1981-1985 Nissan & Datsun Pickup Fuel Pump Problems

This article is for owners of the 1981 to 1985 Datsun or Nissan 720 pickups with the electric fuel pump. If like me, you have trusted in your Haynes manual to troubleshoot a fuel delivery problem, you may have found that nothing works.

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)—it works most of the time, or maybe only 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 awhile, 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—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). However, there is such a thing. More precisely, a fuel shutoff relay. In fact, the auto choke relay is mounted on the fuel pump relay. Trust me, it really 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, before I found that other shade-tree mechanics were discussing it in 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 connecter 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!

Comments 101 comments

Zack 3 days 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?

Allyson 2 weeks 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?

jrock 3 weeks 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

Jmontz 3 weeks 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.

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dlarson 6 weeks ago from Priest River, ID Author

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.

Bill 6 weeks 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.

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dlarson 2 months ago from Priest River, ID Author

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.

Scott Storkson 2 months ago

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

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dlarson 2 months ago from Priest River, ID Author

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.

jrock 2 months 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..

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dlarson 2 months ago from Priest River, ID Author

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

jrock 2 months 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

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dlarson 2 months ago from Priest River, ID Author

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!

jrock 2 months 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

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dlarson 2 months ago from Priest River, ID Author

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.

jrock 2 months 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??

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dlarson 3 months ago from Priest River, ID Author


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.

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Jim Cottengim 3 months ago

great info on the Unmentiontioned relay

Sam on the river 4 months 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.

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dlarson 4 months ago from Priest River, ID Author

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.

sam on the river 4 months ago

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

Zach Hutchinson 5 months 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

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dlarson 14 months ago from Priest River, ID Author

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.

william 14 months 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

shannon 15 months 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!

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dlarson 15 months ago from Priest River, ID Author

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.

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dlarson 15 months ago from Priest River, ID Author

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.

shannon 15 months 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.

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dlarson 15 months ago from Priest River, ID Author

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!

shannon 15 months 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?

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dlarson 15 months ago from Priest River, ID Author

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

Francisco 15 months 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

Dasis 18 months 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?

D. Cook 21 months 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...

mark stafford 23 months 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 !

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dlarson 2 years ago from Priest River, ID Author

Good call on loss of suction!

Matt custer 2 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

Matt custer 2 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

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dlarson 2 years ago from Priest River, ID Author

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).

Matt custer 2 years ago

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

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dlarson 2 years ago from Priest River, ID Author

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.

Matt custer 2 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?

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dlarson 2 years ago from Priest River, ID Author

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).

Matt custer 2 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

Matt Custer 2 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

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dlarson 2 years ago from Priest River, ID Author

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!

Matt Custer 2 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

Mobile dlarson 2 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.

Matt custer 2 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

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dlarson 2 years ago from Priest River, ID Author

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.

Matt Custer 2 years ago

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

Matt custer 2 years ago

Thank ya for the help I'll try that

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dlarson 2 years ago from Priest River, ID Author

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.

Matt custer 2 years ago

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

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dlarson 2 years ago from Priest River, ID Author

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.

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Matt Custer 2 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?

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dlarson 2 years ago from Priest River, ID Author

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

Tony 2 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.

Jm 2 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.

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dlarson 2 years ago from Priest River, ID Author

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.

joeo4852 3 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.

Jim 3 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.

wayne 3 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.

William hill 3 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?

thanks 3 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.

Zach 3 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?

Zach 3 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?

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dlarson 3 years ago from Priest River, ID Author

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

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dlarson 3 years ago from Priest River, ID Author

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

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dlarson 3 years ago from Priest River, ID Author

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

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dlarson 3 years ago from Priest River, ID Author

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...

