) is then connected to the return to the fuel tank (D). If the Vacuum (G) is left unconnected, wouldn't the pressure be a constant PSI? Can someone explain how this is supposed to work?

[This message has been edited by flimbob (edited 03-02-2010).]

i just used 3400 rails, 3400 fpr, and L67 injects. problem solved.

That is obviously just missing the connection to the intake manifold.

Thats the way mine is set up, I put returnless lines on my 3800SC set up.. obviously with the manifold pressure line connected.

[This message has been edited by doublec4 (edited 03-02-2010).]

The manifold connection was the missing piece. For those of us that are contemplating the stock 3500 swap, make sure to get a 00+ 3100 or 3400 FPR as they will be 55 PSI. An adjustable FPR would be needed for anything other than a stock 3500 swap.

i have the stock 02 GA 3400 FPR on my modded 3500. pushing 43.5 psi. good enough for l67 injects and a 88 zr1 fuelpump. think i might be pushing too much fuel haha...

Ben( WOT-TECH ), over at 60degreev6 forum told me that all 3x00 FPRs from 2000 to present are 55 PSI. My 3100 fuel rail from a 01 Malibu had Multec 2 19lb injectors and what I thought was a 55 PSI FPR. Autozone shows different part numbers for a 99 GA FPR and a 02 GA FPR, but has the same part number for a 01 Malibu and a 02 GA. Have you actually measured your fuel pressure? From what I understand, you have a modified engine which would require more fuel. On the other hand, I may have to wait until I can measure my fuel pressure to determine if the FPR is infact putting out 55 PSI.

[This message has been edited by flimbob (edited 03-03-2010).]

55 psi really? thats odd. both of my 2000 era FPRs have always been hovering at 43.5 psi. thats at idle of course. unless the 55 is being measured with an open throttle.

flimbob

Let's revisit your labeling a bit, just for ease of understanding....

A - From fuel tank
B - Pressure Regulated Fuel Feed to Fuel Rail
C - Fuel Pressure Regulator
D - Fuel Return to tank
E - Pressure Bleed through Regulator
F - AN 'Tee' Fitting
G - Vacuum Signal Port on Fuel Pressure Regulator

The FPR output actually goes to the fuel tank. Line C is actually the input to the FPR.
The FPR is controlled by the vacuum signal from the engine, the line is not hooked up in Darth's photo.

Hope this helps in understanding how this setup works.

It sure cleans up the top of the engine.

Any discussion of fuel pressure is meaningless without specifying how it was measured. Was it compared to the atmosphere?

For simplicity, please state the pressure difference across the injectors.

The pressure difference is a standard that anyone can compare.

I would think that the fuel pressure mentioned in this thread is based against atmospheric pressure.

How do you suggest that the delta P be measured on a fuel injector by the average guy?

The easiest way would be to measure gage pressure with the vacuum line disconnected from the regulator. Any average guy can do this.

[This message has been edited by pmbrunelle (edited 03-04-2010).]

That would give the unregulated pump fuel pressure (or max pump pressure), but not delta P across the injector, as the injector discharge point pressure (positive or negative) is unknown.

I'll revise my previous statement (which didn't make sense):

Force the fuel pump ON by shorting the appropriate ALDL pins.

Test gage fuel pressure with engine OFF.

[This message has been edited by pmbrunelle (edited 03-04-2010).]

Most specs just call for a pressure range, engine running, pressure gauge hooked to Schrader valve on fuel rail. Pressure has to be high enough to assure good atomization and spray pattern, high pressure could indicate plugged or nonfunctioning injectors (there would be supporting symptoms), low pressure a bad pump, regulator or injectors.

The post is actually about the "returnless" set-up in Darth Fieros picture, it is not actually returnless, the return is there, it's just not on top of the engine in plain sight.

It's a good setup, I hope my earlier comments helped with understanding of how it works.

Joe

[This message has been edited by olejoedad (edited 03-04-2010).]

quote Originally posted by olejoedad: Most specs just call for a pressure range, engine running, pressure gauge hooked to Schrader valve on fuel rail. Pressure has to be high enough to assure good atomization and spray pattern, high pressure could indicate plugged or nonfunctioning injectors (there would be supporting symptoms), low pressure a bad pump, regulator or injectors. Joe

Sorry, but that is just wrong.

A regulator regulates pressure... and unless you put more than 2 walbro fuel pumps on the feed side, the regulator will have no issues returning the extra fuel back to the tank, engine running or not.

Your right, the high pressure diagnosis is wrong. The regulator would regulate to the proper pressure.

Should have stopped while I was ahead.

Thanks Dark.

anything new on this?