85lebaront2 Posted March 31, 2020 Share Posted March 31, 2020 Good point, Bill. I've included the '86 schematic below. It'll be interesting to see how his is wired. As for the filter, I'm not sure that is it as he ran a jumper to the pump and that solved the problem. But, do you think that by bypassing the resistor in the wiring that could do it with a dirty filter? The difference is in the tank selector valve, all 1985/86 EFI trucks I have seen had the big reservoir tank selector valve. The only resistors were on the in-tank pump carbureted trucks (460 w/hot fuel handling package). If he hot wired both sides of the system (power and ground) and it works, I would look at G701 as the entire system grounds there. Link to comment Share on other sites More sharing options...
Greg 85 Posted April 1, 2020 Author Share Posted April 1, 2020 Good point, Bill. I've included the '86 schematic below. It'll be interesting to see how his is wired. As for the filter, I'm not sure that is it as he ran a jumper to the pump and that solved the problem. But, do you think that by bypassing the resistor in the wiring that could do it with a dirty filter? I believe mine is the latter due to the fuel pump cutout relay. Hopefully it will dry out enough today for me to crawl under it and start searching for the issue. Link to comment Share on other sites More sharing options...
Greg 85 Posted April 1, 2020 Author Share Posted April 1, 2020 The difference is in the tank selector valve, all 1985/86 EFI trucks I have seen had the big reservoir tank selector valve. The only resistors were on the in-tank pump carbureted trucks (460 w/hot fuel handling package). If he hot wired both sides of the system (power and ground) and it works, I would look at G701 as the entire system grounds there. I am trying to figure out the^^^^ "big reservoir tank selector valve" as I have a fuel filter housing with the big tank and filter, but if memory serves I believe my selector valve is seperate? Am I following that correctly? Link to comment Share on other sites More sharing options...
Greg 85 Posted April 1, 2020 Author Share Posted April 1, 2020 It is actually a dual tank set up and I had completely bypassed the factory wiring and hooked up directly to the battery with a toggle switch for testing purposes. Allow me to clearify this, I only bypassed the high pressure pump, the rest of the system was connected to the factory harness and was working as it should. I had fuel to the HP pump but the HP pump wasn't engaging to build the pressure. So I disconnected the HP pump power and ground and connected power and ground by the battery through a toggle and had no issues. Ran good. So I will need to trace out the wiring for the HP pump and find the power loss. Right? Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 1, 2020 Share Posted April 1, 2020 It is actually a dual tank set up and I had completely bypassed the factory wiring and hooked up directly to the battery with a toggle switch for testing purposes. Allow me to clearify this, I only bypassed the high pressure pump, the rest of the system was connected to the factory harness and was working as it should. I had fuel to the HP pump but the HP pump wasn't engaging to build the pressure. So I disconnected the HP pump power and ground and connected power and ground by the battery through a toggle and had no issues. Ran good. So I will need to trace out the wiring for the HP pump and find the power loss. Right? Yes, you need to follow the wiring and find out where the power stops. And to clarify, if you have the wiring shown in the '86 EVTM then there is no resistor. So disregard what I said about that. Further, that diagram doesn't show the switch built into the unit on the frame. Just the switch on the dash. So it is less complex and should be easier to resolve. Link to comment Share on other sites More sharing options...
85lebaront2 Posted April 1, 2020 Share Posted April 1, 2020 The difference is in the tank selector valve, all 1985/86 EFI trucks I have seen had the big reservoir tank selector valve. The only resistors were on the in-tank pump carbureted trucks (460 w/hot fuel handling package). If he hot wired both sides of the system (power and ground) and it works, I would look at G701 as the entire system grounds there. I am trying to figure out the^^^^ "big reservoir tank selector valve" as I have a fuel filter housing with the big tank and filter, but if memory serves I believe my selector valve is seperate? Am I following that correctly? Greg, if the filter/tank unit has 6 ports (3 large and 3 smaller ones) they should be plumbed with one large port to the HP pump, and the adjacent smaller port to the fuel return on the engine fuel rail. The primary filter should be in front of the HP pump. The top portion of that assembly is a diaphragm operated tank selector valve. Whichever in-tank pump is active moves the in-feed to the reservoir to that port and opens the corresponding return line to that tank. The other 4 ports will be: 1 large and one smaller to the front tank and 1 large and one smaller to the rear tank. If the in-tank pumps are working then the power/ground factory wiring is good to that point. Your issue would probably be in connector C127 at the pink with black dash? wire. The fuel tank selector is on the "upstream" side of that so power is good to there, the ground side should also be good due to the way the system is wired. Any breaks in the portion of the harness to the HP pump on either side, power or ground will prevent it from running. Link to comment Share on other sites More sharing options...