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dlarson 3 years ago from Priest River, ID Author

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

mark 4 years ago

Thank you Dlarson. I have a 1985 Nissan 72o. Best truck I have ever owned. Had a blown horn fuse and used the haynes repair manual as a guide. Noticed no fuses where in 5 or 9 slots. So I took out and. Next day went to start up and it acted liked was flooded. Then check for spark. Got new fuel filter which need anyway. Figured next logical step was fuel pump. Didn't hear any sound and no pause to fuel pump. Then I went on line to rearch relay and shut of relay. And ran across your article. Went out and put fuse back in 15 amp back in 5 slut and started like a charm. You gave me a lot of money and a lot of grieve. I salute you sir.

Larry 4 years ago

Just bought my 1985 720 4x4 a couple of weeks ago. When it failed to start, I started looking online for a fuel system schematic. Your article was the first one I looked at. Jumped out the relay and fuel pump ran! New relay ordered. Thanks!!!

Rocky 4 years ago

Never could figure out what was wrong with my 85 720 z24, sometimes it would run sometimes it wouldn't so I have been letting it sit for quite a while. I tried to start it and the same old starved for fuel scenario. I jumper wired it and presto. This had baffled me for YEARS. I may even try to just solder the relay now rather than replace. Either way I have to go, a BIG thank you for taking your time to share this information.

nick - '84 720 4 years ago

Worked like a charm - brilliant - thank you

Jonathan Dente 4 years ago

I just got the 1984 nissan/datsun 4x4. Have owned it for 2 weeks and it dies every couple days, then will sometimes start in 10 minutes, sometimes i have to put gas in the carb to get feul in the system then it dies a couple days later. Sounds like you figured out my problem. I will get the new relay and once installed I will re-post with a follow up. Thank you for taking the time to put this information together and make it available. Even though the problem is current in my truck, 2 days ago i ran it 300 miles down into Baja to surf and really enjoyed this old truck, light, smooth running and 4x4 all at 30mpg.

jose 4 years ago

i had the same problem w/ my p/u truck, and i just find the relay,,, so i'm on my way to the auto parts,,, i hope they have this one,,,i'm in MEXICO SO WISH ME LUCK AND THANKS FOR YOUR TIME,,I'M SURE LOT OF PEOPLE WILL THANK YOU FOR THIS,,,THANK'S AGAIN

len 4 years ago

relay acts - voltage from alternator and no oil pressure - not power to fuel pump

Hope mine doesn't quite again.

Rick 5 years ago

Mine has died a few times while out on loggin roads and once in town. All times if I let it sit for 10 minutes to a half hour it fires up again. The strange thing is that when this happens I can hear my fuel pump running, and it still is not getting fuel (verified). SO today I saw this site and messed with the relay and found the strangest thing. I actually unplugged my relay, I heard it stop, then started the truck and let it run for 10 minutes. It never died even with the fuel pump off. Weird huh..

Kenora Boy 5 years ago

Bought my '85 Nissan King cab a year ago and loved it until it started to just die on the side of the road. Punched in key words on Google and lucky for me... I found your post! I had not spent a lot of $$ on the issue as I had ruled out all the main issues and wasn't sure if it was worth going farther. Found the part on-line and just installed it the other day. So far so good. Thanks for taking the time to make your post. The world is a better place when we all work together.

GBar 5 years ago

Just prior to tackling re-plumbing/re-wiring the fuel

pump& replacing all the old hoses and external fuel filter on my friend's '84 2.4l p/u, I used that 'empty'

slot (fuse #5) to replace one I'd blown (#2, I believe.)

My friend had discovered your site, and one minute after

logging on, popping a 10A into slot #5 had the truck purring.

Would I have thought to try this if you hadn't included 'Repair Manual Discrepancies?' I think so, eventually, as maxim #1 for me is "ALWAYS LOOK at whatever you messed with last or recently BEFORE you start throwing parts." Keeping notes helps...

I categorically wouldn't have fixed it in ONE MINUTE, though. Maybe several hours. Thanks so much!

Manuals 5 years ago

Very informative. Keep up the good works...

danibuggy 5 years ago

Thank you for the hint! small hands really helps...

