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2006 GMC Serria 1500 5.3 4x4 single fuel tank. I had the motor out for total rebuild that took about 3 months due to work and part delays. I decided I would PUMP the old E10 fuel out and start off with fresh fuel before even trying to start it. Soooo I disconnected the fuel line from the rail, connected a hose down to plastic tank for disposal. Turned the ignition key to on and got nothing. Checked fuses, fuel pump, ECM & PCM swapped relays, all is good. I jumped the relay out and got the old fuel removed. So, I did not have this before I pulled the engine, what changed. As a part of the rebuild I installed ALL new sensors. I have triple checked all connections and grounds. I spent most of yesterday on the web, but as you know it was all over the place. I signed up with Alldata to see wiring. Looks very straight forward, PCM #9 Grn w/wht stripe is the control signal to the Fuel Pump. I tested it and there is no power. Am I looking at this right????? What tells the PCM to send the control signal. If it's just the key being on, then if I can't get his figured out, could I not just turn this into a Anti Theft by adding a hidden control power switch to the relay???? WELL I'm sure you all have figured out that I know just enough to be really dangerous. TYIA CHEERS
A fuel pump might run for a couple seconds when the key is first turned to run. To run it any longer than that, or at all, the PCM has to see engine movement. Easiest way to do what you want is to pull the relay and jumper the pumps power circuit.
My post states that I pulled the relay and jumped it to remove old fuel. What I am trying to figure out is why I do not have control power to the fuel pump relay when I turn the key on.
There should be a ignition input from ignition switch to the pcm 12 volt feed. Do you even hear the fuel pump run for 2 seconds koeo? Probably not. Do you have pcm pinout diagram?
If you had a problem with the fuel pump relay control side ground circuit you would not have fuel pump operation. Take a test light connected to battery positive and remove relay touch each terminal should light on 2 one is control side ground other fuel pump load side finding ground through fuel pump brushes low resistance
If pcm wasn't getting ignition input signal before was called crank signal then pcm would not ground starter relay. Will your truck crank? Pcm fuel pump 2 second prime koeo? Maybe open fp control wire check 12 volts on control wire at pcm pin 9 dark green /white wire.
Some things to consider is mice love to get under the fuse block in the engine compartment. (I have the same truck) so pull fuse block up and check the wires underneath going to the relay spots.
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