1981–1985 Nissan and Datsun Pickup Fuel-Pump Problems

Updated on January 25, 2019
dlarson profile image

Dan has been an auto mechanic, truck driver, engineer, and many other things.

This article is for owners of the 1981–1985 Datsun or Nissan 720 pickups with the electric fuel pump. On this page, you will learn how to go beyond the typical service manual fuel delivery problem diagnosis.

If, like me, you have trusted in your Haynes manual to troubleshoot a fuel delivery problem, you may have found that nothing seems to work and the problem persists. You’ve checked the fuse (#2) and it’s good! You’ve checked the output of your electric fuel pump (just in front of the passenger side rear tire) and find that it works most of the time—or maybe it only works if you power the pump with a jumper wire! Yet, your pump just won’t put fuel to the carburetor when it’s supposed to . . . or it will for a while, but then the truck dies and leaves you stranded for 10–15 minutes, or until tomorrow.

It is likely that the trouble lies in your fuel pump relay. Now I know that the book doesn’t say anything about a fuel pump relay, and many mechanics don’t even know about it (they’re probably using the same book). I'm here to tell you that the relay exists and should be called a fuel shutoff relay. You will also find that the auto-choke relay is mounted on the fuel pump relay. Trust me, it exists (don’t believe Chapter 13, figure 5.2b). I have a 1981 Datsun and a 1984 Nissan and they both have this troublesome black box. Your repair guide not only ignores it, but it is conspicuously absent from the wiring diagrams, making diagnosing and repairing electric fuel pump problems virtually impossible. I tore apart my wiring harness to discover it and later found other shade-tree mechanics discussing it in a few online forums.

Look Under Here!

To find it, look under the dash on the passenger’s side. It is just visible above the kick panel in front of the door and will have the auto choke relay attached, and in automatic trucks, the fuel cut solenoid.

Look Closer

The fuel pump relay itself has a 6-pin connector going into it. Those are six wires that you will not find on your wiring diagrams. Do not try to remove the harness from the relay unless you have forearm muscles like Popeye. Remove the attached relay(s) and then undo the two screws holding the fuel pump relay to the panel. I found it easiest to remove the knee bar and heater blower motor first, but if you have very short screwdrivers and small hands, you can probably manage less disassembly than I did.

Wiring Diagram of Relay

B=black, W=white, L=Blue, G=green, and Y=yellow.
B=black, W=white, L=Blue, G=green, and Y=yellow.

These six mystery wires monitor several important systems in your truck so that if any one of them fails, the electric fuel pump will not run. Before you unbolt the relay and spend $50 or more to replace it, first make sure that these systems are functioning correctly!

They are:

  1. The ignition switch accessory position (power to blue wire when on).
  2. The ignition switch start position (power to white wire at start using fuse #5).
  3. The alternator (power to white/blue wire when running).
  4. The oil pressure switch or oil sending unit (4WD) (yellow/green).

This is a wiring diagram for the fuel pump relay terminal that I created using the Haynes color codes found in my harness. Hopefully yours is the same. Use this to check continuity in your wiring. It’s better to find a broken or corroded wire now than to replace the relay and still have the same problem.

Repair Manual Discrepancies

I’ve noted some discrepancies in my Haynes manuals which may or may not apply to yours as well.

  1. The wire from this relay to the body harness connector (ultimately to the fuel pump) is white/black. Why Nissan used a white/black wire from the relay to the body harness connector (found under the carpet beneath the passenger’s seat) is a mystery to me. All other fuel-related wires throughout the truck are brown as is the connecting terminal in the body harness connector which goes directly to the fuel pump.
  2. The white wire connects to the fuse block at fuse #5. In my two Haynes books (chapter 13, figure 3.1b), fuse #5 is shown to be empty. I’m currently running a 10A fuse in this position and haven’t had any trouble. Also, pulling this fuse doesn’t seem to shut off any start features other than the fuel pump (via the relay).
  3. Not related to the fuel pump relay so much (but since I’ve breached the subject) the wire out of fuse #1 (ignition coil no. 2) should have been listed as WB and not WY. All other diagrams seem to show it correctly.

Test Your Fuel Pump Again

If you have not already tested your fuel pump by running a jumper wire to it, you can do it now. Build a short jumper wire and connect the blue terminal to the white/black terminal. When you turn the ignition over to the accessory position, you should now hear the fuel pump running constantly (not recommended as a permanent fix)!

The Fuel Pump "Shutoff" Relay

If you decide to buy a replacement, go with quality parts.
If you decide to buy a replacement, go with quality parts.
The red arrows indicate the contacts that probably need repaired.
The red arrows indicate the contacts that probably need repaired.