Thanks again I discovered that the solder was not broken and I had to go one step further I cleaned the relay contact inside the clear case what a pain but the rig is back to going strong!

diesel mechanic 5 years ago

washed engine off at car wash,throttle goes wide open above 2000 rpm ?

diesel mechanic 5 years ago

what are the six wires going to the carb. for

Ed 5 years ago

Great article, I figured this one out about two years ago by accident. I have two 720s that had the same problem. They are now running well. Problem now is my truck starts up and runs ok until I put it in gear and then it stops (automatic) however if I let it warm up for a few minutes, sit runs ok...what's going on....?

Wayne Caverly 5 years ago

any way i can get a photo posted of the resisters have one that is fried and cant see the color code.

aaron 5 years ago

thank you so much all this detail that you gave helped me.. my truck runs great now.. thank you

ncpdx 5 years ago

Thank you so much for your detailed information that resolved the issue with my 1985 Nissan pickup. The fuel pump had been changed twice within a year and I knew it couldn't possibly need another fuel pump. You saved me a lot of money and time with your thorough diagnosis. Bless you!

dlarson profile image

dlarson 5 years ago from Priest River, ID Author

Sergio: The relay should be under the kick panel on the passenger side wall, next to and slightly above the heater blower.

Quintin: I believe it's purpose is exactly as you say. It may also help prevent flooding the carburetor. I recently had some trouble when my alternator failed - which also shut down the fuel. My best guess is that the shutoff is intended prevent fuel from continuing to pump out of a possibly broken fuel line and maybe feeding a nasty post-accident fire.

Quintin 5 years ago

I've had issue with this tiny box for sometime. What is it's actual complex purpose? For now, I've simply jumped accessory to fuel pump. Key on, pump on-key off, pump off. If the truck rolls over and loses oil pressure, I've probably got larger problems than fuel spillage....

Acurrate assumption?

sergio 5 years ago

ok.. i found the auto choke relay but i don't see the relay your talkin about.. does my truck not have one.?

i have this problem but no fuel relay nothing..??

Paul Madigan 5 years ago

Thank you. My 84 720 2.0 exhibited the symptoms outlined above- intermittent stalling. My mechanic spent about an hour and a half and discovered the problem - fuel pump relay. Right! It is mentioned nowhere in the manual as you correctly pointed out.

We did not fix it that day and he has since moved away. With this article, I will fix it myself (or replace it if O'Reilly can get me one). Again many thanks for the article and pictures.

Billy 5 years ago

Very helpful exactly what the problem was with my 85 nissan

Ray 6 years ago

Thanks for posting this info. This solves my truck problems when the truck would stall unexpected while driving after hitting some potholes on the road. The car would sputter like it was running out of gas and quits and then won't start for a few minutes. I was going crazy trying to figure it out. I had a clue when I heard that fuel pump relay chattering occasionally and sometimes my oil pressure gauge stopped working (since it was related to the same relay). I found out later that my friend who owns the same 4x4 pickup had the same problem and he always carries a spare relay with him.

juanito 6 years ago

es muy bueno

Mac 6 years ago

Would like to Thank You for your Posting of this Information, "ran out of fuel the otherday, truck ran great til I put $20 in tank, Now it will run for 4-5 blocks then die" someone had suggested relay but I to could not find it in the Haynes/Chilton. Thanks again for your assistance. Mac "from The GREAT NORH WEST"

Stephanie 6 years ago

Dlarson thank you so much for your article. We replaced fuel pump, fuel line, coils, fuel filter and spark plugs with no luck and were at the end of our rope until I came across your article. We found the black box, resoddered the board and so far so good. Thanks again!

Chris 6 years ago

Thank you immensely for posting this. I have been trying to chase down this problem for over a year now. I replaced the fuel pump, the relay, and still no juice to the fuel pump unless I run it constant hot. I have asked and asked about a diagram for the wiring coming into and out of the relay with no help, finally. Again thank you, and you can get the relays at O'reilly's fairly cheap. I paid $20 and change.

Shannon Paulk 6 years ago

Nice hub. I'll keep this one in mind next time I refer to Haynes.

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