5.3 fuel pressure issues

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5.3 fuel pressure issues

Postby jbabb4057 » Tue Apr 18, 2017 5:43 pm

I finally got a DBW pedal to work, I haven't mounted it yet but thats no big deal. I wonder if you can help with my new problem though. I got the motor in and running. It is a 2005 5.3L with flex fuel injectors. It will start up and idle like a champ as long as you want it to. If you touch the throttle petal though, it will rev slightly then fall on its face. You can smell it running very rich. I first thought the problem was the 02 sensors were too close to the end of the open headers (I'm running the Racing Innovation shorties). I put 18" of flex pipe on the end of the collectors. Still have the same problem. I hooked up the fuel pressure gauge today. When you turn the key on, it goes to 70psi, which I think is way too high, then bleeds off when the pump shuts off. It also holds the 70psi while its running. I have a Walbro 255 in my tank going through stock fuel lines to the stock Sonoma fuel filter then to a Corvette style filter/regulator. I am wondering now if I have a leaking injector since the pressure leaks down so fast. But why is the psi running at 70? Any ideas are very much appreciated.
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Re: 5.3 fuel pressure issues

Postby Rickracer » Wed Apr 19, 2017 5:30 am

Sounds by your description like you have built a returnless system? I'n not positive what the pressure spec is for the flex fuel system, but I'm betting 70 psi is too high. Need more details about the "Corvette style filter/regulator"... I am NOT a fan of single line systems, even on carbureted motors. There are many reasons to run a return style system, and a similar number NOT to run returnless.
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Re: 5.3 fuel pressure issues

Postby jbabb4057 » Wed Apr 19, 2017 6:37 am

Anyone got any ideas? I'm leaning toward a bad FPR for the high fuel psi but I still don't understand why I can't rev the motor at all. The motor came with flex fuel injectors (12580426) from the factory. When texas speed tuned my ECM I also had it on the list of things to do was to make sure these injectors were used. This is my first injected motor and I'm stumped. Any help would be greatly appreciated.
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Re: 5.3 fuel pressure issues

Postby jbabb4057 » Wed Apr 19, 2017 6:40 am

Yes, I am running a fuel rail that does not have a return on it. To compensate for that I have a "vette style" fuel filter/regulator on it. From what I have read it was supposed to "regulate" the psi to 58. Would having too much fuel pressure cause a motor to run rich though? To the point of not taking throttle?
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Re: 5.3 fuel pressure issues

Postby Rickracer » Wed Apr 19, 2017 2:35 pm

Very well could, yes.... :? :thumbsdown:
If it were me, I'd be revamping to a return style system.... :thumbup:
Rickracer
ASE Certified Master Automotive Technician (well over 3 decades of experience, :thumbup: )
'93 S10 SB,RC, Comp XR276 Hydraulic Roller, Vortec head 363, 400 + hp, built 700R4, JW 2800 stall lockup converter, 3.73 posi, disc brake, narrowed 8.8 Exploder rear, LS Camaro front discs, Cal-Trac clone traction bars, Best N/A passes to date: 7.76 in the 1/8th, 12.24@109.27 mph in the 1/4, gonna spray it one of these days... :mrgreen:
76 Chevy Vega Drag Car, TWIN TURBO 355, P/G trans w/ brake and JW 4000 stall vert, 4 link back half, narrowed 9", 3.50 gears, 29.5x10.5W ET Drags. Best time9.669 @ 139.79, Latest video: https://www.youtube.com/watch?v=S59riYn ... ata_player
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Re: 5.3 fuel pressure issues

Postby AWD V8 » Wed Apr 19, 2017 2:49 pm

The "return" to the regulator/filter cannot be lower pressure than what the pump puts out dead headed, which is technically what you have done. You have plumbed the return line into the supply line.

These pumps put out 70-90 psi when dead headed. On a return style system the regulator on the engine bleeds off pressure to the tank so that the rail/injector pressure is around 55-60 psi. That is what the PCM is expecting.

I'm not sure how the corvette filter/regulator drops the pressure, but you obviously have maximum pump pressure at the filter, the system cannot drop the system pressure lower than the pump pressure because it cannot bleed it off to the tank.

If you where to check the fuel trims they would be through the roof because the PCM cannot dial back the "on time" of the injectors enough to compensate for that drastic over pressure situation. This is why it's dying when you hit the gas. When idling it normally is running lean, in your case "lean" is way too rich. Once you hit the gas the PCM is programmed to richen the mixture. You are already way too rich, hit the gas and it pushes it way over the top. I'll bet if you pulled the plugs they would be black.

Injectors are rates in lbs per hour at a particular fuel pressure. If you up the fuel pressure you up the flow. The PCM controls the mixture, going by the feedback of the oxygen sensors by increasing or reducing the on time of the injectors. I hope you are using oxygen sensors. If you run the engine too long in this condition it can foul the O2 sensors.

Rick is correct, so many reasons to run a return style system. Your truck already has a return line, just plumb the return line to the existing one and use a regular fuel filter. It shouldn't be much of a change plumbing wise and should cost much.
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Re: 5.3 fuel pressure issues

Postby jbabb4057 » Wed Apr 19, 2017 4:00 pm

I am running the vette style filter/regulator because my truck does not have a return on the fuel rail. It only has a fuel input line. The motor is a 2005. I understand what you are saying but I plumbed it this way because this is what I have seen others do before and theirs worked. Today I went and bought a new vette filter/regulator on the off chance that mine was screwed up. It now has around 64-65psi when running. This is better but from what I'm told it should be 58. I am wondering if my tuner programmed my ecm for the right injectors. I had it on my list to program it for flex fuel injectors but maybe that got over looked. Going to a return style fuel rail would invlove me switching out to a different fuel rail, not simply plumbing it up different.
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Re: 5.3 fuel pressure issues

Postby AWD V8 » Wed Apr 19, 2017 5:00 pm

Sorry, I didn't see that the engine had no fuel return.

I don't know if the pressure should be that high even for a non-return system. If it's regulated at the fuel filter then I don't know what the fuel pressure should be before the filter.

Obviously I've not read enough about that system.

EDIT: I've read that the flex fuel engines require 42-48 psi
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Re: 5.3 fuel pressure issues

Postby Rickracer » Thu Apr 20, 2017 7:15 am

Change the fuel rail or change the pump, those are basically the two choices....of the two, I'd change the rail and plumb the new one to a return line. :wink: 8)
Rickracer
ASE Certified Master Automotive Technician (well over 3 decades of experience, :thumbup: )
'93 S10 SB,RC, Comp XR276 Hydraulic Roller, Vortec head 363, 400 + hp, built 700R4, JW 2800 stall lockup converter, 3.73 posi, disc brake, narrowed 8.8 Exploder rear, LS Camaro front discs, Cal-Trac clone traction bars, Best N/A passes to date: 7.76 in the 1/8th, 12.24@109.27 mph in the 1/4, gonna spray it one of these days... :mrgreen:
76 Chevy Vega Drag Car, TWIN TURBO 355, P/G trans w/ brake and JW 4000 stall vert, 4 link back half, narrowed 9", 3.50 gears, 29.5x10.5W ET Drags. Best time9.669 @ 139.79, Latest video: https://www.youtube.com/watch?v=S59riYn ... ata_player
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