H3T Running out of Fuel with an 1/8th of a Tank Left

[CaseyS]

Can you post the drawing that shows fuse #3 to the fuel pump.

 

[RamRod]

Can you post the drawing that shows fuse #3 to the fuel pump.

Thats the thing, The only thing that tells me that #3 is the fuel pump fuse is under the fuse box lid its listed as such...but nothing else shows it on the diagram and its been making me wonder if it really is the right fuse...

Here is the fuse box layout in the manual:

 

[chaos254]

The wiring diagram shows fuse 29 and 54. There is not one specific to the fuel pump. Have you tested for power to the pump from the fuel pump control module?

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[RamRod]

The wiring diagram shows fuse 29 and 54. There is not one specific to the fuel pump. Have you tested for power to the pump from the fuel pump control module?

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I have an nothing, this is both with the new Fuel Pump Control Modual and the original.

I have read that the new FPCM has to be re-flashed, but when I called the dealership about getting that done the shop foreman called me back after looking into the procedure and said that it is just plug and play...

I have started to open up the wiring loom from the FPCM to the pump and so far it looks like the wires to the pump are very well protected from the factory.
From outside in there if first the slip loom cover, then the fuel pump sending unit wires are wrapped in tape overtop of the fuel pump wires which are wrapped in their own tape

 

[RamRod]

UPDATE: so I opened up the loom as much as I felt comfortable, which was about 3/4 of the harness from the FPCM and the fuel pump in total, basically the only part I didn't check was the section that ran over the frame rail and too many other electrical connections splitting off of it to deal with (and everything looks as it should the whole way).

Using a test light I checked for power coming out of the FPCM to the pump again, nothing at all.

To me that means that the issue is the FPCM or one of the devices that sends a signal to the FPCM.

While I was taping the harness back up and putting sections on the harness into the loom I heard some sort of audible noise turn on out of the blue (I don't think I was touching anything on the truck at all just laying under the truck) and then I was pretty sure I heard the fuel pump kick in.

Put my ear to the tank and sure enough you could hear the pump doing its job!

turned the ignition and the truck fired up!!

So I need to figure out what made that sound, how it interacts with the FPCM and then that should lead me to the answer of WTF is going on!!!!

Thanks for all the help and suggestions so far guys, I am/we are, starting to get this nailed down!!!

 

[RamRod]

For the record I never figured out why the power stopped at the FPCM so I just cut the power line to the fuel pump out of the harness after the TPCM and hooked it up to a switched power source which just runs the pump when ever the ignition is on... now the truck runs and drive like normal...

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[RamRod]

Not sure if anyone knows about this recall, but I am 99.9% sure this is what I am have an issue with!

The bulletin describes my symptoms to a tee!

https://www-odi.nhtsa.dot.gov/acms/cs/jaxrs/download/doc/UCM472842/RCRIT-14V614-0055.pdf

Called GM but they say my VIN is not covered under the recall and now I am in a battle with them to replace it under the recall......


It has been months of work, tinkering, its been to two dealerships & a tonne of head ache trying to figure this one out.... and I am soon to figure out if I was right months ago when I bought a Fuel Pump control module (Fuel pump flow module) but was informed by a dealer that the part was plug and play (it's not. It needs to be flashed....)

 

[Flamingtaco]

I know this was back in April, but no one commented on the occurrence...

Fuel pumps pull enough current to warrant a power relay (rather than being transistor driven). The noise you heard, after which the pump started running, was most likely the relay for the pump, and the fact that you are hearing it is a sign that it needs to be replaced. Relays can sing, whine, repeatedly click, etc. when they are on their way out. So can transistors.

When integrated into modules, there could also be an issue of a cracked solder joint at the relay. First thing I always do when I suspect a bad relay in a module is wet the joints, even if they look good. Cold welds can be difficult to spot sometimes.

I don't know anything about the hummer's fuel pump. Some vehicles have multiple speed pumps, basically two sets of windings inside the motor. Do not drive both windings simultaneously if it does, the motor will burn out.

One the plus side of things, you've got a harder to steal than normal hummer if the switch is well hidden.

 

[4speedfunk]

so I just cut the power line to the fuel pump out of the harness after the TPCM and hooked it up to a switched power source which just runs the pump when ever the ignition is on... now the truck runs and drives like normal

Bing bing bing! GM has a history of making the simplest task, incredibly complicated and unreliable. BTW, Flaming Taco has a good point. I don't know much about the H3 fuel system but my 99 Burb (5.7 Vortec) has pump relay issues. I've had to bypass it with a paper clip, and now I carry a spare relay at all times. Can't go wrong with a good ole manual switch.

 

[RamRod]

I know this was back in April, but no one commented on the occurrence...

Fuel pumps pull enough current to warrant a power relay (rather than being transistor driven). The noise you heard, after which the pump started running, was most likely the relay for the pump, and the fact that you are hearing it is a sign that it needs to be replaced. Relays can sing, whine, repeatedly click, etc. when they are on their way out. So can transistors.

When integrated into modules, there could also be an issue of a cracked solder joint at the relay. First thing I always do when I suspect a bad relay in a module is wet the joints, even if they look good. Cold welds can be difficult to spot sometimes.

I don't know anything about the hummer's fuel pump. Some vehicles have multiple speed pumps, basically two sets of windings inside the motor. Do not drive both windings simultaneously if it does, the motor will burn out.

One the plus side of things, you've got a harder to steal than normal hummer if the switch is well hidden.

Great info, thanks for posting as I am sure this is all going to help someone down the road... I really should get the title changed so i would come up better in a search

so far the pump has never pulled more than 10 amps which surprised me in a way

 

[amrg]

I know this is un related but by any chance is the "fuel rail pressure sensor" located just by the back driverside of the engine wired back to this module?
I am only asking coz you said you went throught the wiring loom so perhaps you have an idea!
I currently have a P0191 code and it was for that sensor. I am inable to find its corresponding pin at the pcm and I am hoping you may have an idea. I played with the wiring and a P069E came up. Now the P0191 (Fuel rail pressure sensor performance) code is gone and I have a P0192 (fuel rail pressure sensor voltage low) DTC and I dont know where to look next.

 

[RamRod]

I am not 100% familiar with that system but I believe the pressure sensor sits on top of the fuel tank and looks like this:

https://www.rockauto.com/en/catalog...,1443938,fuel+&+air,fuel+pressure+sensor,6376


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[amrg]

Thats the fuel tank pressure sensor. There is another one on the fuel lines just before it plugs into the fuel rail at the engine.
I cant find a wiring diagram for it!

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[RamRod]

Thats the fuel tank pressure sensor. There is another one on the fuel lines just before it plugs into the fuel rail at the engine.
I cant find a wiring diagram for it!

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Oh right! well I will see what I can drum up for ya in the info I collected!