Assuming you’ve narrowed down your problem to this relay, you can order a new one from an online parts warehouse or your local dealer. However, you may be able to save a few dollars. What have you got to lose trying? The relay is already not working and you’re a do-it-yourselfer after all!

  • Here’s your little trouble-maker once you’ve removed it from the truck. A factory relay is labeled Jideco, and if you choose to replace it, they seem to last about 20 years.
  • On the back of the assembly are four Phillips screws. Once removed, the cover and insulator come off and you’re looking at the circuit board of the relay itself. On the opposite side are the resistors, amps, and the big coil that should trip the relay when all is well—but has probably failed. If you look at the solder points under magnification, you may notice cracks. If you’re careful, you can resolder these contacts and have your relay working again in a few minutes.
  • Now put it all back together, pat yourself on the back, and go for a drive. You just potentially saved yourself hundreds of dollars at the dealer!

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

    © 2009 Dan

    Comments

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      • dlarson profile imageAUTHOR

        Dan 

        8 weeks ago from Priest River, ID

        Clide. Check the pickup tube from the fuel tank. Sounds like it's cracked or plugged.

      • profile image

        Dwayne Oxford 

        8 weeks ago

        Clide Tshuma did you not see above article?

      • profile image

        Clide Tshuma 

        8 weeks ago

        I'm sitting here with my nissan 1400 1985 model is not pumping fuel to curburater but when you fill 2 litter bottle with petrol it drives well I need your help

      • Dwayne Oxford profile image

        Dwayne Oxford 

        9 months ago

        See no way to reply to questions/posts here, but those of you having probs with Nissan 720's need to be at 720 World.

      • profile image

        Tim 

        10 months ago

        Need help

      • profile image

        bcstoy - carburation part II 

        10 months ago

        I rebuilt the carburator in the 85 4x4 and repaired the rounded plug connector. Still engine did not want to idle it would run erratically and died. Then I proceeded to check the electrical circuit. Disconnected the black plug at the ECU. I checked for continuity at terminal 4 in the plug. You should press the clutch pedal and have continuity while the pedal is depressed but not once it is released. In the same terminal switch the tranny shifter to any position other than neutral you should not have continuity. Now check for continuity at terminal 6 with the accelerator pedal you should see continuity, release the pedal and should have no continuity. All these tests are done to ensure that the shut off system is working properly. If any of these tests fail then the truck will not idle because they actually control the idle stop solenoid.

        To check the idle stop solenoid you should turn the key on and check for power at the red wire for the solenoid. Or if powered directly from the battery you should hear it clicking. There is a possibility that the solenoid may work when connected directly to the battery but not when is in the circuit. If in doubt you can buy it in e-bay. In my case I also had a defective neutral safety switch. The are between the carburator and the manifold seems to be prone to vacuum leaks. Install all new gaskets, one before the metal plate another after it and another after the mixture heater making sure all surfaces are clean and straight specially the metal plate. If you do all these things you should have a good running vehicle. In my own experience I do not tear the whole carburator, I just open the top and the reservoir use carb cleaner and compressed air making sure all the internal are clean and where they belong. Keep an eye on the little spring, cylinder wight, and the ball for the accelerator nozzle. They go in that order. I rebuilt two carbs and both either had no check ball or the little spring was missing. Also check you float to make sure that is horizontal with the carb upside down, the distance is about 7.5mm. I decided to write this comment given the bad rap about hitachi carburators. I was frustrated and nothing at ratsun helped me. Do not confuse the air jet, the primary has a number 50 and the secondary has 100 stamped at the top. I usually take one at a time. If you have problems shoot me an e-mail: bsctoy@aol.com

      • profile image

        bcstoy 

        10 months ago

        I thought I share my experience with my project. A nissan 85 4x4 x-cab. It was a mess, I replaced the engine had the wrong carburetor with the two wire connector. The previous owner blinded the rounded plug wire harness. Got the right carburator and the problems began.

      • profile image

        Rod Hancock 

        11 months ago

        1984 720 truck, same problem with fuel pump relay. Installed new one (cheapo) and it failed after about 1000km. Going to use your advice and buy a Jideco, but will open up cheap one first to see if there is a quick fix. will also jump ground to fuel pump to assure all that wiring is good. Already checked pump with 12volt source and works fine.

