Where does this orange fuel relay wire go??

[missouritig]

Hello,

2000 k3500 rclb 5.7 vortec 4x4

Previously truck had weak power, I had a good deal on the Standard injector spider setup and also bought some new intake gaskets.

I removed the old spider and installed the new one, also replaced the upper gasket and throttle body gasket. To be honest it wasnt that difficult of a job...just time consuming.

Ran the truck around and found it had noticeably more power..but I am still backfiring/pinging/detonating quite a but under full load. This happens when I pull out onto a country road and give it some gas get up to speed fast. Its almost popcorn sounding in frequency.

There are no engine codes. Oil pressure, coolant temp all seem to function as expected. I am having really bad fuel air mix ratios, detonation and pinging under load.

Investigated the fuel pump and traced the harness from the pump to the cab and there is this orange plug and I dont know where it goes. Do I hook it up to the ECM hot 12v bolt? I recall messing with it once a ways back and it used to spark when touching it with 12v...now nothing happens. My theory is this should have been hooked to 12v power and now i have a dead fuel pump.

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The manual said it is related to the fuel/oil pressure switch but i dont understand what a fuel pressure switch is. I know there is an oil pressure switch behind the engine but it cant be that? Rockauto has no such switch so it must be ECM related

 

[Schurkey]

There's no "fuel/oil pressure switch". There is an oil pressure switch that turns on the fuel pump when the oil pressure is high enough to close the contacts.

The service manual should show where that wire goes.

What is your fuel pressure when the engine knocks?

Connect a scan tool, verify EVERY sensor, and computer output. Investigate short- and long-term fuel trims, and make sure the timing retards when the knock sensor activates.

 

[missouritig]

Correction, going to oil pressure switch

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[missouritig]

So the wire im fairly sure is from the loom that comes from the fuel pump and the guide makes it seem connected to the oil switch....but the orange wire going to the ignition is throwing me off because I would expect the fuel wire to go to some sort of ECM solenoid or fuse

 

[east302]

Are you sure that’s a stock wire?

The GM diagram for the fuel pump is below, maybe it will help.

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[Vikingdude]

I found the same one on my truck wrapped in electrical tape and stuffed inside the loom. I assumed it was something aftermarket.

 

[Schurkey]

How does the fuel pump run at all with Circuit 440 not being supplied with power? Did someone bypass the stock wiring?

Does one of those power studs at the fusebox go dead when ECM-B minifuse is pulled? If so, that's where that ring terminal goes.

 

[missouritig]

I found the same one on my truck wrapped in electrical tape and stuffed inside the loom. I assumed it was something aftermarket.

This might be it! Maybe for dual transfer tanks or something?

It still doesnt make sense to me on the wiring diagram though...wouldnt a spare wire for vehicle platform options be obvious if it was factory?

 

[missouritig]

How does the fuel pump run at all with Circuit 440 not being supplied with power? Did someone bypass the stock wiring?

Does one of those power studs at the fusebox go dead when ECM-B minifuse is pulled? If so, that's where that ring terminal goes.

Im going to do some fuel pump testing and see.

 

[grampadirt]

Also note,those two studs(a&b)are controlled by the two green 30amp fuses and are hot at all times.They are part of the supply feed from the battery to the fuse block.