The miracle of the fuel pump that runs without a relay

My plan to clean the fuel injectors on my 2008 Silverado LS 4.8L V8 came to an abrupt halt when I was unable to disable the fuel pump relay because it is missing from the spot where it should be located according to the schematic in the owner’s manual. Does anyone have any ideas on this? Would removing the “fuel system control module” (fuse #21) instead of the fuel pump relay work? Thanks!

Evidently they made some revisions to the wiring at some point and either the relay is elsewhere or an electronic module handles the whole deal. Pull the fuse and see if the pump still runs.

Thanks for your reply. I’ll go head and pull the module later today and see if that does the trick.

+1 for @oblivion. My thoughts exactly.

I looked it up and here is what I found. Fuel pump fuse is 21 under the hood.

Thanks for posting the diagrams! My F/B diagram is still a little different and doesn’t have the fuel pump relay or fuse as depicted - even on my own truck!

So I took Oblivion’s advice and pulled the fuel system control module (#21 on my truck’s F/B diagram). I pulled it while the truck was running - because I couldn’t hear the fuel pump otherwise. The truck stalled. Assuming I was on to something, I then hooked up my OTC fuel injector tool to the schrader valve on the fuel injector rail, adjusted the PSI as described in the OTC application manual and then attempted to start the truck. Unfortunately, it did not start.

So, assuming that pulling the FSCM #21 really did disable the fuel pump, I wondered if it might be something else. After looking a little more closely at the OTC manual (I bought the manual after I had already tried and failed at this once), it actually calls for a different adapter than I have that hooks directly to the fuel supply inlet rather than to the schrader valve.

I purchased the OTC tool and schrader valve adapter after seeing a guy demonstrate this cleaning procedure on you tube on a 2008 Silverado 6.0L, which by the way, according to the manual, also calls for a fuel supply inlet adapter. So to make this long story even longer, I’m probably going to seek out a mechanic in person who can at least confirm the proper process for disabling the fuel pump. If pulling the FSCM is the proper way to disable the fuel pump, then I would imagine I’ll have to order the other adapter to hook up the the fuel supply inlet. If it turns out that pulling the FSCM isn’t the way to disable the fuel pump, then I’ll make another attempt at running the cleaner through the schrader valve on the fuel rail. Thanks again for all your assistance.

You did replace the #21 control module before attempting to start the vehicle didn’t you?

Not while the OTC tool was connected to the schrader valve. The instructions state that the fuel pump must be disabled (to allow the vehicle will run off the cleaner). Once that didn’t work, I removed the tool from the rail and reinserted the FSCM. The truck started without a problem. Thanks.