      • profile image

        need answers 2018 

        12 months ago

        . hi , i looked under passenger side dash and find only a paired blue and black relay (total of 2 ) and removed them to look beyond,this area but there is no additional jideco relay device hiding up there . i even took the vent duct work off as well. there is no wires even heading up there for me to trace, to locate the jideco relay . is it possible a 1981 nissan 2wd automatic z22 , has this hard to reach shut off relay located somewhere else other than this location ? , i am also going to do the fuel pump "possible corroded damaged copper" inside of insulation coating ,... to test the integrity of wire right at point where wiring enters fuel pump body on frame , to test if it has corroded-copper-weak-contact and will repair if needed ,.. i thought it would be easy to find this relay by just looking for wiring and following it up to relay, but there is no wiring to follow and no relay to be seen, i also looked above blower and there is a fan wire and some vacuum lines for vent and control manifold, but there is no jideco relay up in there . so i wanted to ask if maybe this hard to find relay is located under dash on driver side or hidden in console or any other suggestions of where to look, i did remove the blue and black relays from their harness and turn key on and the fuel pump still functions, .... the reason i removed the blue and black relays was to listen to hear a jideco click or anything to help me locate the jideco relay, but i can hear nothing up under passenger side dash. i hear only the fuel pump mounted on the frame by passenger side rear tire , .....things i have done so far , dropped tank down , cleaned it inside and out , . new fuel float , replaced all the houses and the 2 filters around tank and fuel pump area ,. and i still have the fuel cutting out when acceleration up to speed issue,...the truck revs fine in neutral , but once in gear and driving , i cant get over 30-35 without bogging down sensation , which comes and goes ,..... i am going to do the brake clean spray in engine compartment when engine is running ,,to test for vacuum line leaks- the test we have all seen on line . incase i have a failed hose that needs replacing .

        . . . on the nissan parts schematic link ,it shows a jideco relay and states only after nov of 82 the jideco is located way up under there. but i could be reading the schematic incorrectly . so i am asking for help.

        see https://www.megazip.net/zapchasti-dlya-avtomobilej.../il-56175398-8108326-8108326

      • profile image

        Hector 

        12 months ago

        Hi there,

        In the wire description, there are a wire that you mark as Oil Switch, how do you deduce that is from Oil ?, I belevide that this wire came from the Carburator deposit , once the depositi get full the floating stop sending signal to the relay to stop the gas pump, I'm right ? ... if not, how the pum si stoped to avoid ovelr fill the deposit of the carb? ...or does the pum is pumping all the time once the start switch is open ? ... thanks

      • profile image

        kennygriffin 

        13 months ago

        i have a 85 nissan pickup,what i would like to know how can i disable the gas shut off,my fuel pump load the carb and crank, by dies in a minute,something is shutting off the gas supply,any help woud be apprecated

      • profile image

        Ari Falco 

        15 months ago

        I wonder if my faulty fuel pump relay can affect the ignition system on my z24s engine...?? ..I have low/fluctuating current to the ignition coil since the fuelpump relay stopped working...!!..the fuel pump works when engine running but not when ignition switch is on !!

        My engine is a z24s , carburetor , breaker point ignition , singel coil , 4 plugs....no ignition control that i know of....cant find any wiring digram for this

      • profile image

        Oscar 

        21 months ago

        Carb rebuilt gas tank cleaned replaced 3 fuel pumps and still dying out my 82 nissan datsun 720 still does not want to stay on any suggestions

      • dlarson profile imageAUTHOR

        Dan 

        23 months ago from Priest River, ID

        See if the wire going into the fuel pump is fatigued and losing contact. I was trying to diagnose this problem and my wire pulled free from the pump. It was so corroded that it was only making an occasional contact and was really broken just inside of the pump.

      • profile image

        Tanya 

        2 years ago

        My 85 nissan sputters when i push the break down what could cause that to happen

      • profile image

        ingeislas 

        2 years ago

        please could you add some pictures from the PCB top side of control unit 28545 89900 specially of the resistor around the board? as after open it I found some resistirs burned and I cant find its value as erasered the band colored values as burned. thx

      • profile image

        mattsavage 

        2 years ago

        On my 84 720, I can hear the relay engage (several fast clicks in the right side of the dash) when I turn the key to ON position. I finally put 2 and 2 together that it wouldn't start when I didn't notice that noise. That's how I convinced my mechanic that something over there was not functioning properly... After multiple tow trips, new fuel pumps, wiring, etc, over a $1k spent, he finally found that stupid little black box...

        there's no mention of it in the Haynes manual I had, but looking at the wiring schematic, you can see it...

        Thanks for this post!

      • profile image

        Larry 

        2 years ago

        Ok so I had a 85 720 that would run a bit then die, I went to a local junk yard and bought a used wire harness section that runs from fuel tank to under the passenger seat and it was fixed , obviously a wire failure probably from age and exposure.

      • profile image

        Boeken1986 

        2 years ago

        I have a 1985 nissan 720 that was cutting off like no fuel after about 10 mins and starting back after about 10 mins so i change the fuel pump fuel filter and the fuel pump relay and now it started but died when i tryed driving what else can it be

      • profile image

        matt 

        2 years ago

        All the same symptoms with the pump relay. I tried the jumper. But got no results. Any suggestions

      • profile image

        Danny 

        2 years ago

        I don't think I have one or I'm looking in the wrong place. I have an 81 4x4. I do hear a relay when let go of the gas but it looks like a regular relay. Can I post a pic here?

