94' GMC Sierra v8 wiring issues

[Jayp33]

Hey my name's Jay. I jus bought a GMC Sierra v8 and ran out of gas yesterday, and today after getting gas in a gas can and putting it in the truck, it won't start and I'm having trouble identifying the wires in the junction box because previous owner has it Mickey mouse and wired complicated.
HELP

 

[dbrannon79]

Welcome @Jayp33 in your photo that blue wire repair is something that someone has done to bypass a fusable link. not sure what it powers, but the relay next to the junction block right side in the pic is your fuel pump relay. the small box to the left is the fuse holder which has a fuse inside that is for your fuel pump. when you turn the key on (assuming your's is a gasoline engine) listen for the fuel pump to turn on and run for 2 seconds. if not, you will need to check the fuel pump fuse as well as all of the fuses in the cab for power with the key in the run position.

if all checks out good. have a friend cycle the key from off to run (not cranking) and see if the fuel pump relay is working. then it will be to crawl under the truck and access the harness connector on the fuel tank. you will need to check for power there.

when you turn the key to the run position the PCM will turn on the fuel pump for 2 seconds to prime the system. you can test for power that way or have someone crank on it while you test for power with a test light

 

[MrMarty51]

Hello 33, welcome to the forum.
That oval shaped box is the fuel pump relay.
I do not remember what the function of each color of wire does but, IIRC, the red should be power feed to the relay.
If You have a multimeter there shoukd be power to that wire.
If You have a probe/test light, you can check to make sure that wire comes live with the ignition switch in the run position.
If it is live with ignition switch in run position, it can be jumped to one of the other wires to cause the fuel pump to run.
Wait until someone replies tgat has the information as to which wire to jump it to so no other systems gets burned out.

 

[MrMarty51]

Hello 33, welcome to the forum.
That oval shaped box is the fuel pump relay.
I do not remember what the function of each color of wire does but, IIRC, the red should be power feed to the relay.
If You have a multimeter there shoukd be power to that wire.
If You have a probe/test light, you can check to make sure that wire comes live with the ignition switch in the run position.
If it is live with ignition switch in run position, it can be jumped to one of the other wires to cause the fuel pump to run.
Wait until someone replies tgat has the information as to which wire to jump it to so no other systems gets burned out.

I had this all tapped out on my phone then got distracted, regardless, tapped the post button, but, @dbrannon79 had already replied, follow His instructions.

 

[Will L.]

On the gas engines- the fuel pump burns up easily when the filter doesn’t get charged often enough. Filter is inside frame under driver door.
Whenever you run the tank dry- it will pull in every small bit if debris in the tank and plug the filter.

As mentioned- after putting in 5 gallons of gas, cycle the key off on off on- like a ton of times, 20 is a good starting point. Then look at the steel fuel line atop the engine, there is a schrader valve where a pressure gauge can attach. Push the tip like you are letting a little air of a tire. This should SPRAY A LITTLE GAS so have a rag in hand to capture it. Once you know you have gas coming out there, put the schrader cap back on & cycle the key 5 more times- then start it.

Plan on a new fuel filter within the week.

If you don’t get fuel spray- replace the filter first and try again. If you have or can get a fuel pressure gauge- that is next to test. Running an in tank pump dry burns them up quickly.

 

[dbrannon79]

if he has a TBI injection there will be no schrader valve. GM didn't start using those until they went to multi-port injection.

 

[Will L.]

if he has a TBI injection there will be no schrader valve. GM didn't start using those until they went to multi-port injection.

Thats why friends are better than memories- friends don’t let us forget things! That way we end up with both!