Fuel Pump continuously running after swap. Help!

Ok to make a long story short I just got my 5.3 swap into my 92 obs running. The only problem is that I cant figure out why the fuel pump stays on all the time. I didnt modify the stock fuel pump wiring besides splicing in the new walbro pump plug and running the fuel pump wire to the oem fuel pump relay(green wire with white stripe). And the wire from the new ecu is working correctly. It sends 12v for 2 sec to prime before startup, i checked. But even so, the fuel pump continues to run even with the key off. It will also continue to run with the fuel pump relay disconnected...wtf? Only way to kill it is to pull the fuel pump fuse. And another weird thing is that sometimes it will work properly out of the blue. After the first 2 sec. The fuel pump will stop and will only continue when i crankthe engine. Any idea what is causing this? The grey fuel pump wire ties into a bunch of other stuff and the diagram doesnt make much sense

i had this issue and another member was also which i replied to a few weeks ago. did you try searching before posting? idk who did your harness but you will need to do some tracing and testing and get the schematics for your truck.

http://www.ls1truck.com/forums/showt...580#post518580

The only 2 wires that should have been connected to make the new pump run is the grey wire(+12 volts, relay actuated) and the ground wire. The New PCM controls the original relay with the green white wire once it is undone from the old PCM and wired to the new PCM. The grey wire is from the relay and goes to power the fuel pump.

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Originally Posted by Mickeymotormount

The only 2 wires that should have been connected to make the new pump run is the grey wire(+12 volts, relay actuated) and the ground wire. The New PCM controls the original relay with the green white wire once it is undone from the old PCM and wired to the new PCM. The grey wire is from the relay and goes to power the fuel pump.

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Yes. I hooked it up that way. The problem is that the grey wire is getting constant power even with the relay discojnected. But its weird because i didnt modify that wire at all

And yes i searched for a bit but came up with nothing. Searched google though not this site

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Originally Posted by kewljay223

i had this issue and another member was also which i replied to a few weeks ago. did you try searching before posting? idk who did your harness but you will need to do some tracing and testing and get the schematics for your truck.

http://www.ls1truck.com/forums/showt...580#post518580

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Just visited this post. Funny thing is that i just installed a new oil pressure switch with the swap because my old one was starting to go bad(fluctuating reading). Maybe I got a bad one. Would it still be making the fuel pump run even with the relay disconnected?

ok well again, you will have to get a meter out and do some testing. since you have the 2 second power from the pcm and its running without the relay, then that leaves everything on the output side of the relay including the pressure switch which is actually in parallel... do you know how to read a wiring diagram? did you integrate the harness yourself or did you buy a premade one? what "plug" did you splice in??? (never heard of that)... is it the hotwire kit or something?? is the walbro external or internal? does the pump run ANYTIME that the battery is hooked up or only after you turn the key and shut it off or???

as you can see there are a lot of factors here that you havnt mentioned that are needed to help diagnose this....

in that link, i explained exactly how the fuel pum circuit works so im not going to type it again. grab the diagram for your truck and follow the path from the battery source throuh the relays, switches and compare to what you did to it.

ill give you a hint on how to narrow it down. haha there are 3 connectors you can disconnect (maybe 4 now that you "spliced" one in...). get the pump running when its not supposed to. disconnect the connector at the tank thats mounted on the framerail. if it stops, that eliminates a problem from that connector to the pump. then try the new one you added since im guessing its around that area and see if it stops. if so then move to the connector under the brake booster. should be flat and gray IIRC and has 4 wires.... if it stops then try the oil pressure switch connector. if you get all the way to that connector then your switch is either bad or its wired wrong or something is wrong around there.

basically what your looking for is a 12v+ which is always on that is not supposed to be. thats all i can help you do. like i said, your going to have to get that tester out and find the source. good luck

It was the oil pressure switch. Even though it was brand new it was bad. I pulled the plastic case off of the oil pressure sensor and inspected it. I seen how it works and noticed that the screw that tightens the contacts against the spring was loose. This let current flow to the fuel pump even without oil pressure. I tightened it up and, voila! It works now. I appreciate the help very much. It saved me some serious troubleshooting time.

Btw, I know that i don't have a lot of posts here but that doesn't mean that im totally clueless. I'm more of a forum lurker than a poster. I've done a few turns of a wrench :). Gonna button up a few more things on the truck and then i'll post up some victory pics of the truck. Once again, thanks for the tips guys. Much appreciated!

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Originally Posted by old_betsy

It was the oil pressure switch. Even though it was brand new it was bad. I pulled the plastic case off of the oil pressure sensor and inspected it. I seen how it works and noticed that the screw that tightens the contacts against the spring was loose. This let current flow to the fuel pump even without oil pressure. I tightened it up and, voila! It works now. I appreciate the help very much. It saved me some serious troubleshooting time.

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hey man. i was not trying to imply that your clueless. you just didnt give a whole lot of info about what you had tried on your own to figure it out or how you had your rig set up which makes it hard for us to help. a lil more info would be helpful next time before you post, thats all.

other than that, im happy to hear you got it going. I PERSONALLY would like to know how you came to deciding to tear apart the switch. did you check each connector like i mentioned or just start at the switch? and like i said, i had a similar issue and i just swapped the switch out which solved the prob because i know i wired it wrong. but i never tore it apart. lol i would love to see what screw and spring your talking about. post it here or pm with some pics. just for my own curiosity.

anyway, glad you got her going. sorry if i came off ass an ass. been working looooong days this past week. a lil cranky i guess. but im still trying to give back to this forum that made my swap possible

Well I worked the harness on the truck myself. I removed all the things that I didnt need from the stock harness and labeled and kept everything that I did. Used the nbs fuse block for ease of install. Although if I were to do it again I would take a few more hours and just make a standalone harness to clean up the engine bay a bit. I guess I should of gave a little more info about the truck thats my fault. All of my spare time and patience has went in the truck so it makes it easy to get a bit lazy in other areas.(Havent done my laundry in weeks lol). I'll try to post a pic of what I did to the oil pressure sensor. I don't know if every brand sensor's case will pop off but this one did no problem. I figured out the problem by unplugging the plug to the oil pressure sensor and the pump turned off right away. Also noticed if i wiggled the plug on the sensor that the pump would come on and off which was a dead giveaway that it was something wrong inside of the sensor. Pressure read fine on the gauge, but the contacts inside were an issue.

Glad to hear you got it going. Nice to see it was something as simple as the sender instead of trying to chase down gremlins.

My hat's off to you for working your harness yourself. I did mine as well and it is somewhat of an undertaking. But I feel it gave me a better understanding of the entire system.

yup. working on the harness is def the hardest part. but like mikey said, if there is the need for troubleshooting, now you will have a great idea where to start.

it would be great if you got a chance to post the pics. id like to see how it works inside.