      • profile image

        dj 

        2 years ago

        My 84 2.4l starts fine when cold. Eventually acts like no fuel, but can hear the fuel pump running. Pour gas down carb and it restarts instantly. Have to hold a high rpm when pouring gas into carb, then starts running again. If a not holding a high rpm, it burns gas off and dies again. Might not start until cold again. Could it be anti-dieseling solenoid? Is this solenoid also driven by relay?

      • profile image

        jrock 

        2 years ago

        back at it with light problems... all my lights work but no tail (running) or licence plate light.. checked bulbs fuses ect.. im at a loss here. brake lights and reverse lights work as well. dash lights are working as well. any ideas?

      • profile image

        Tacy 

        2 years ago

        Just bought a 82 king cab Nissan pickup 5 spd. Spits and sudders, put seafoam in and is worse. Any suggestions

      • profile image

        Anthony 

        2 years ago

        1985 nissan 720 2.4 liter. Fixed a hole in my gas tank unhooked fuel filter and all to drop the tank put everything back and filled it all the way up turn key on and I hear the fuel pump turns on but no stsrt so I check filter and no gas is going to filter or pump...??????

      • profile image

        dzachareas 

        2 years ago

        You rock! Thanks for this, it is a huge help!!

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        jrock - My guess is that your parking light power wire has either blown a fuse or fatigued where the wire makes a tight bend coming out the back of the fuse block. If the fuse is good, unscrew the fuse block and look at the wires coming out the back of the fuses.

        Zack - Sounds like your carb is gumming up. Switch to a non-ethanol fuel source to see if that clears it up. The ethanol breaks down the rubber seals in the carburetor and fuel system as well as it attracts water and causes the steel bits to rust. There is no good reason to use an ethanol-laced fuel in any vehicle, especially not these older rigs.

        Allyson - Sure sounds like the fuel pump or the fuel pump relay! You came to the right place - I hope you found the answers here you needed!

        jrock - Don't have any experience with swapping carbs - except for swapping to the Webber. I've been using the webber for years and am still very happy with it.

      • profile image

        jrock 

        3 years ago

        Any ideas why I wouldnt have dash, tail, or runninh lights but have head lights? They just stopped working. I check all the fuses and connections all look good im stumped

      • profile image

        Zack 

        3 years ago

        I have an '82 King Cab automatic that runs great (for the most part). After sitting for a day it'll start a little rough, then hesitates a tiny bit while it accelerates but never dies while driving. Then after driving around for 20 minutes or so, it runs perfectly smooth and starts back up like normal. Does that seem like it might be the relay?

      • profile image

        Allyson 

        3 years ago

        I have a 1980 Nissan Datsun 720 King Cab and love it! But I drove it for about a week and when I was pulling out of my driveway yesterday, I got a half a block and the beast died on me! I notice that it doesnt make the same ticking sound the electric fuel pump used to make prior to turning the engine over? Any thought? It sounds like she really wants to start and when my wife sprayed starting fluid in and around the carb it turns on and shuts off right after that?

      • profile image

        jrock 

        3 years ago

        found a cheaper carb on ebay from bochione car accessores was wondering if there worth a hoot? it also has the 2 prong plug in mine has the one with 5 or 6.. would this work for my truck? thanks

      • profile image

        Jmontz 

        3 years ago

        Thanks for this post. I've had the same problem only within the past few months. Hopefully I can troubleshoot the problem now that I know more about the whole fuel system. You all are the greatest Nissan owners ever.

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        Bill: the relay typically starts failing after about 15 minutes. Sounds like it might be your culprit. After the truck cools it probably runs okay for another 15 minutes? Try the bypass to see if its not the relay before spending more on this problem.

      • profile image

        Bill 

        3 years ago

        My fuel pump runs but by the time I put it in third gear it acts like the fuel is cutting on and off. It`s almost like cutting the switch on and off while you`re driving. It`s got a new carb.

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        Sounds like you have Ethanol laced fuel in the tank. It turns to gel and will clog your fuel system. You'll have to disassemble the tank, pump, lines - pretty much everything to clean it out.

      • profile image

        Scott Storkson 

        3 years ago

        Have a 95 Nissan pickup been sitting for three years will start if I leave key on for awhile but die fairly quickly

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        Realistically, it will work for years. The danger is if you do get in an accident, the fuel pump will keep running - potentially pumping gas onto a hot engine or fire. It will run as long as the key is on and the battery connected. Not a good situation.

