Incorrect fuel pressure Key on and Engine Running

[Matthew Jeschke]

Dropped the tank again. I'm loosing track of how many times I've taken the tank off at this point. I took all the lines apart. Blew air down them... No obstuctions what so ever. I even took bypass tube off rail and blew air through it in every way conceivable. I took the test port valve out and did the same. I sprayed all the orings with pblaster and put it back together. Pressurized the system and checked for leaks again and again. I also visually inspected all the lines... no kinks or damage anywhere. Same result from test 48PSI, when is supposed to be 58 PSI to 62 PSI. I am pretty sure the harbor freight kit includes the test fitting for checking pump pressure / unregulated pressure. I'm going to buy it tomorrow and see what results I get. That aside, lines, rail and regulator are working as expected.

 

[Matthew Jeschke]

I'm going to see if maybe I have a poor ground that's leading to reduced current to the pump. Pulled this out of the FSM. But cannot find where G102 or G403 are located. Anybody know?

 

[Fless]

This is what the upfitters guide shows, the fuel pump ground on the body mount underneath the driver's door hinge:



Zoomable PDF attached.

Presumably a high number ground (like G403) would be near the rear of the vehicle, but I'm not sure of that. Alldata would likely show them.

 

[Matthew Jeschke]

@Fless thanks!!! I dug through AllData for quite a while but couldn't seem to bring up those two grounds. I internet searched them, but seems you're picture is much better than what I found on the internet. Very helpful.

 

[nonickatall]

This is normal if your hose is lower than the level of your tank. Then there is this effect.

This is how tanks used to be emptied, the hose sucked in petrol, and the hose hung lower than the tank was full.

 

[Matthew Jeschke]

Oh, that makes since. Hurt like heck though getting my arm soaked in fuel.

On another note, Delphi got back with me. They said I need to do a voltage drop test... from relay to pump, and pump to ground. Guess I need to drop the tank... again. Sigh. At least far enough to fit some probes in the lines to the pump.

I tried test on my Corvette. It was within spec. I did notice one thing though. The pressure PEAKS in the test range. It doesn't STAY in the test range. When the pump cycles on it hits within the test range but once it shuts off it drops below. I assume that's proper function. The FSM wasn't too clear about that.

I've attached troubleshooting guides from Delphi.

Test Measurements:

5 AMPS draw at 12.1V for pump

 

[strutaeng]

@Matthew Jeschke My 99 Silverado has started having an issue where it will crank a while and kinda struggles to start.

This morning I finally put a fuel pressure gauge on it and got 54 psi at prime and like 48 psi at 2,000 RPM.

I don't believe I have a fuel delivery problem...

I guess I'm not seeing how you determined that your fuel pump is bad? Did I miss that? You have a return style setup, right?

 

[Matthew Jeschke]

I have a return style setup. My Key On Ignition off pressure is 48PSI. 7 below spec which is 55 to 62 PSI.

I noticed, fiddling with my Corvette that the gauge will PEAK in the 55 to 62 PSI and settle down a bit lower, possibly even touch below that range. I'd venture you're pump is in great shape if you get 54 PSI during that test. Mine falls to 40PSI when engine is rev'd.

I have a new pump from Delphi (warranty replacement). Original pump I'm quite sure was bad regardless of pressure because the line set bled off quickly after engine & pump were shut off. It'd bleed down to like 35 PSI in a matter of minutes. This new one hold pressure in the lines even as much at 15 minutes later non has bled down.

Delphi tech support has me checking circuitry. They said to do voltage drop tests. I'm going to do that now. One across the whole line for starters then break into the positive side then negative side if necessary. Current draw, patching my amp meter in in place of relay was 5AMPS. I think maybe supposed to be 6 AMPS but battery charge was low. Lots of stuff I'm checking... Will update here as I go through whole process. I should have tested the voltage drops when I had the tank dropped. Now I have to drop it again *sigh* all be it only part of the way to access top of pump.

 

[Matthew Jeschke]

There is a connector, C152A (also C152? connector on wiring diagram but not listed in FSM)... I cannot locate it? Anybody know where it is?

 

[Matthew Jeschke]

Not a single electrical fault. Positive side voltage drop 0.6mV negative side voltage drop 115mV tested against all three chassis grounds on driver side.

I opened up the Harbor Freight fuel pressure test kit. Patched in on input side of fuel rail... 58 PSI. It's supposed to be a minimum of 62 PSI. I'm going to see if I can disconnect front of tank and patch in pressure gauge there to see what pressure I get. Maybe there is an obstruction despite I blew out the lines??? Long shot but I'll see.