Hey all, the ol' girl quit on me for the first time today.... driving down the road and suddenly "OFF"

I had a guy on the side of the road spin the engine for me and I could see that there was no fuel out of the injectors....

Once I finally got home after 3 hours waiting for a tow, I checked some stuff out, here is what I found.

a) no fuel getting to TB
b) fuel pump not turning on
c) used jumper to bypass fuel pump replay... fuel pump still wont turn on
d) unplugged connection at tank (not fuel pump, its about 3 feet of extension from the fuel pump) I used a volt meter to check for power at this point, I got nothing on 3 prongs, the 4th prong had indication of voltage, but very very small, and actually appeared to be pulsing!

From this, I am assuming that the issue is electrical, and exists between the pump relay and the rear connection.... it happened instantaneously without warning.... what could it be? Is there something that could cause this? What do I do next? Thanks very much!

 

Do you have voltage at the relay? If not check the battery connections. There should be a large torpedo connection in the cable between the battery positive and the relay just behind the battery. These connectors have a problem with corrosion.

 

I didnt test at the replay, but I used a wire to bypass it. I connected the jumper from the +ve terminal right to the pin on the replay harness. Normally this would turn on the pump.... today that was not the case. So I think the issue is after the replay circuit...

 

Sorry, my computer auto corrected and turned relay into replay....

 

You must check for voltage at the relay so that you know where to hunt for the problem. That relay controls other things the engine needs to run. If there is voltage at the relay then you will have to check every inch of the wiring between the relay and pump. Will the pump run if you jumper from the battery to the pump?

 

Tomorrow when I have light I will check the power to the relay, but I dont think thats an issue. Is there anything between the relay and the pump? Or is it a straight run of wire? I need to try connecting the battery to the lead on the pump. There are 4 pins, what is the procedure for testing that? (4 pins at the pump connection, not the relay.)

 

There should be at least one junction point where the wires split off to go to all of the things that are supplied power by the ASD/fuel pump relay and at least one 8 pin connector. If you have spark the ASD relay is not the problem as the coil gets its power from that relay.

I do not have an 88 wiring diagram but on the 89 the 14 gauge dark green/black is power to the pump. The 16 gauge gray is the pump ground. The 18 gauge dark blue is the fuel gauge and another 16 gauge gray is the sending unit ground. All of the wires mentioned are that color at the pump but can change color at any of the connections.

Do you have gas in the tank? The reason I ask is that in the 89 there is a low fuel switch in the fuel sending unit, but I do not know what that switch may do. It may just turn on a warning light but it may do other things. I have never run my truck out of gas to find out.

 

Thanks again SEAL, i got it fixed. After I cooled down from yesterday, I went out this morning and checked everything a second time. I had power at the relay, and power at the green wire at the tank. Which means the pump wasnt working. I dropped the tank, and removed the sending unit. I pulled the fuel pump off and bench tested it.... it worked. After close inspection I noticed that the ground wire for the fuel pump in the tank was broken on one side, and the wire had disconnected from the pump itself.... (the little spade connection). I replaced that connector and tested it with tank on the ground and it fired up. Everything is back together now and ready to rock....
I made sure the spade connections were tight to ensure this doesnt happen again. Thanks for your help.

Jacob

 

Or so I thought! ...

Went for the test drive. Worked great for about 5km.... then it started to lose power, bogging down etc.... had to shift down to 1st to limp it to parking lot. Shut it off, went into store, came out. Worked fine again until about 2 km. Then it loses power again.... The more I throttle the worse it gets. Sounds like a fuel pump right?

When I got home, I shut it off, and put a jar to the main line to make sure it was flowing strong.... the pump wouldn't turn on! I kicked the tank, it ran for a few seconds and died....

I then dropped the tank AGAIN, and proceeded to use the fuel pump to cycle fuel into a bunch of gas cans to make it lighter.... I ran the pump for 30 minutes without a problem.... it wasn't under pressure I know but it didnt shut off.... while it was doing this, I wiggled wires, prodded at stuff, and moved stuff around, and it didn't fault once....

I have ordered a new fuel pump, and will put it in monday.... does this sound like a correct diagnosis? Why it is intermittent I do not know. Thanks.