      • profile image

        jrock 

        3 years ago

        i noticed you said a jumper wire isnt recommended as a permanent fix but how long will it work? i been tapping mine with a screwdriver and that works most of the time but i was thinking about just jumping the relay till i get a new one..

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        If the relay is sticking open or closed, I would highly suspect it.

      • profile image

        jrock 

        3 years ago

        the fuse just didnt wanna stay in the connection is gapped to much.. i just took a thick piece of copper wire and stuck it in with the fuse so it stays tight. and i belive the relay is the problem if the truck dies i hit the relay with a screwdriver and the pump works again. i noticed that the pump seems to always run, is that normal? thanks for all your knowledge

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        Sounds like you might have a short in the wiring harness or back of the fuse block. Let us know if you find the problem and it's something other than the carburetor!

      • profile image

        jrock 

        3 years ago

        mine doesnt die going up hills usually just when i let off the throttle but im thinking the carbs going bad as well.. been tryin to put strictly non ethanol in it but im also haveiing fuel pump issues which let me to this page.. going to check out that relay now. i noticed my wiper/washer fuse (#6) wont stay in.. when its not in the fuel pump runs in the on position on the ignition rather then and when i wiggle it, and the wipers start working i hear a click in said relay and the fuel pump shuts off

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        It sounds like your carburetor is going bad, possibly from the use of Ethanol fuel. The stock carb is not designed for ethanol and it will corrode and destroy the carb. My truck ran the same, eventually dying when I would try to climb hills or put a load on it. I had to replace it with a Weber carb.

      • profile image

        jrock 

        3 years ago

        i think i need a new one of these relays as well, ive had the same issue with the dieing and such.. but aside from that, all of a sudden my truck decides it doesnt want to idle.. almost as soon as i let off the throttle it dies.. i adjusted the throttle position screw a little and got it to idle, but then it started to diesel once i shut it off. backed it back off enough to get it to idle still ,and stop the dieseling but that only worked for a few days.. ideas??

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        Sam,

        There is a weak spot on the fuel pump wiring where it leaves the pump body. I would make sure you're getting good contact there also. When I tested mine, the positive wire was so corroded that it broke off at the pump housing. I drilled out the corrosion and jabbed a clean power wire back into the hole, then taped it in place. That was 2013 and the truck is still running.

      • Jim Cottengim profile image

        Jim Cottengim 

        3 years ago

        great info on the Unmentiontioned relay

      • profile image

        Sam on the river 

        3 years ago

        It turns out I'm also having issues with the relay located next to this one. You mention that there is the fuel cut solenoid located here, in auto. trucks. Mine is manual '84 720 2.4 l, with dieseling issues after turning off the car. This problem is exacerbated now that I have removed this relay, which is the smaller standard (like AC, horn) with 5 terminals. This leads me to believe it is also a fuel cut connection.

        I've replaced the discussed fuel pump relay, which was causing issues, and as mentioned in different comment, I jumped the blue/blk,wht connection to drive myself out of a bad spot.

        After replacing that relay, this other one started clicking like crazy. NAPA has one on the way for me tomorrow.

        Do you think it's a relay for, or maybe IS the fuel cut solenoid?

        Thanks again for your helpful article.

      • dlarson profile imageAUTHOR

        Dan 

        3 years ago from Priest River, ID

        Zach - I'm going to say you have a short in the wiring harness somewhere. Look for a wire rubbing on the body or frame. The wires from the pump pass through some areas of the frame that can rub or easily get pinched by a stump or rock when off-roading. Also check under (behind) the passenger seat where the harness drops through the cab. If I remember correctly, they run close to the transmission and if you've replaced the clutch, could have gotten damaged there as well.

      • profile image

        sam on the river 

        3 years ago

        Thank You!!! Jumping the terminals on the wire harness saved by butt today as I could not get a replacement relay.

      • profile image

        Zach Hutchinson 

        3 years ago

        My 82 just keeps blowing the 2nd fuse and I've replaced the pump and had to wire my brown to my positive wire from pump and hooked the black to ground to pump and that's it and it's blowing fuses every 5 min

      • dlarson profile imageAUTHOR

        Dan 

        4 years ago from Priest River, ID

        No spark or no fuel? With the dual coils, its rare to lose all spark, but i have fouled all the plugs when i was having càrbutor issues.

      • profile image

        william 

        4 years ago

        I have 85 nissan 720 z24 i got the fuel pump fixed now im not getting any fire anything u can think of that might get me off the side of the road

      • profile image

        shannon 

        4 years ago

        Thank you for your help. We will do the things that you suggested and hopefully it will work. Now the blinkers won't work, the speedometer doesn't work or the gas gage. It seems like one thing after another with this truck. Any ideas? The headlights work, high beems, horn, ignition. Not sure what it could be. Again, thank you for your help!

