The Datsun and Nissan Pickup Fuel Pump Relay - What the Haynes© Automotive Repair Manual Won’t Tell You
83Who This Pertains To
This article is written 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 (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 – 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 a fuel pump relay – or 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!
Where Is It and How Do I Get It Out
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 to it – 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
Eliminate Less Expensive Repairs First
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
Repair It or Replace It?
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!
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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.
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!
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"
es muy bueno
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.
Very helpful exactly what the problem was with my 85 nissan
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.
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..??
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: 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.
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!
thank you so much all this detail that you gave helped me.. my truck runs great now.. thank you
any way i can get a photo posted of the resisters have one that is fried and cant see the color code.
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....?
what are the six wires going to the carb. for
washed engine off at car wash,throttle goes wide open above 2000 rpm ?
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!
Very informative. Keep up the good works...
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!
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.
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..
relay acts - voltage from alternator and no oil pressure - not power to fuel pump
Hope mine doesn't quite again.
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
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.
Shannon Paulk 2 years ago
Nice hub. I'll keep this one in mind next time I refer to Haynes.