slemers Posted August 6, 2013 Report Share Posted August 6, 2013 Where the hell is the fuel pump relay on my 82 720? I found the small cube type relay under the passenger side dash but can't locate the Jidecho relay that is mentioned on numerous threads here on Ratsun.( I unplugged this relay and the pump still runs with the ign on) The truck has died a couple of times lin the last couple of days and I think it's heat related. I'm running a Weber with the stock return lines.Would it help to enlarge the return line fitting for better flow? When the truck dies the fuel pump will not run until I wait 10-15 minutes. Then when you turn on the ignition, you can hear the pump run and the truck starts I've been using it as a truck the last few weeks and don't want to get stranded somewhere in the middle of an intersection. Slemers. 1 Quote Link to comment
Tinman Posted August 6, 2013 Report Share Posted August 6, 2013 It's tucked waaay up there on the right, generally above the cube relay. It's a pain to get to. If you manage to get the damn thing out, open it up and see if it has cracks around the relay and connector. Usually re-soldering it fixes it for good. 1 Quote Link to comment
Jdm720 Posted August 6, 2013 Report Share Posted August 6, 2013 What he said^^ It's a little higher up there. Some of us can get to it easier than others, but it's still a tight space. A stubby phillips will work. Even better, you can use a 10mm on a ratchet if you have those types of screws holding it in. (At the moment I don't remember whether they're round-head screws or hex-head) It'll be easier to unplug once you have it hanging. 1 Quote Link to comment
datzenmike Posted August 6, 2013 Report Share Posted August 6, 2013 Read this.... http://dlarson.hubpages.com/hub/The-Datsun-and-Nissan-Pickup-Fuel-Pump-Relay-What-the-Haynes-Automotive-Repair-Manual-Wont-Tell-You FP Relay 1 Quote Link to comment
datzenmike Posted August 7, 2013 Report Share Posted August 7, 2013 Shutting off for 10 min could be the electric pump over heating. Check the filter in the twist off bottom and if there is another in line between it and the tank. Do not enlarge the restriction in the return line. The restriction is what allows the pump to build up 3 PSI of pressure so it can push it's way into the carb. Without it gas will simply take the easiest route..... back to the tank. 1 Quote Link to comment
slemers Posted August 7, 2013 Author Report Share Posted August 7, 2013 Thanks, I'll stick my head under the dash again and let you know what I find. I pulled the shelf and the trim panel on the RH side and didn't see anything. Could it be hiding behind the blower motor? I'll check the filter in the bottom of the pump right now and see what it looks like. I used to have an airlplane that had this type of filter on the pump. Slemers 1 Quote Link to comment
datzenmike Posted August 7, 2013 Report Share Posted August 7, 2013 On the pass side just above the kick panel you'll see small square relay probably blue or brown. This is the auto choke relay and if you have an automatic there will be a second one, an inhibit relay beside it. Look just above this relay for the fuel pump relay. It's up under the side of the dash not near the heater blower fan. 1 Quote Link to comment
slemers Posted August 7, 2013 Author Report Share Posted August 7, 2013 Thanks for the reply, Above the auto choke relay I can see where there *used* to be a mounting bracket. There are two holes where the fuel pump relay used to be(or should be) but no wiring, connector or anything else for that matter. Strange. I'm thinking somewhere along the line someone butchered the harness and did who knows what with the relay. When I pull the ignition control fuse the pump will not operate. With the key in accessory the pump does not run.I found that the ground to the fuel pump was disconnected and hooked that back up, but I don't think that has any bearing on this problem. I think you may be correct in your thinking that it could be the pump itself overheating. I don't want to throw money at this thing, I guess I can check the output of the electric pump. It sounds weak, when I turn the turn the key to the on position, I can hear the pump running. When the truck quits and I let it cool off, the pump runs but I can barely hear it. Not too scientific I know.... Slemers 1 Quote Link to comment
Tinman Posted August 7, 2013 Report Share Posted August 7, 2013 I'd go with changing both fuel filters before the pump. My pump was very quiet and somehow strained. I changed the filter in the pump itself, but it was OK. Then changed the filter from the tank.... Well, a trickle came out until I popped off the hose from the tank side..... After which I learned a valuable lesson..... Do NOT do this with a FULL tank!!! LOL!!! Gas came gushing out! New filter in place, I can now plainly hear a strong beating of the pump when I turn on the ignition. Truck starts faster, since it primes the carb almost instantly now. Someone probably removed the relay and just jumped the pump to the ignition on your truck to always run. 1 Quote Link to comment
slemers Posted August 7, 2013 Author Report Share Posted August 7, 2013 It appears that my pump is an Airtex unit and not the original type pump without a filter on or in the pump. I have changed the filter after the pump. After pricing the factory pump out I can see why they went with a Airtex.The airtex is $45 at Amazon. The stock type pump is in the $185 range. It looks like this pump has been there for awhile. I will probably spend the 45 bucks and be done with it .After researching this board it sounds like that with the stock FP relay installed, the pump initially starts and runs for 5-10 seconds then shuts off if the ignition in on and the engine isn't started. My pump runs continously if the ign is in the run position. When I pull the ign control fuse it stops running so that's where it is powered from. In the acc position it doesn't run. This truck had alot of PO mods when I bought it, he wasn't to mechanically inclined so I think he had a friend that was helping him *fix* his 720. Slemers 1 Quote Link to comment