      • dlarson profile imageAUTHOR

        Dan 

        4 years ago from Priest River, ID

        You might try cleaning up your carburetor if you can locate a gasket kit for it. Also, locate an ethanol-free gasoline source. Stations that sell "Conventional" or "Ethanol-Free" gas are popping up all over where I live, mostly to serve the boat and/or ATV communities. Never put ethanol-laced fuel into these trucks unless you also put in fuel-stabilizer. There are a couple of really good websites to help you find real gas.

        http://www.buyrealgas.com

        http://pure-gas.org

      • dlarson profile imageAUTHOR

        Dan 

        4 years ago from Priest River, ID

        The typical relay problem is that the truck runs for 10 or 15 minutes, then shuts off. Let it cool for a little bit and it will run again. What you have described is what my truck does when I'm almost out of gas (less than a gallon in the tank perhaps). Anything more than partial throttle makes the truck sputter and eventually quit, but it will start and run for miles if I feather the throttle.

        This sounds more like a carburetor issue or a blocked line in the fuel tank. If carburetor, the factory system was not designed for fuel containing ethanol. The ethanol will destroy gaskets and rubber components (fuel lines for instance) but also attracts water, causing corrosion in the fuel system. These carburetors are not simple and I did a Weber conversion on my truck (which I did photograph but didn't write up).

        I would first do a fuel flow test - disconnect the fuel line and make sure the pump is working well by turning the key to make it pump into a container. There is a flow rate specified, but if it pumps uninterrupted, it's probably a good pump.

        Assuming that is all good, the carburetor is the next likely culprit. My truck sat for 7 years before I bought it and the fuel had not been drained. It would run fine if I babied it everywhere. Like you're experiencing, under load or heavy acceleration, it starts to run too lean (like it's out of gas). I didn't experience the erratic idle, but had enough trouble with the factory carb that I swapped to the Redline Weber kit (minus the air filter) for about $300. There is a performance kit and an economy kit - I went eco and get about 15-17 mpg, about the same as the factory carb but without the lurching and backfiring. When I called Redline for support, I actually talked to someone in America who was himself a mechanic! It took about 2 hours to do the swap.

      • profile image

        shannon 

        4 years ago

        Yes it did. So now this is really confusing, my son was driving it yesterday, we have not replaced the relay yet, but he said it was driving great, except when he would go up hill it would sputter real bad, loose power so he would pull over turn it off, turn it back on and it would run fine until he came to another hill. It also seems to be turning the idle up on its own. He has to keep a screwdriver with him so he can adjust it. Do you know what might be causing this? I really appreciate your help.

      • dlarson profile imageAUTHOR

        Dan 

        4 years ago from Priest River, ID

        The factory location for the fuel pump is just forward of the passenger-side rear tire. There should be a steel shield around the pump, but most of them get removed when the pump is suspected of problems. Hope this helps!

      • profile image

        shannon 

        4 years ago

        We bought our son an 84 Nissan truck, king cab 4x4 with 2.4 liter engine. It will start but when you slow down for a corner or for stop sign it dies. So I was very happy to find you article. When we located the fuel pump relay, we noticed that the wires that were supposed to be plugged into it actually had a fuse plugged into them. So we took the fuse out plugged the wires into the relay and it did the same thing. So we will replace the relay and will see what happens. The question I have is the fuel pump behind the rear passenger tire the actual fuel pump or is it an after market pump that someone put in to bypass the real fuel pump?

      • dlarson profile imageAUTHOR

        Dan 

        4 years ago from Priest River, ID

        I've recently had similar trouble and found the break in the wire where it goes into the pump. Hope you find it easily!

      • profile image

        Francisco 

        4 years ago

        My 86 nissan has the five relays on pass. Fender wall .... Fuel pump, main,p.t.c,inhib, and check relay. Fuel pump doesnt turn on when key turned. Dropped tank took pump out of tank, ran 12v to the br and blk wire and pump didnt run? Wires were cracked up so im guessing the pump is bad. Truck has been sitting 2004

      • profile image

        Dasis 

        4 years ago

        I have a 85 720 4x4 z24, mine will start fine, run for just a second and die unless I give it gas, I replaced the anti-diesel solenoid/idle stop solenoid, and replaced the fuel filter, all fuses are good, when cold it idles up to like 3,000 rpms, pat the gas and it drops to like 1400, when it warms up it dies, it runs fine other than it will not idle, would the relay cause this or is it something with the carb?

      • profile image

        D. Cook 

        4 years ago

        Thanks to the author of this well written much research article I was quite easily able to track down the problem and fix it without a great deal of know how. The essay took me right through everything and gave me a very satisfying conclusion...

