84 720 pickup, fuel pump

[AZscout]

Hey there gents

Got a little problem with the fuel pump for a 1984 Nissan 720 pickup...I had a fuel issue and the shop replaced the original fuel pump with a "carter" manufactured fuel pump...worked for 'bout a month and then the truck started acting like it was starving...ran the fuel lines (good) and fuel pump and all relays (good) but after driving it several miles 5, 10, whatever...the engine cutsout and the fuel pump seems to be hot to the touch and no fuel in the carb window...at this point the truck won't start....at this point I have to disconnect the fuel pump on the output side and at the line leading into the carb, turn on the key, fuel pumps from the output side...reconnect that...fuel pumps from the hose to the carb, reconnect that and voila, the truck will restart...all this just to repeat itself at another inopportune moment...any suggestions, pls

[PEZi]

sounds to me like it might be a clogged fuel filter causing it... or something stuck in the line before the pump

[AZscout]

I checked that also...fuel filter and lines are new and clear....The engine restarts immediately after I "break" the fuel lines and turn the key back on and reconnect it all...

[captainzeros]

Just a thought, but junk floating around in the gas tank can cause intermittent problems like that. If a piece of crud gets sucked up against the fuel pickup inside the tank it'll block any fuel from getting to the engine, and pulling off the hose might be just enough to get a piece of crud to fall back down away from the fuel pickup due to no suction just to be pulled back up again after running the engine some.

This is just a guess though, I'd probably wanna try any easy solutions and wrack other peoples brains more before dropping the tank and boiling it out cause that's a lot of work for a hunch.

[AZscout]

I'll keep it in mind...last ditch resort...thx

[PEZi]

what's causing it is TBD... but its clearly having to work way too hard to pull fuel if its getting that hot... something before the pump is my only guess

[synack7350]

yeah no its that hot cuz the fuel is probably acting to cool the pump. It's prolly vapor locked ( what it sounds like breaking the line or what not) because the pickup hose grabbed some debris out of the tank. I bet instead of breaking the lines if you let it set awhile (long enough for the residual vacuum in the line to release the debris on the pickup hose) that after a few cranks the pump would self prime and you'd be up and running again. I think captain zeros is on the money here

[fastboatman29212]

I agree that it is probably debris in the tank. If you eventually rule that out, then take a look at this link. It might help solve the problem if it's a bad fuel pump relay. I would first make sure the tank is clean and free of debris before wrestling with the relay.

http://hubpages.com/hub/The-Datsun-and- ... t-Tell-You

I know I had a broken wire on my stock fuel pump, right where it enters the pump itself. Took me forever to figure out why the fuel pump wouldn't work some of the time and other times was fine. I even removed the pump and hooked it to a battery and it worked fine. Eventually, I discovered that the + wire had broken and was only hanging on by a thread. LOL!

[AZscout]

Ok....so I'm back again, same problem...relays replaced...drained the tank and ran a camera into the tank (thanks to the customs officers) and it's clear free of debris...broke all the lines, ran a check of all lines and filter using hi pressure air...checked the fuel pump (fantastic) and reconnected all the lines, primed the system...runs for about 15-20 mins (with a little herky-jerk) and dies...check the carb and lines...zilch on the fuel (from the carb back to the fuel pump)...break the fuel line at the output from the pump, turn on the key and voila, pumps like 40 year old virgin who just saw his first porno...reconnect and we're up and working until it happens again and again and again...WTF...something hooked up wrong?...vacuum on the pump?...replace the new fuel pump?...The one that's installed is just a fuel pump with no reservoir, nothing like the old stock fuel pump, its a carter, one input and one output

[MetalFab]

Wow if you've gone to all that effort and it still is acting up.. My only thought is to try it with the gas cap off with half a tank or so and no sharp left corners =) Perhaps your breather line to the charcoal canister is plugged? Or next time it happens try taking off your gas cap and see if it'll fire back up. Sounds like it is building up vacuum until the tank and the pump are fighting each other, the tank being the victor and pulling fuel/air back down the line somehow from the carb therefore being dry when you go to check it.

[synack7350]

wow good thinking metalfab. should hear the vac release when you pull the cap if thats the case too.

[flinterman2000]

If there is no vac release, try using another fuel source. A temporary tank or gallon bottle. Remember this just to check if the tank is the problem.

[Magnetorque]

Check the fuel filter inside of the fuel pump assembly itself. Go the the fuel pump assembly mounted on the frame and unscrew the bottom access plate. I believe it takes a 17 mm wrench.