Disabling fuel pump on a 5.3

[LS1CamaroSS]

Hey guys, I'm trying to disable the fuel pump on my 2008 Silverado 5.3L so I can clean the injectors through the fuel rail, but I can't seem to turn the pump off. Under VCM controls, there's a fuel pump on/off option, but it's grayed out when connected to the truck regardless of whether it's running or not. Perhaps there's a way it can be done in VCM editor instead? You're probably wondering why I don't just remove the fuse to the fuel pump, well for whatever reason, with the fuel pump fuse as well as the relay both removed, the pump still runs. Someone mentioned how it may be because the oil pressure switch is possibly wired as a backup to keep the pump running, so I unplugged that too and the pump still runs.

[04silverado6.0]

Put in the fuses and relay and try again in the scanner. May have to reset codes or disconnect battery.

[LS1CamaroSS]

Put in the fuses and relay and try again in the scanner. May have to reset codes or disconnect battery.

I did have one code after I disconnected the oil pressure switch, which I cleared after I reconnected it and reinstalled the fuse and relay, but I'll disconnect the battery and see if that does it.

[blindsquirrel]

With FPCM or without (service manual says LMG/LC9 are without, but you know how that goes)?

[blindsquirrel]

FYI GM hasn't used the oil pressure switch as a backup since the TBI dayz, best I can remember. Your truck certainly doesn't have that.

[LS1CamaroSS]

Unfortunately disconnecting the battery resulted in no change

With FPCM or without (service manual says LMG/LC9 are without, but you know how that goes)?

I have an LY5, but it does say FPCM is enabled and the values appear filled out. Thanks for the info about the oil pressure switch, the TBI years were quite some time ago lol

[blindsquirrel]

screenshot.11-09-2024 20.08.36.png

If it has a FPCM it has no fuel pump relay, if it has a fuel pump relay then it has no FPCM.

(hey, did you know, your tune file has your VIN in it? and if you post your file when asking for help, you can get better answers?)

[LS1CamaroSS]

If it has a FPCM it has no fuel pump relay, if it has a fuel pump relay then it has no FPCM.

(hey, did you know, your tune file has your VIN in it? and if you post your file when asking for help, you can get better answers?)

You're right, I should've posted it from the start. I'll put it in this reply

[blindsquirrel]

Running the VIN through TIS does pull up a FPCM calibration. Normally, though not always, if one is 'not equipped' it will throw up an error message instead.

screenshot.11-09-2024 17.11.58.png

[LS1CamaroSS]

Running the VIN through TIS does pull up a FPCM calibration. Normally, though not always, if one is 'not equipped' it will throw up an error message instead.

So if I were to drop the six values under Desired Pressure down to 0 psi, would that essentially prevent the fuel pump from working?

[blindsquirrel]

I posted a wiring diagram. Pull the FSCM fuse #21.

The fuse & relay you pulled was not the fuel pump fuse & fuel pump relay, because your truck does not have a fuel pump fuse or fuel pump relay, if it has a FPCM.

[LS1CamaroSS]

I posted a wiring diagram. Pull the FSCM fuse #21.

The fuse & relay you pulled was not the fuel pump fuse & fuel pump relay, because your truck does not have a fuel pump fuse or fuel pump relay, if it has a FPCM.

Sorry, I'm pretty bad when it comes to comprehending wiring diagrams. I'll give that a try when I go out there tomorrow, I'll let you know how it goes. It's strange how the fuel pump fuse and relay are in there, but aren't being used. That threw me off.

[LS1CamaroSS]

I posted a wiring diagram. Pull the FSCM fuse #21.

You were right, #21 shut off the fuel pump. I appreciate the help!