ok, yesterday I had my truck just die, well, kinda like if you turned the gas off on a bike, kinda stumbled then died, but i pumped it and it started right up, got me another 20 miles or so, then I went in and got some pizza, came out, it fired right up and only got me out of the parking lot and barely down the road. which from the past I know is about how long my little float bowl lasts.

so I pushed it back to the parking lot, and went back by the fuel pump, turned key on and tyested the pump with my light and no power to it. checked the fuse and it was good and I tested the wire coming off the bottom side of the block and I had hot through the fuse as well. still nothing at the pump. i started thinking maybe the pump only has power when its running or when you turn to start, but I couldnt crank and test cuz i was by myself. I followed thw wire and found it comes up in the cab under the seat, so right there in the middle of a bk parking lot I ripped out my seat and my carpet, and took apart the plug in the harness right there, found that it was the black/white wire going to a brown on the other side of the plug that fed the pump power, tested it there and still nothing, so I figured a broken wire somewhere between the plug and fuse block. but the wire at the fuse block is solid white so I know it makes some kind of connection somewhere else. gotta be a relay or something I am guessing.

well I grabbed the hot from my amp and jumped it to the pump wire, got the pump going and let it run for a second to get gas to the carb (I know for sure carb was dry before because manually pressing the AP linkage resulted in a spray of air, not gas)

anyways after I got gas to the carb I started it, and I plugged everything back in, and it stayed running long after the float bowl would be empty, so I broke the connection at the pump, and at that point I had hot. but as I was getting ready to leave it died, but i pumped it and it started and got me home. I go to leave to a meeting that night and it starts and almost gets me to the end of the driveway and dies, no gas in the carb again... and yes I have a full tank, topped it off on the way home...

is there a fuel pump relay I gotta check, think its a bad fuel pump (it works fine when hardwired to 12V though)


what shoukd I check.

I love it, my truck is slowly falling apart now or something, few months ago, new oil pressure sender, 2 days ago, new water pump, now something with the fuel pump.

I don't have a manual for that truck, but you're most likely correct...the pump is fine and there's a relay that's gone bad. I just looked up the fuel pump relay on Autozone.com and it's big. Looks like this



It's $50. I would try out one of the $5 30A 4-pin relays and see how that works. $50 for a relay is BS.

I had this problem before on a 84 720. I replaced the pump and the relay underneath the passenger side dash.

alright, Ill check on it tomorrow maybe. I really hope the power in is the same white from thwe fuse block, out is the same white/black, finding ground would be easy and that would leave the 4th wire the switching current. that would make it easy to replace with a different relay. or does the stock one have the diagram imprinted on it just liike the cheap universal ones do?

I cant recall if the diagram was printed on the relay. Every Nissan relay I've ever seen had the diagram imprinted on it.

alright, well I got stuck again yesterday for a while, thought I had it narrowed down to the pump finally crapped. I had my test light out, hot wire from fuse panel to the relay was hot, when I turn the key to start the wire that goes to the pump got power. I put the test light back at the pump using the wires feeding the pump right at the last plug, and turn to start and light came on, I put the aligator clip onto the ground terminal on the pump mount, and left the light stuck in the power wire at the plug and it didnt light, so I took the geround off and scrubbed it and the mount with the wire brush and rehooked it up, and tested it again and thought maybe it had been because that was a bad ground, but it lit up this time and still didnt start, so I tested again using the ground terminal and stabbed the light right through the wire right at the pump, and I had hot all the way back there, but it still wouldnt start. so I was about to have someone bring me a new pump, but for 60 + tax I figured id test it al;l again to make sure, now this time I had no power at all out of the relay. but the weird thing is I didnt get power into it either? maybe I was making a bad connection somehow with the light, because after a few tries I did have power in, and then when the key is turned to on, power out, and then I went and put the lioght back at the pump and this time just wanted to see if it lit but it started, and I got all the way home with no problems.

I figured Id try a relay first since its about the cheapest part and easy to do(universal one) but there is 6 terminals on the oem one...

I know one must be a ground, one feeds the pump, one sends a signal when i turn to start, one has to be the power that gets sent through when the relay opens or closes. im guessing there is another switching wire coming from the ecu maybe to keep the pump goign when its running? because obviously the key isnt always on start, and with key on and no engine running the pump doesnt get power. is it supposed to prime? or since I have a float bowl holding fuel no need right?

what if I were to take a 4 pin relay, just find the always hot that gets fed through, the ground, use the switching source for when its running, the wire out to the pump and bypas the pump on start and whatever else the other one would be, and if I ever had a problem starting it because it doesnt pump while on start, I can just mount a togle switch to manually turn it on for a few seconds before I try starting it again, which I dont think wiull ever happen, even after its sat for weeks, a few ,pumps and the choke and it fires up on about the 2nd crank?

With the economically it's cheapest to run the fuel pump on it's own toggle switch with a in line fuse.

yeah but ill probably forget to turn it on sometimes and have it die on me shortly after I leave. and im sure id also forget to turn it off sometime and have the pump running all night or something. the relay way, while cheap, still leaves me and my memory out of the equation. if I have to flip the switch just to start it for any reason, Id at least always remember to turn it off right after I got it started. or I could get some kind of timed relay and just have a push button to start if needed and not even have to worry about turning it off.

the fuel pump relay was very common for going out..