sTanTruck Posted April 6 Report Share Posted April 6 Hey everyone, I have been watching this forum for a while now and this is my first post! I recently bought a 1986 Nissan 720 4wd 5-speed truck to tinker with and play on some dirt roads in the area. I am having a fueling issue where the truck will run for about 5-10 minutes then sputter and die. I originally thought this was caused by a previous owner's "fix" where they jumped the fuel pump/shutoff relay to just run off the accessory power. I tried to fix the relay to no avail and ended up getting a new one. I will be installing it tomorrow but there are a few other things I need to do to as well. Replacing the fuel filter, verifying the oil switch and alternator signal to the relay, and fixing some damaged wires to the pump. What kind of signal should I expect to see from my oil switch to verify that it is working? I would assume seeing 12v after a few minutes of running would tell me that it is working correctly. Similarly, will the alternator signal give me ~12v while the truck is running? Any other advice for what could be causing this fueling issue would be much appreciated. Thank you, Dylan Quote Link to comment
datzenmike Posted April 6 Report Share Posted April 6 If it has the jumper them the fuel pump should be working with the ignition on. Turn ignition on and go back to the pump just forward of the right rear tire. Is it running? Best to try the new pump relay first as it may resolve any and all problems. 1/ As to the question about the oil pressure switch, it is grounded when oil pressure drops below around 8 PSI and this draws power through the red oil light in the dash turning it on as a warning. This ground is also fed to the pump relay and is a good indication the engine has shut off. 2/ If the alternator should stop charging the red charge warning lamp is grounded by the diodes in the alternator and this turns it on. This ground is also fed to the pump relay. The no charge condition is a good indication that the engine has shut off. If 1/ and 2/ are at ground then the pump shuts off. In an accident you don't want the fuel pump running obviously. 1 Quote Link to comment
sTanTruck Posted April 7 Author Report Share Posted April 7 The fuel pump would run interminably. When it sputtered and died the last time even when I jumped it straight to 12v I couldn't get the fuel pump to come on. I just changed the fuel filter, and put the new relay in. The pump came on once, then when I went to start it the relay started making a really awful noise. Here is the link to the video: hhttps://youtube.com/shorts/y2AQ3vb192A?si=1w6QvXHkxAwkCS_n Have you heard this before? I am going to unhook the oil switch wire and the alternator wire next to see if those are causing any issues. Thank you for your quick response! Quote Link to comment
sTanTruck Posted April 7 Author Report Share Posted April 7 Update: I was trying to disconnect the oil switch and accidentally twisted the wire off 😞 BUT the pump now runs flawlessly ( and the old relay wasn't actually bad!). So I am now going to put the new relay in and order a new oil switch. Any suggestions on how to remove this switch? I have heard it can be a pain to get to Quote Link to comment
datzenmike Posted April 7 Report Share Posted April 7 You need a non metric 9/16" or 5/8"??? I don't think 14mm fits and 15mm is too large. It's a BSPT fitting. Also the spanner is best if thin to slip down in behind the sender. What ever you do, resist the urge to just grab the outer case and twist it. 1 Quote Link to comment
Thomas Perkins Posted April 7 Report Share Posted April 7 (edited) Remove the oil filter.Get one with a lifetime warranty.I got mine from Orielly"s.I had to modify the fittings cause mine dry rotted long ago.I use the one with the gauge,cost more than the one with light. Edited April 7 by Thomas Perkins 1 Quote Link to comment
sTanTruck Posted April 10 Author Report Share Posted April 10 I also am having difficulty determining if my thermostat is bad or if my gauge is reading incorrectly for the water temp. I drive the truck for 45 minutes on the highway at about 65F and the gauge for water temp is only reading just above the lowest tick mark. It does seem to change which makes me think my gauge could be working and my thermostat is stuck open. Any suggestions on how to check this without pulling the thermostat out? Or at least narrow it down to the gauge or thermostat? I am still waiting on a gasket but I am planning to put a 180F thermostat in it. Quote Link to comment
datzenmike Posted April 11 Report Share Posted April 11 Borrow an IR (infrared) gun and shoot the top of the thermostat cover when warmed up. Should be over 180F. Thermostats don't last forever, it's probably stuck open. Thermostats set the minimum engine temperature. Think about that. If they are working they don't cause over heating they prevent over cooling. When I got my '74 710 the gauge barely read. I don't waste time when there is any question about the cooling system, I immediately replace the thermostat. Here's the original thermostat... 1 Quote Link to comment
sTanTruck Posted April 11 Author Report Share Posted April 11 Thats a good way to think about it (thermostats set the minimum temp). I saw one of your replies to a different thread saying to ground the water temp sensor wire to verify the gauge is working properly. When I did this the temp read full hot so my gauge is working and reading accurately. Parts are on the way and I will update this thread when I install the new thermostat. Also, I did the same trick to my fuel gauge by shorting the sending unit wires and watched the tank read full. Cleaned up the connections and now I have a working fuel gauge without having to drop the tank!! Where are you guys sourcing rubber replacements? I need new door seals (inner and outer) and the selection on RockAuto is limited to windshield and rear window seals (which I plan on replacing once it stops raining constantly here). I also need to find the piece where the cigarette lighter mounts because I broke mine trying to get it out. The salvage yards here are slim pickings on trucks like this. Thank you for your help! Quote Link to comment
sTanTruck Posted April 11 Author Report Share Posted April 11 Another question: Is there an O ring or seal that will go around the thermostat? The one I ordered did not say if it came with one and I don't want to find out once I have removed it from the truck. Quote Link to comment
datzenmike Posted April 12 Report Share Posted April 12 The thermostat housing has a slight recess the thermostat sits down into and a paper gasket goes on top to seal. That's all you need. Probably the gaskets are still available. You can use the top cover to trace out your own gasket using scissors and a dollar store hole punch.. This is boughten gasket material but my oil pump, water pump and the thermostat gaskets are made from Cheerio's box When installing the thermostat place with the juggle valve to the top. If it has one... 1 Quote Link to comment
sTanTruck Posted April 12 Author Report Share Posted April 12 The paper wont degrade when exposed to coolant? Im all about a cheap DIY solution! Also good point about the jiggle valve, I never knew that and Im glad I don't have to learn that the hard way! Quote Link to comment
sTanTruck Posted April 12 Author Report Share Posted April 12 Where is the best place to find rubber door seals? Quote Link to comment
datzenmike Posted April 12 Report Share Posted April 12 E-Bay? best?? ... I don't know. Quote Link to comment
datzenmike Posted April 12 Report Share Posted April 12 7 minutes ago, sTanTruck said: The paper wont degrade when exposed to coolant? Im all about a cheap DIY solution! Also good point about the jiggle valve, I never knew that and Im glad I don't have to learn that the hard way! It's cardboard and they've been on there for 10 years. Quote Link to comment
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