07 nbs 4.8 - sputtered on throttle for a week, now dead

[nickvrebel]

You seem to have skipped the first step to diagnose fuel delivery issues: check the pressure on the fuel rail with a gauge. Does the pump even prime at all when you go key on w/engine off? (should prone for 3-4 seconds)

[j-ten-ner]

...I did find a skinned wire that was shorting today on the left front near the suspension. After I repaired that, I now can crank it and it will run for two seconds and quit. Then it will try to crank as if it's out of gas but never run....

 

 

I am not a mechanic and I hate electrical systems in a car.

But you had some success after you fixed the skinned wire.

I would start from there. Maybe there is more.

 

so long

j-ten-ner

[LAYNLOW]

In response to checking the fuel pressure at the rail, I don't mean to sound like an ass here but why would I check the fuel pressure at the rail when the fuel pump won't run? I already know there's too little pressure at the rail.

[LAYNLOW]

In response to earlier suggestions, I have left the key on for minutes at a time and yes the rail has a schrader valve. Depressing it trickles gas out. The pump is not being told to turn on by the supply module, which I've replaced as well. There are ten wires going to/from the supply module, so I'm not sure how to troubleshoot forward. Two wires are pos and neg to the module, two are pos and neg to the pump, two are for the fuel level sensor, and three go to the fuel pressure sensor in the fuel rack. The remaining wire (I assume) is the "turn on" wire, which should tell the module to power the pump. It registers 0 volts with key off, and it shows 3 volts (if I remember correctly) with the key on. Does anyone know how much voltage that fuel supply module "turn on" wire should be carrying? Much of the accessories in the truck run off 5 volts, so I don't know what that wire should carry. Further, I don't know what turns that wire on. The fuel pressure regulator, which I didn't know existed and don't know where it's located?

[txab]

The FPR is part of the fuel pump assembly You need to get your hands on service manual with schematics so you can diagnose this

[LAYNLOW]

I thought the FPR was mounted on top of the pump pump assy. It plugs up on top of the pump module next to the fuel level and power plug. It appears to work by sensing vacuum in the tank because the regulator (if that's what it is) is no more than a half inch long and just pushes through the top of the fuel pump module.

Did some more checking and found that the incoming power on the fuel supply module is full time hot. All the other wires are dead with key off except the tan w/ black stripe, which is at 2.75 volts. When I turn the key on this wire stays at 2.75 volts but the blue wire and the gray wire show 12 volts. The rest of the wires are accounted for (they run directly to the fuel pump module for fuel level and power) so the "turn on" signal is being sent to the fuel supply module, the best I can tell. Yet the module still isn't sending

power to the pump. From what I've seen, everything is working properly except that the fuel supply module isn't sending power to the pump. But that part is new. Actually I shouldn't have replaced it because the old one was behaving the same way. Both are getting good power and ground and both are getting the "turn on" signal but neither will turn the pump on. I don't believe both fuel supply modules to be bad. I'm baffled.

[txab]

From the manual:

 

The fuel pressure regulator, located in the modular fuel pump and sender assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.

 

 

Fuel System Overview

 

The Fuel System is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

An electric turbine style fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

[CapitalTruck]

As an aside, is this still covered by the 5yr/100k warranty by any chance?

[LAYNLOW]

Not under warranty any longer but I called for a rollback and sent it to the dealer today because after a long conversation with the service manager, I learned that, since I changed the fuel supply module, the LAN module will need to be re-programmed.

If it turns out to be something additional to that, I'll certainly post the results of the diagnostic.

Thanks for all the info and suggestions. I really appreciate it.

[LAYNLOW]

It turns out that if you replace the fuel supply module, you have to reprogram the computer. $161, including tax and towing. I'm very pleased. I'm more pleased to know that it wasn't something I missed.

Thanks to everyone for their suggestions/advice.

[Surfer_Nick]

Great to hear you're all fixed and back up n' runnin!

[ozzman118]

I have an 07 GMC Sierra with the 4.8L. Have had the code for small leak in evap emissions system on before, then it went to P0449.Have run it quite awhile with this code on. Now having truck shut off while running down road at steady speed. Showing code P069E. Can running with first code be causing the second?