      • profile image

        mark stafford 

        5 years ago

        to the person who put the fuel pump relay info for 86 nissan 720,,,i want to say ,,YOUR THE BEST !!! AND THANK YOU!! we need more people like you !! it was a big help.and i will pass this on !! thank you !

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        Good call on loss of suction!

      • profile image

        Matt custer 

        5 years ago

        Update on my beast dropped the tank again n replaced all the rubber gas line n she runs strong again!!!! Had a nice Lil slit around the clamp

      • profile image

        Matt custer 

        5 years ago

        I did what ya said n blew through the return line with my compressor. I've even took the gas cap off n still does the same thing probably tomorrow some time I'm goin replace the other to rubber hose's I've replaced the one

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        Now I'm intrigued. Tank is clean. Pump works unless connected and pumping for some minutes. Is the fuel return line clear? It shouldn't matter... Opening the gas cap didn't solve the problem? It seems like the tank is getting under vacuum at some point and the pump can't pick-up fuel with a competing vacuum in the tank. That takes the thinking back to the fuel return line or the vent line (to the charcoal canister).

      • profile image

        Matt custer 

        5 years ago

        I've pulled my tank n its very clean on the inside.. That's why we figured its sucking air some where

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        I bet the power wire to the pump bypasses the relay. Otherwise, it sounds like your fuel pick-up line from the tank to the pump is getting blocked. If you've had E10 (ethanol) fuel in the truck, there's an extremely good chance the bottom of your fuel tank is rusting - thanks to the alcohol collecting water down there. My next guess is that the pick-up line is pulling up enough rust to block the line.

      • profile image

        Matt custer 

        5 years ago

        I have a new fuel pump on it the pump runs all the time with the switch on. If I put the hose in in a bottle full of gas the truck runs fine but soon as I hook it up to the tank it pumps the fuel for a min then it stops picking it up out the tank is it possible I have a hole in one of the gas lines?

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        Sounds like the relay has been bypassed. Does it run continuously with the key in the run position but the truck not started? If the relay is bypassed and you still have an intermittent pump problem, I would still suspect the wiring or the pump (although I believe you have a new or re-man. pump).

      • profile image

        Matt custer 

        5 years ago

        I took my relay out n unplugged it n the fuel pump still runs figured it would shut off after I unplug it

      • profile image

        Matt Custer 

        5 years ago

        At first the pump would run but wouldn't pump any gas it would then it would stop picking up the fuel now it just cuts off for awhile or till the next day

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        I misunderstood. I thought the pump was running but not pumping. If the pump is shutting off after a few minutes, it's most likely the relay!

      • profile image

        Matt Custer 

        5 years ago

        It definitely aint the wires from all the comments I've been reading it acts like the relay it will run 5-10 mins if that then shut off then 1hour later or the next day it starts working again

      • profile image

        Mobile dlarson 

        5 years ago

        I had a similar problem and had to replace the wire to the fuel pump itself. Inside the insulation, the wire had corroded away to green powder. I could jiggle the wire and get it to work for a while, but it finally broke completely off. I suspect the two wires at the fuel pump.

      • profile image

        Matt custer 

        5 years ago

        It pumped gas for a couple mins then it stopped put it in a thing of gas it was running then the fuel pump just shut off n now not cutting on

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        How long does it pump gas? The relay will shut off the fuel pump if it's not getting signals from all the input wires. If the alternator is not charging or the oil pressure unit is not sending a signal, it will shut the relay off after a few seconds. Does it pump gas when you have the key almost to the start position (but not far enough to hit the starter)? I tested mine by disconnecting the fuel filter and putting the line in a gas can.

        Also, make sure you have a good ground and that fuse #5 is good.

      • profile image

        Matt Custer 

        5 years ago

        OK I put it all back together n the gas cap off n it still stops picking up the gas

      • profile image

        Matt custer 

        5 years ago

        Thank ya for the help I'll try that

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        Try disconnecting the return line to the fuel tank after the canister. I'm not near my truck or books but I seem to recall it's like a vacuum line running back to the tank. I believe you can blow air back to the tank and by listening at the gas cap, see if the line is clear.

        If you still suspect it's the problem, try leaving the gas cap off (or loose) to see if the problem goes away while driving.

      • profile image

        Matt custer 

        5 years ago

        Is there anyway to check the canister to see if it is stopped up some how

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        Make sure the fuel line is clear and the return line as well. Also, try opening the gas cap next time it won't pick up fuel and see if it starts pumping again. I'm wondering if the canister on the drivers side of the engine compartment might be plugged (part of the emission system). This is a one-way valve that allows air into the fuel tank while the fuel pump is working but doesn't allow the gas to evaporate. I'm guessing the tank is developing vacuum and stopping the flow of fuel.

