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Fuel pump and fuel pump relay. -SOLVED

Pecmoney

Pecmoney

Morale Is Up.
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Pinckneyville Illinois
The previous owner had a fuel cell behind the fold down seat in my 91 k5. He ran his own power wire from the fuse panel off of the ignition fuse to the fuel cell. He also took the TBI off and put a new intake and carb on the engine. I am going back to a stock tank and fuel pump and have a few questions. The pump gets a Tan and white wire (power) a pink wire (gauge) and a black wire (ground). I've tested power to the fuel pump relay and its good going in. I also understand that the dark green and white wire should get power from the ECM for two seconds on key turn to on. NOW. My question is does the tan and white wire only receive power when the motor is running, because I've tried to test it with my test light with the key on and its a no go. Also, can I run a factory tank and with factory fuel sending unit and pump with a carb setup on this K5?

Thanks
-Travis
--edit I have a new tank and sending unit and pump coming this week.
 
Tan/white will only have power with the pump running, yes. That 2 second pump prime is not 100%. There is a timer or something in the ECM that prevents it from cycling the pump every time you go from key on to key off and back. Not sure how long you have to wait, might be a couple seconds, but it's a pain to use that reliably.

I think it was mentioned in the other thread, if you put 12V to the red pigtail hanging off the fuel pump relay, that tan/white wire should have power constantly. But you could do the same thing without 12V, just check for continuity from that pigtail to your tan/white wire.

Yes you can run a carb, but it's enough work that I'd invest the time/money in getting TBI up and running instead.

What do you need for the TBI? I am pretty sure I've got a nearly complete SBC TBI setup in the garage (can't recall if that includes fuse panel or just underhood wiring) that I'm not interested in taking up space. Don't recall if it's the new front end style lights or the older.
 
I did the pigtail test and there was no power on the tan/white wire at the pump. I checked the ground on the relay and it's good, checked the power at the relay and it's good also. I need the tbi and the trotted body and the wiring harness.
 
That red wire bypasses both the relay and the oil pressure switch, so something is wrong.

How is that red pigtail connected to the relay? Does it use one of the relay pins to get to the tank power wire, or is it actually spliced into the tank power wire thus eliminating an internal issue with the relay? I'd still check continuity first, but there should also be continuity from that red pigtail to whatever the tank power wire is coming off the relay. If there isn't, the problem is there.

Is the tan/white wire the same at the relay as the tank end? I apologize for the basic questions, I just can't remember some of this stuff. If it is, I'd check it for continuity from the relay back to the tank to make sure there is no break in it if it checks out on the relay side.
 
It's not spliced in it runs through the relay. Going to check the output of the wire right at the relay once I get back to the house. The tan/white wire is not the same at the relay. I will post a schematic of it here when I get home.
 
Maybe the relay is bad internally, or that connection is just bad. It's not like the relay has to operate to provide power from the pigtail (490), but the only way it's not getting through is a bad wire, connector, or internal relay issue.

Check continuity of wire 490 from end to relay plug terminal, if that's good, then check continuity between pin C and E. If nothing, relay is bad internally.

This an AC rig? I don't recall on the R/V series, but the '88+ C/K used the same relay for AC as the Fuel pump, and right next to each other, so testing one with the other is easy.
 
Yes this is an A/C rig, but the previous owner removed removed the AC components. There is a spot for another relay right next to the fuel pump relay, but nothing is there. Getting ready to head out and put the new fuel pump relay in and do some checking.
 
Ok, got the Fuel Pump relay on and now I have power going past the relay, still no power to the pump but I did find a break in the gray wire that down the line becomes the tan and white wire for the fuel pump. Searching for the other end of the wire as we speak.
 
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FOUND IT!!!! The factory splice in the wiring harness had pulled apart right here. The gray wire going to the fuel pump relay pulled clean out of this splice Put a jumper from the POSITIVE terminal to this splice and BOOM, power at the pump. Now to fix it. Problem is it is right behind the distributor. Going to be a pain getting to it with out taking out the distributor OR trying with just taking the cap off.
 
Yep tomorrow should be a productive day, if the old lady can stand it. I get my fuel tank, sending unit, tank straps and pump tomorrow. Going to solder the wire connections tomorrow and do one more check of the wires, then the aforementioned items are going in. I couldn't have done it without those FSM's. I appreciate it greatly.
 
Well folks, ran into another issue. When I use the prime pump wire on the fuel pump relay from the battery, the pump runs strong and loud. However if I turn the key over or try to start the truck the pump doesn't kick on. Am I missing something here? I figured it would prime the pump for a few seconds, or at least kick on when trying to start.
 
Older post, you get it figured out? Unless the switch and relay both failed, either one failing should not cause a no-start condition. Dumb question, you've checked the fuse?
 
Yes I figures it out. There is a pink and black wire that runs from fuse bulk head connector in the engine bay. It's sole purpose is to give power to the ecm for the fuel pump relay, oil pressure switch and the fuel pump. It was cut about half way through the engine bay. There are two pink and black wires coming from the bulk head connector, one powers the ABS circuit and the other powers the ecm circuit for the fuel delivery.
 
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