× Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

Fuel Pump Constant on?

  • randall.sick
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
07 Aug 2019 14:36 #32581 by randall.sick
Fuel Pump Constant on? was created by randall.sick
SO I have a 98 5.7 Tahoe LT. I just rebuilt a wiring harness from a 99 Tahoe LT and have made sure to follow the wiring diagrams to the T.

I installed the new/rebuilt harness and started the Tahoe with no problems brought it up to temp, then shut it off. Tried to start it the next day and the battery was dead. Grabbed my jumper pack, hooked it to the battery, and the fuel pump started up, no key in the ignition. Pull the fuse and it stops, put it back in and pull the relay, it stays running.

I don't recall hearing the fuel pump running when I hooked the battery up and started it the first time. I have since, pulled the harness off, rechecked all the lines from the old plugs swapped over to the new harness (Oil pressure was an issue, it has 3 wires on the 98 vs 1 on the 99 harness). I verified all pins had the correct color wires to the ecm plugs and were in the right locations. I even looked over the power distribution diagrams to see if i missed something.

Anyone have any idea what could have happened? I really would hate to have to buy a $2500 harness from an aftermarket place since I have spent over a month working meticulously on this one.

My rides, 1998 Chevy Tahoe 5.7l
1999 Chevy S10 2.2l

Please Log in or Create an account to join the conversation.

  • Tyler
  • Tyler's Avatar
  • Offline
  • Moderator
  • Moderator
  • Letting the magic smoke out since 2011
More
07 Aug 2019 14:51 #32583 by Tyler
Replied by Tyler on topic Fuel Pump Constant on?
Interesting. :cheer: I grabbed the BBB diagram for reference:



Because the pump continues to run without the relay, I think your focus is on the oil pressure switch as an unintentional source of B+. I think your next move is to disconnect it and see if the pump operates normally (if you haven't already). If it does, something is wrong with the switch wiring OR the switch itself. If it doesn't, your next move is voltage checks at the tank.
Attachments:

Please Log in or Create an account to join the conversation.

  • randall.sick
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
07 Aug 2019 15:00 - 07 Aug 2019 15:04 #32584 by randall.sick
Replied by randall.sick on topic Fuel Pump Constant on?
I have the mitchell diagrams, which give me similar schematics, only they cover the whole engine. I am going to reconnect the harness, minus the O.P.S. and see what happens. It won't be today, but I will post what I find. Thanks for the insight, I never thought about the plug itself causing a positive voltage flow.

I also don't see the tan wire that goes from the O.P.S. to the instrument panel to show oil pressure as it runs. Is this a 99 schematic?

My rides, 1998 Chevy Tahoe 5.7l
1999 Chevy S10 2.2l
Last edit: 07 Aug 2019 15:04 by randall.sick.

Please Log in or Create an account to join the conversation.

More
07 Aug 2019 18:13 #32588 by tim.smith1
Replied by tim.smith1 on topic Fuel Pump Constant on?
here is alldata full diagram
Attachments:

Please Log in or Create an account to join the conversation.

  • randall.sick
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
08 Aug 2019 22:07 #32648 by randall.sick
Replied by randall.sick on topic Fuel Pump Constant on?
Thanks for the other diagram. That is the exact one Mitchell's shows.

So I got the harness back on and hooked the battery up, and guess what, the fuel pump came back on without a key on. So I disconnected the OPS plug and it shut off. Started the Tahoe and low an behold, it started without a miss. The oil pressure gauge is reading slap off the dash, but there was life. I shut it off and crawled underneath to try to hear the whinnying of the fuel pump over the cicada in the tree in my backyard, and no noise or vibration from the fuel tank.

I read somewhere that if the OPS fails, then it produces direct power to the fuel pump. So rock auto is about to get more money from me to test that theory!

Update to follow.

My rides, 1998 Chevy Tahoe 5.7l
1999 Chevy S10 2.2l

Please Log in or Create an account to join the conversation.

  • Tyler
  • Tyler's Avatar
  • Offline
  • Moderator
  • Moderator
  • Letting the magic smoke out since 2011
More
09 Aug 2019 21:15 #32688 by Tyler
Replied by Tyler on topic Fuel Pump Constant on?
Nice. B)

I see that RA only carries one three wire switch? Disappointing. Was hoping to see they had an ACDelco three wire in stock...

Please Log in or Create an account to join the conversation.

  • randall.sick
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
09 Aug 2019 23:31 #32694 by randall.sick
Replied by randall.sick on topic Fuel Pump Constant on?
yeah, I prefer the delco or delphi parts as well, but in this case it's just a test. If it works, then I will get one from GM when/if the aftermarket one conks out on me, but at least I can drive it now!

My rides, 1998 Chevy Tahoe 5.7l
1999 Chevy S10 2.2l

Please Log in or Create an account to join the conversation.

  • randall.sick
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
19 Aug 2019 23:31 #32984 by randall.sick
Replied by randall.sick on topic Fuel Pump Constant on?
So I got the new OPS from rock auto only to find out I didn't have a deep enough socket for it. So Oreilly's got me for 12 bucks anyway.

I removed to old sensor, pushed it onto the plug and the fuel pump came on, no key in the ignition, plugged the new one and nothing. so i went ahead and installed it, fired up the beast, and now I have a signal in the dash and a fuel pump that shuts off when the truck is turned off!


So, bad oil pressure sensor in the 98 1500 K body 5.7l will in fact keep the fuel pump running!

My rides, 1998 Chevy Tahoe 5.7l
1999 Chevy S10 2.2l

Please Log in or Create an account to join the conversation.

  • Tyler
  • Tyler's Avatar
  • Offline
  • Moderator
  • Moderator
  • Letting the magic smoke out since 2011
More
20 Aug 2019 09:11 #32992 by Tyler
Replied by Tyler on topic Fuel Pump Constant on?
Nice. B) Glad to hear it's back to working correctly!

Please Log in or Create an account to join the conversation.

  • Not Allowed: to create new topic.
  • Not Allowed: to reply.
  • Not Allowed: to add attachements.
  • Not Allowed: to edit your message.
Time to create page: 0.687 seconds