      • Matt Custer profile image

        Matt Custer 

        5 years ago from Catawba, Virginia

        I have a 85 Nissan 720 truck I just replaced the fuel pump thinking it was weak cause not picking up the gas. The pump runs but don't always pick up the fuel that's even with a half a tank any help?

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        That sounds more like a carburetor issue. Have you cleaned the jets and made sure you have no vacuum leaks? Ethanol fuel causes scale and deposits that destroy the older carbs (including varnish). I recommend never running a fuel that contains ethanol. You can find pure gas via pure-gas.org

      • profile image

        Tony 

        5 years ago

        Would this problem be affecting my 1984 Datsun 300zx? It starts and it'll run just fine but as soon as you give it gas it cuts off. I've replaced a ton of parts and don't know what else to do. I hope you can help. Thanks.

      • profile image

        Jm 

        5 years ago

        Thanks for all your efforts and hard work that you have put into this page. It will come in handy for me, and I'm sure many many others.

      • dlarson profile imageAUTHOR

        Dan 

        5 years ago from Priest River, ID

        Joeoe4852: I think you got a bad relay switch.

        Zach: The relay switch does shut the pump off after a set amount of time if the other signals do not become active (such as you didn't start the truck). The pump should come on only when you turn to the start position. If you turn the key towards start, but not quite enough to engage the starter, you should hear the pump turn on and start running. You can hold it there and it will keep running, but returning the key to the RUN position should shut the pump off.

      • profile image

        joeo4852 

        6 years ago

        have a ? thank for the info. on the fuel pump relay switch. I replaced the original one with a new one ran good for a while but seems when the truck has been running for 30 or 40 minutes the relay switch stops working. Have to wait 20 to 30 minutes and it starts again.

      • profile image

        Jim 

        6 years ago

        Thanks for this, I was in a bind this lead me to a 5 minute fix.

        I used my swiss army knife to get the screws under the dash off.

        Unclipped the relay connector.

        Reached back into the depths of my "King" cab and pulled out two spade connectors left over from an alternator/wiring overhaul.

        Twisted the two spades together, jumper-ed blue to black/white and was off rolling.

        A temporary fix as you said but worked in a bind.

      • profile image

        wayne 

        6 years ago

        have a 84 king cab 4x4 manuel 5 speed. ran last year. tried to start it this year with a new battery that i used in a other running vehicle and nothing happened when i turned the key over. my question is could this fuel pump relay if not working effect the ignition switch so that even acceseries wont turn on? I have nothing and see no evidence of mice chewing wires.

      • profile image

        William hill 

        6 years ago

        My 85 720 only has 4 wires and relay Only has 4 pins, bought a new relay which the parts store said was compatible and it has 6 pins, do u think i can use it still?

      • profile image

        thanks 

        6 years ago

        this problem has been driving me crazy for about a year. truck will stall out and then start a few hours later and run ok.

      • profile image

        Zach 

        6 years ago

        Update: i re-soldered a couple cracked connections and the same thing is still happening. I may just run the engine for a few minutes while wiping off the leaking fuel and see if it ever stops. Is it that relay that tells the pump to shut off or does that pump just constantly run?

      • profile image

        Zach 

        6 years ago

        I just replaced my fuel pump and filter and I believe I got everything nice and secure. When i put the power to the truck but dont start the engine, the fuel pump just runs and runs and eventually starts leaking gas from the pump wiring. Does this mean my relay is not working? the truck will start and run but i feel like the fuel pump might still be over pumping. Should I try a new relay? or try to clamp the hoses better?

      • dlarson profile imageAUTHOR

        Dan 

        6 years ago from Priest River, ID

        Wow! I feel good if I get 20mpg. Doing a major overhaul right now and hope to write up bits of it soon.

      • dlarson profile imageAUTHOR

        Dan 

        6 years ago from Priest River, ID

        Very weird! I'd like to know what was happening once you figure this one out.

      • dlarson profile imageAUTHOR

        Dan 

        6 years ago from Priest River, ID

        See if your throttle return spring has fallen off...

      • dlarson profile imageAUTHOR

        Dan 

        6 years ago from Priest River, ID

        My truck has only 2 wires goingto the carb, but you may be looking at an injected carb. If so, the wires are for choke, air mass sensor, injectors, and another write our two down to the exhaust for the oxygen sensor. Keep them all in good shape out convert to a Webber likeI did. I should write a hub on that...

      • dlarson profile imageAUTHOR

        Dan 

        6 years ago from Priest River, ID

        Puzzling... When you say it stops, do you Mann it dies? Is the choke working properly? Possible vacuum leak?

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