Greg 85 Posted April 2, 2020 Author Share Posted April 2, 2020 Greg, if the filter/tank unit has 6 ports (3 large and 3 smaller ones) they should be plumbed with one large port to the HP pump, and the adjacent smaller port to the fuel return on the engine fuel rail. The primary filter should be in front of the HP pump. The top portion of that assembly is a diaphragm operated tank selector valve. Whichever in-tank pump is active moves the in-feed to the reservoir to that port and opens the corresponding return line to that tank. The other 4 ports will be: 1 large and one smaller to the front tank and 1 large and one smaller to the rear tank. If the in-tank pumps are working then the power/ground factory wiring is good to that point. Your issue would probably be in connector C127 at the pink with black dash? wire. The fuel tank selector is on the "upstream" side of that so power is good to there, the ground side should also be good due to the way the system is wired. Any breaks in the portion of the harness to the HP pump on either side, power or ground will prevent it from running. I hooked everything back up as it should be, tried to start, started ran decent for thirty minutes, surging up and down but running. Test drove to gas station. Turned off, fueled, started back up with no issue other than the surging. Let run a few minutes and then put it in gear and it died, wouldn't restart. Popped the hood, wiggled wires, crawled underneath wiggled wires, tried to start c.n.s. waited about 15 minutes and tried again, acted like it wanted to. Tried again, started still surging, drove home. Once home popped the hood while running and wiggled wires up top and bottom no issues, sat down by the truck with a glass of sweet tea going through the schematic and it just died out of nowhere. Continuing to trace wires unless you think that I am barking up the wrong tree. Thoughts? Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 2, 2020 Share Posted April 2, 2020 Greg, if the filter/tank unit has 6 ports (3 large and 3 smaller ones) they should be plumbed with one large port to the HP pump, and the adjacent smaller port to the fuel return on the engine fuel rail. The primary filter should be in front of the HP pump. The top portion of that assembly is a diaphragm operated tank selector valve. Whichever in-tank pump is active moves the in-feed to the reservoir to that port and opens the corresponding return line to that tank. The other 4 ports will be: 1 large and one smaller to the front tank and 1 large and one smaller to the rear tank. If the in-tank pumps are working then the power/ground factory wiring is good to that point. Your issue would probably be in connector C127 at the pink with black dash? wire. The fuel tank selector is on the "upstream" side of that so power is good to there, the ground side should also be good due to the way the system is wired. Any breaks in the portion of the harness to the HP pump on either side, power or ground will prevent it from running. I hooked everything back up as it should be, tried to start, started ran decent for thirty minutes, surging up and down but running. Test drove to gas station. Turned off, fueled, started back up with no issue other than the surging. Let run a few minutes and then put it in gear and it died, wouldn't restart. Popped the hood, wiggled wires, crawled underneath wiggled wires, tried to start c.n.s. waited about 15 minutes and tried again, acted like it wanted to. Tried again, started still surging, drove home. Once home popped the hood while running and wiggled wires up top and bottom no issues, sat down by the truck with a glass of sweet tea going through the schematic and it just died out of nowhere. Continuing to trace wires unless you think that I am barking up the wrong tree. Thoughts? Have you checked the fuel pressure? I think that's where I'd start. That's because an electrical issue should be binary - on or off. But you have fluctuating symptoms. So I'd look elsewhere. And, what about pulling codes? Link to comment Share on other sites More sharing options...
Greg 85 Posted April 3, 2020 Author Share Posted April 3, 2020 Have you checked the fuel pressure? I think that's where I'd start. That's because an electrical issue should be binary - on or off. But you have fluctuating symptoms. So I'd look elsewhere. And, what about pulling codes? Okay, so I would check fuel pressure but I cannot find a schraider valve/ port to connect to. I have looked up and down the rail, in the front and back and cannot find one. Is it hidden? Also, I have a scanner but it is for obd2, isn't an '85 a obd1? Should I purchase a scanner for obd1? I have not seen a CEL on but that doesn't mean the bulb aint blown and its full of codes. Do you think it is possible that I have a ignition module or coil breaking down when it gets to running temp? This was my next move prior to your response. Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 3, 2020 Share Posted April 3, 2020 Have you checked the fuel pressure? I think that's where I'd start. That's because an electrical issue should be binary - on or off. But you have fluctuating symptoms. So I'd look elsewhere. And, what about pulling codes? Okay, so I would check fuel pressure but I cannot find a schraider valve/ port to connect to. I have looked up and down the rail, in the front and back and cannot find one. Is it hidden? Also, I have a scanner but it is for obd2, isn't an '85 a obd1? Should I purchase a scanner for obd1? I have not seen a CEL on but that doesn't mean the bulb aint blown and its full of codes. Do you think it is possible that I have a ignition module or coil breaking down when it gets to running temp? This was my next move prior to your response. Some of the early EFI rails didn't have a schrader valve, so that may be what you have. To pull codes you don't need a reader. Go to Documentation/Electrical/Electronic Engine Controls (EEC) and then the tab for EEC-IV and the Checking Codes tab. But, you could be right about a component breaking down. However, anything that would do that would likely be in the ignition system. Have you checked for spark when it runs poorly or doesn't run? Link to comment Share on other sites More sharing options...
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