Weird electrical problem

[jessemthompson]

I have a gen4 5.3 from an 07 suburban in my 72. The other day driving down the road in it and the truck turn off. I hit the key and it started right back up. Further down the road it did it again. This time it would not start again. I could not hea the fuel pump priming, so I assumed I needed to replace my pump. I had a pump at the house, so no big deal. Anyways, I lift the bed to access my tank. I check the power wire with the key switched on and have nothing. So I go to my fuse panel and my fuse is fine. I check my relay and I have constant power. I hit the key and the pcm doesn’t seem to be sending power to the activation wire (green/white stripe). So I disconnect the plug that runs from the fuse panel to the pcm to check the connection and when I replugged it in, the fuel pump primes! So I check my wires to make sure no pins are loose and they all seem fine. So with the key on, anytime you disconnect and reconnect the plug, the pump primes. Also with power on when I take out the pcm power fuse and plug it back in the pump primes. But cycle the key to the truck and the pump doesn’t prime.

[ls1nova71]

Sounds like your ignition power wire that powers up the ECM isn't getting power. Have you checked that wire? Could also be a bad ignition switch if it isn't putting power on that wire.

[lutronjim]

Kinda/sorta sounds like my problem where when the key is is 'crank position' PCM isn't getting power.

[truckdude239]

check your grounds i had same issuse mine was ground problem on back of the cylinder head

[jessemthompson]

Originally Posted by ls1nova71

Sounds like your ignition power wire that powers up the ECM isn't getting power. Have you checked that wire? Could also be a bad ignition switch if it isn't putting power on that wire.

Ignition switch fixed the issue. Back up and rolling.

[jessemthompson]

Originally Posted by truckdude239

check your grounds i had same issuse mine was ground problem on back of the cylinder head

When I did the swap in 15, I made sure I grounded everything very well. This was the first issue I’ve really had since the swap.

[truckdude239]

i drove mine abour 300 miles started having random cut offs broke down like 3 miles from a friends shop not restart cosated into had them check it out turns out i neve rbolted the grounds to back of the head still havent figured out how i made it that long

[AussieinNC]

When you did the upgrade, did you run the PCM electrical feed thru a relay controlled by the ign switch or did you wire the feed directly thru the switch?

The standard ign switch is not designed to handle the current load of the pcm....

[jessemthompson]

Originally Posted by AussieinNC

When you did the upgrade, did you run the PCM electrical feed thru a relay controlled by the ign switch or did you wire the feed directly thru the switch?

The standard ign switch is not designed to handle the current load of the pcm....

I used an aftermarket harness by bp automotive. I don’t believe there is a relay for the power of the pcm. I know I didn’t go directly into the ignition switch. I’d have to go back and look where I tapped in for power. It’s been 5 years ago.

[jessemthompson]

Originally Posted by AussieinNC

When you did the upgrade, did you run the PCM electrical feed thru a relay controlled by the ign switch or did you wire the feed directly thru the switch?

The standard ign switch is not designed to handle the current load of the pcm....

I have looked more into this and I’ll be adding a relay to my system before this weekend is over. I appreciate your input. Ty.

[jessemthompson]

Today I wired up a relay for the ignition switch to the LS harness to prevent burning up another switch. All is working well. Time will tell how it holds up.