datzenmike Posted August 8, 2013 Report Share Posted August 8, 2013 It also needs oil pressure and alternator charge to keep pumping. If you were in an accident the pump won't keep pumping gas on the fire. :lol: :lol: :lol: 2 Quote Link to comment
slemers Posted August 9, 2013 Author Report Share Posted August 9, 2013 Currently it's unsafe at any speed is what you're saying? If the relay is gone so is the protection the oil pressure and alternator provide? Running without a fuel shut-off seems less than ideal :) It felt better when my head was stuck in the sand. slemers 1 Quote Link to comment
wayno Posted August 9, 2013 Report Share Posted August 9, 2013 I gotta say this, there are a lot of cars on here and the road that have aftermarket electric fuel pumps that are not wired into the wiring harness to shut off if in a wreck, I believe they came from the manufacturers that way also, ford is one, to say that it is unsafe to now have a fuel pump that don't shut off is just crap. I ran my datsun roadster with an electric fuel pump for years and I am still here. I do think you need to fix the issue of it dying when warm outside, but as for it being unsafe, well that is an opinion, and there are a lot of them out there. 2 Quote Link to comment
slemers Posted August 9, 2013 Author Report Share Posted August 9, 2013 Thanks for your insight. 1 Quote Link to comment
RatVonDude Posted March 27, 2016 Report Share Posted March 27, 2016 so can you run 720 without the relay? Im having same problem. Already changed fuel filter. Pump seems to work fine, but gas gets restricted at certain inclines and speeds. Its probably that god damn hitachi carb. 1 Quote Link to comment
datzenmike Posted March 27, 2016 Report Share Posted March 27, 2016 The poor Hitachi is 34 years old. so give it a break. They work the best on the 720 but everything wears out. Inclines and speeds would indicate high fuel demand and delivery problem. There is a fine brass screen at the carb fuel line inlet. Maybe the float is set too high? The pump has a filter too you know. Twist the bottom off and rinse it out. I heard there is a V W filter that will replace this one. Then there is the regular inline filter. Yes you can just jumper the relay so the pump is on with the ignition. 2 Quote Link to comment
RatVonDude Posted March 27, 2016 Report Share Posted March 27, 2016 Changed that cylinder filter. Auto zone actually sold it. Is there a second fuel filter? Jump relay? All about it. Had carb rebuilt by friend mechanic. I bet that the problem. Brass inlet? Set idle too low. To jump relay do I just locate that fuel pump shut off , what about all the other stuff? Oil, alternator? Can I just yank that whole component? 1 Quote Link to comment
RatVonDude Posted March 27, 2016 Report Share Posted March 27, 2016 I changed filter in fuel pump. But have yet to find just that normal white fuel filter 1 Quote Link to comment
datzenmike Posted March 27, 2016 Report Share Posted March 27, 2016 Make a jumper from White to White/Black wires. This places power from the #5 (ignition controlled) to the fuel pump. The pump will come on with the ignition switch. It will run when ever the ignition is on.... just sayin. 2 Quote Link to comment
RatVonDude Posted March 27, 2016 Report Share Posted March 27, 2016 Make a jumper from White to White/Black wires. This places power from the #5 (ignition controlled) to the fuel pump. The pump will come on with the ignition switch. It will run when ever the ignition is on.... just sayin. So just a " jumper" between wb and w wire and just leave it at that? Can I make bridge/jumper 2" away from component? 1 Quote Link to comment
Lockleaf Posted March 27, 2016 Report Share Posted March 27, 2016 Oreilly sells the regular fuel filter. 1 Quote Link to comment
RatVonDude Posted March 27, 2016 Report Share Posted March 27, 2016 Oreilly sells the regular fuel filter. I have the regular filter just having problems locating it on truck. I'll try today. 1 Quote Link to comment
datzenmike Posted March 27, 2016 Report Share Posted March 27, 2016 So just a " jumper" between wb and w wire and just leave it at that? Can I make bridge/jumper 2" away from component? Yes, however this defeats the purpose of the relay which is to shut the pump off in an accident situation. The motor stalls (eventually) and the low oil pressure and non charging alternator can no longer keep the pump running. The jumper on the relay is just a diagnostic to prove that the electric pump actually works. The FSM is vague on operation. It has a connection to the oil pressure sender and the alternator. Now why would you have this other than to tell the relay that the engine is running or not? 1 Quote Link to comment
Lockleaf Posted March 27, 2016 Report Share Posted March 27, 2016 Sorry. Misunderstood. It's pretty close to the electric fuel pump. Look up under the side of the bed in front of the rear drivers side tire. I usually access it with one hand through the wheel well. It's awkward. 2 Quote Link to comment
datzenmike Posted March 27, 2016 Report Share Posted March 27, 2016 True in Australia, otherwise right or passenger side rear wheel if not in Australia. There is a protective box to keep dirt off the pump. The filter clips onto the frame just to the rear and above the pump. Just follow the lower pump hose about 8" up to the filter. 2 Quote Link to comment
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