Fuel Pressure drops under boost.....NEED HELP!

[Don W.]

Re: Fuel Pressure drops under boost.....NEED HELP!

Disconnected vac line to WG actuator......tested it very slowly and it hit a max of 15psi on the Autometer. Seems like something is still holding it back......I doubt it would max out at 15psi on it's own?

Could. Question is, how did it run and what was your fuel pressure?

 

[GAShan]

Re: Fuel Pressure drops under boost.....NEED HELP!

MIne had the same problem and it turned ou the fuel hose between the pump and the sender assembly had become porous (damn ethanol). You could cut it with a fingernail. Some of the fuel wasn't making it to the rail, it was just going back into the tank. Fixed at last FAST wrench session with Goodyear green stripe ethanol/diesel safe fuel line. Just an idea.

 

[Quickstop [UK]]

Re: Fuel Pressure drops under boost.....NEED HELP!

Borrow a radiator pressure tester. Or buy a cheap one at Harbor Freight. With the engine idling, and your fuel pressure gauge connected, connect the radiator tester to the AFPR. Pump it up, and watch the fuel pressure. You should get appx 1 pound of increase in fuel pressure for each psi of diaphragm pressure.You'll know in less than 5 seconds if it's the fuel pump, or AFPR. I suspect it's not fuel pressure related at all..

The 8psi threshold is "base boost". If the ECM doesn't PWM the boost solenoid, the waste-gate receives full pressure, and regulates boost to 8 psi. I suspect you have a boost control problem, not a fuel delivery problem limiting you to 8psi.

^^Not really true^^.

It depends on volume required at the FPR pressure. If there is a restriction, the pump may produce up to appx 60-70psi. There will be pressure drop across the restriction. As engine usage increases, when the pressure drop matches or exceeds the FPR setting, then the pressure at the FPR will also fall.

The fuel pump will work "just as hard" with no restriction as it will with the restriction. It takes the same amount of energy to move 10 gallons of fuel at 10 psi as it does to move 1 gallon of fuel at 100psi.(More or less. There's some efficiency loss). But high pressure, or restricted output, causes the pump to run faster. This wears out the brushes and commutators. Not the high pressure itself.

For posterity.