emunder Posted June 15 Share Posted June 15 Figured I'd ask the guru's. My truck is an 86' w/ the 300 I6. I have a single 19 gallon gas tank. Just replaced the sending unit and tank to match what was in there. Fuel gauge still does not work correctly. My fuel pump is electric and mounted on the sending unit in the tank. In looking at my block there is no hole for a mechanical fuel pump. Also...my wiring harness that connects to the sending unit is also 4-prong so from what I can tell it came with an electric fuel pump from the factory. The other style sending units I see without the electric fuel pump are only 2-prong. I was thinking...was this truck possibly fuel injected originally? I though fuel injection for the 300 didn't come until 1987. In 86' they only offered it on the 302? When I bought the truck it had the single barrel feedback YFA carb and someone added an aftermarket fuel pressure regulator. I was under the impression that they used a manual fuel pump with a carb. I pulled all the emmissions and did the DSII swap with a vacuum dizzy and non-feedback carter. Truck runs great, just trying to figure out what came stock so I can get the correct sending unit so my gas guage works. If the one I have is correct then I need to figure out why it's not working correctly. I've read on here that sometimes they are just bad, even if new but they cost about $50 so I don't want to keep playing this game lol. Any advice would surely be appreciated so I can get this sorted out. Thanks! Link to comment Share on other sites More sharing options...
85lebaront2 Posted June 15 Share Posted June 15 Look at your VIN, 8th character is the engine. Gary should have a list. There is also a possibility that if that is not the original engine, it is a newer one that has been set up to run in your truck. Link to comment Share on other sites More sharing options...
Gary Lewis Posted June 15 Share Posted June 15 Look at your VIN, 8th character is the engine. Gary should have a list. There is also a possibility that if that is not the original engine, it is a newer one that has been set up to run in your truck. The engine codes are, oddly enough, at Documentation/Specifications/Engine Codes. I agree that, from everything I've seen, the only EFI'd engine in 86 was the 302. And the 300's had a mechanical fuel pump. So this sounds like something that was swapped in. But then why use a feedback carb? Link to comment Share on other sites More sharing options...
emunder Posted June 15 Author Share Posted June 15 The engine codes are, oddly enough, at Documentation/Specifications/Engine Codes. I agree that, from everything I've seen, the only EFI'd engine in 86 was the 302. And the 300's had a mechanical fuel pump. So this sounds like something that was swapped in. But then why use a feedback carb? I appreciate the feedback. Definitely a 300 from the factory per the Marti report. Wonder if they swapped the engine out with another 300 block from 87 and up. Weird no doubt. Link to comment Share on other sites More sharing options...
FuzzFace2 Posted June 16 Share Posted June 16 I appreciate the feedback. Definitely a 300 from the factory per the Marti report. Wonder if they swapped the engine out with another 300 block from 87 and up. Weird no doubt. That is a strange one and not even close to the Sept. cut over date for new models If you did not buy the truck new anything could be with the motor but as a guess it was changed for a newer but .......... You say the sender plug has 4 wires, 2 for sender and 2 for the pump. This wiring if you follow it back no splicing, looks factory? If it is a factory electric pump I would think there would be a factory relay under the hood like the factory electric pump trucks. On the gauge what testing have you done? With a test light you need to see what wires do what. Fuel pump should be hot all the time and the sender will blink. I would think the other 2 are grounds but test them too. If you do have a blinking wire that is good. Ground that wire and with the key on the gauge should go to full. Do not do this to long as you can hurt the gauge. This test the wire from sender to the gauge and the gauge. If no blinking or gauge moves when grounded more testing is needed. Dave ---- Link to comment Share on other sites More sharing options...
emunder Posted June 19 Author Share Posted June 19 That is a strange one and not even close to the Sept. cut over date for new models If you did not buy the truck new anything could be with the motor but as a guess it was changed for a newer but .......... You say the sender plug has 4 wires, 2 for sender and 2 for the pump. This wiring if you follow it back no splicing, looks factory? If it is a factory electric pump I would think there would be a factory relay under the hood like the factory electric pump trucks. On the gauge what testing have you done? With a test light you need to see what wires do what. Fuel pump should be hot all the time and the sender will blink. I would think the other 2 are grounds but test them too. If you do have a blinking wire that is good. Ground that wire and with the key on the gauge should go to full. Do not do this to long as you can hurt the gauge. This test the wire from sender to the gauge and the gauge. If no blinking or gauge moves when grounded more testing is needed. Dave ---- Correct...it does have the 4 wire plug. I'll check to see if maybe they spliced a newer plug in. I'll also check to see if there is a relay. I have not tested the sending unit yet. I bought a new one and figured that would do the trick so I'll have to check into this. Thanks for all the information! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 23 Share Posted June 23 Correct...it does have the 4 wire plug. I'll check to see if maybe they spliced a newer plug in. I'll also check to see if there is a relay. I have not tested the sending unit yet. I bought a new one and figured that would do the trick so I'll have to check into this. Thanks for all the information! Look in the EVTM for 1986, under fuel selector & gauges -section 18- you see the single tank option in the 1st diagram No relays, no switch valve to fail. BUT the ground travels all the way back to G701, at the right of the radio. https://www.garysgaragemahal.com/fuel-tank-selector--gauges1.html Grounds are shown in the front of the manual... Link to comment Share on other sites More sharing options...
85lebaront2 Posted June 23 Share Posted June 23 Look in the EVTM for 1986, under fuel selector & gauges -section 18- you see the single tank option in the 1st diagram No relays, no switch valve to fail. BUT the ground travels all the way back to G701, at the right of the radio. https://www.garysgaragemahal.com/fuel-tank-selector--gauges1.html Grounds are shown in the front of the manual... Jim, I haven't found what Ford's electrical desiners were on when these were designed, but it must have been some good stuff. In the words of Cheech and Chong, "dynomite sheet mon". Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 23 Share Posted June 23 Jim, I haven't found what Ford's electrical desiners were on when these were designed, but it must have been some good stuff. In the words of Cheech and Chong, "dynomite sheet mon". The system (circuit) seems perfectly normal to me?.?.?. I imagine that I might incorporate a ground near -but not AT- the fuel tank. Of course this would introduce a new place for corrosion to get a foothold.... 701 is ground zero. These trucks were superseded by '88, and never intended to last more than a decade. I'm sure engineering spent way too much time to meet mandates for crash & fire safety and the like. They were also tied up with frivolous things like David's aero package, trying to squeeze a single mpg out of a barn door. Link to comment Share on other sites More sharing options...
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