This is a very strange problem.

[Shaper79]

ok. Iv been dealing with this a while, 5.7 GSI Throttle body. It has the carter fuel cell with Low pump and Highpump. I have made sure pickup tube is clear , deleted anti “syphon valve for testing purposes “fuel line to fuel cell is clear, pulled fuel cell completely disassembled and cleaned out every spec of paint in the fuel cell. Order new pumps from the “mancave mechanic guy on utube “ pulled the pressure regulator on the throttle body and installed a new diaphragm checked stock spring and cleaned and reassembled. I do not know what stock spring psi is on the GSI5.7 marine motor. The truck motor 5.7 is about 9-12 psi fuel pressure from what I have read. Is the marine 5.7 the same? Idk. My fuel water separator is only installed last summer. Should be fine. “Volvo Penta Brand” this were it gets weird. My LP holds a perfect 8 psi of pressure no problems. But the HP at idle is at 28psi and when I reve it up it drops to 20psi then back to the 28psi. The spec for this is supposed to be 30psi and not lose psi under load. So what in the heck is going on here ! What else could it be. I’m checking psi directly off the pump head

 

[alldodge]

Hey muc have any thoughts?

The regulator should keep the pressure at 30 psi +/- at all rpms. The spring in the regulator sets the pressure, and it loosing pressure when rpms go up would lean me to the either the pump or injectors. If your loosing pressure running and just reving in neutral, then this would lean more to injectors, because they are turning on/off faster and may be leaking.tank

A fuel injection motor is more complex, but the the fuel pressure is pretty simple. Pressure builds up and when pressure exceeds regulator setting the spring is compressed far enough to send fuel back to filter or tank/ Once pressure drops to spring pressure it closes off the return.

If injectors do not shut off completely then there is more loss, and engine will run rich. Plugs should look black if this is happening. If pump cannot keep up then plugs will look normal or more white from running lean

 

[Scott Danforth]

Shaper79
is this a continuation of your other thread? https://forums.iboats.com/forum/eng...tbi-fuel-injectors-you-can-feel-the-burt’s-in

fuel pressure is 2 bar on the marine side. different system for the automotive 1 bar system.

pull the vac line off the regulator, you should get full pump pressure. test the fuel pressure this will determine if its a regulator issue or other.

 

[Shaper79]

Alright guys. Got it fixed. You guys were right. Mine does not have the vac line. Its the throttle body 93-95. The vacuum is built in internally. I found on bottom of the pressure regulator bowl. Ther is a tiny set screw to up the spring pressure. So in turn it in about 5 turns. And boom. It’s finally fixed the problem 31psi at idle now and drops to 30 under load. I know 30 is the factory spec. So I’m assuming 31psi is ok. Thank you guys for the lead. Fixed!!!

 

[Lubak572]

Where is the set screw? I don't recall seeing one when i rebuilt mine.

 

[Shaper79]

[No message]

 

[Shaper79]

The set screw is on the bottom of the green bowl. On the pressure regulator. These do not have a vacuum line. Vacuum is internally built in by passages. The base fuel pressure had the be set by the set screw..... this is what I think happened to me. When I first got my boat 4 years ago it ran great. Perfect, but over time I think that set Screw was slowly backing off and lowering my fuel pressure over time and slowly making my boat run like ****. In return I wanna chase this problem in all directions. Changing all sensors and ignition system to track down the poor poor performance. And thinking the paint chips was the main problem in the fuel cell while working to disassemble fuel cell several times to clean out every spec of paint chips. And even buying new pumps. My low pump was actually bad. But in the end I know my intire ignition system and fuel system is new, and I know exactly how it all functions now.