sgauvry Posted March 23, 2018 Share Posted March 23, 2018 To those of you that have been providing advice and following the build of my 1985.5 F150 5.0, I'm almost there with regard to having a working engine. Remaining to be done is to drill a hole in my exhaust for a new O2 sensor that I want to move further downstream to ensure I'm getting exhaust from both headers, and weld in a bung. And, I am waiting for one more air filter to arrive to complete my intake system. That should be it, barring any major issues. Speaking of issues - I was expecting a few with regard to the electrical system but nothing that a tweak here and there would not cure. Today, an issue popped up. I cranked the engine to see what kind of fuel pressure I'm getting. I can hear the rail HP pump engage for a split second, as it is supposed to. I do not believe my in-tank sending unit is supplying fuel. The fuel gauge remains unchanged when cranking the engine. The first thing I'll check is to see that the tank unit is getting power. If not, I'll have to do some checking to see where there's a break in the circuit. This is a single tank operation, so there's no tank selector that I'm aware of. I'll also attempt to check relays to ensure they are working as they should. This is where I need to advice. How do I go about checking relays to ensure they are opening and closing? Off to the dentist for now but will resume work on my truck when I return. I'll take any advice you have to offer with regard to the fuel system. Thanks!! Steve Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 23, 2018 Share Posted March 23, 2018 Steve - Page 103 (http://www.garysgaragemahal.com/electric-fuel-pump-control.html) shows the circuit. And you only have one relay. You can check for power out of it on the pink/black wire, which goes back to the in-tank pump as well as the in-line pump. Link to comment Share on other sites More sharing options...
sgauvry Posted March 23, 2018 Author Share Posted March 23, 2018 Steve - Page 103 (http://www.garysgaragemahal.com/electric-fuel-pump-control.html) shows the circuit. And you only have one relay. You can check for power out of it on the pink/black wire, which goes back to the in-tank pump as well as the in-line pump. Thanks, Gary! Saw that earlier, but I appreciate the feedback. I'll let you know how make out. Probably get to it tomorrow. Link to comment Share on other sites More sharing options...
vjsimone Posted March 23, 2018 Share Posted March 23, 2018 Are you still using your 4 wire heated O2 sensor ? Link to comment Share on other sites More sharing options...
sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 Are you still using your 4 wire heated O2 sensor ? I know that until the sensor reaches about 650F it doesn't even start to generate voltage to send signal to the PCM. That causes the engine to run rich on short trips which is mostly what I do with that truck. A heated O2 is better for the engine overall to help it burn clean, improve fuel economy a bit, and to keep the O2 sensor healthy longer. I suppose that should decide it for me. I'm moving the O2 sensor further downstream so as to be certain both exhaust are incorporated. Waiting for a bung to arrive so I can do that. I won't forget to ground it with a ground strap. Presently, I'm trying to figure why my in-tank fuel pump has 0 volts coming to it. Once the sun comes up, I'm going to follow that pink/black H wire back to the external pump. I know the external pump has power, so the problem is occurring between the two. Shouldn't be too hard to figure. Sure do love that "Electrical & Vacuum Troubleshooting Manual" you provided to me. It opens a lot of doors to figuring stuff out. Otherwise it's nothing but guesswork. Link to comment Share on other sites More sharing options...
sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 Steve - Page 103 (http://www.garysgaragemahal.com/electric-fuel-pump-control.html) shows the circuit. And you only have one relay. You can check for power out of it on the pink/black wire, which goes back to the in-tank pump as well as the in-line pump. Gary - When I turn the ignition on I can briefly hear the HP fuel pump briefly engage. That seems to be working as it should. But the in-tank fuel pump has no voltage going to it. I checked this several times with my voltmeter with the positive voltmeter prong connected to the pink/black H wire terminal on the fuel pump connector, and the black voltmeter prong grounded to the frame. There's a connector downstream from the HP fuel pump in the rail; I believe it's C120. That connector has leads that go both to the tranny safety switch and to the in-tank fuel pump. I disconnected C120 and checked the voltage at the pink/black H wire terminal. I measured 4 volts. How many volts are supposed to go the the in-tank fuel pump? Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 24, 2018 Share Posted March 24, 2018 Gary - When I turn the ignition on I can briefly hear the HP fuel pump briefly engage. That seems to be working as it should. But the in-tank fuel pump has no voltage going to it. I checked this several times with my voltmeter with the positive voltmeter prong connected to the pink/black H wire terminal on the fuel pump connector, and the black voltmeter prong grounded to the frame. There's a connector downstream from the HP fuel pump in the rail; I believe it's C120. That connector has leads that go both to the tranny safety switch and to the in-tank fuel pump. I disconnected C120 and checked the voltage at the pink/black H wire terminal. I measured 4 volts. How many volts are supposed to go the the in-tank fuel pump? Steve - I'm confused. The EVTM shows connector C120 as having the fuel pump wires in it, but not the start wire going to the neutral safety switch. And it shows C121 as having the start wires going to the neutral safety switch but not the fuel pump wires. So, are you sure that the connector you found has both fuel pump (pk/bk) and start wires (r/lb) in it? But, moving on to the testing, the complicating factor here is the computer. At the bottom of Page 106 there's a description of when the computer (ECA) is to pull in the fuel pump relay. But, it doesn't really say that it will pull in the relay when the key is in Run. And I don't think it does pull in the relay until the engine is spinning. So I think what is happening is that the ECA is powering both pumps briefly when you turn the key on just to bring up pressure in the system, and then waiting until you crank the engine by turning the key to Start. If you pull the little red/light blue wire off the starter solenoid/relay you should be able to turn the key to Start w/o spinning the engine. And while the key is in Start you should have power to both pumps. If not you need to see if the relay is being pulled in, but let's try this first. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 24, 2018 Share Posted March 24, 2018 Gary - When I turn the ignition on I can briefly hear the HP fuel pump briefly engage. That seems to be working as it should. But the in-tank fuel pump has no voltage going to it. I checked this several times with my voltmeter with the positive voltmeter prong connected to the pink/black H wire terminal on the fuel pump connector, and the black voltmeter prong grounded to the frame. There's a connector downstream from the HP fuel pump in the rail; I believe it's C120. That connector has leads that go both to the tranny safety switch and to the in-tank fuel pump. I disconnected C120 and checked the voltage at the pink/black H wire terminal. I measured 4 volts. How many volts are supposed to go the the in-tank fuel pump? Steve, in tank pump on yours should get battery voltage when the relay is closed unless for some reason everything on the 1985.5 EFI system is completely different from the 1986-89 EFI pumps. My AllData shows a 1000 ohm resistance wire on the feed to the in-tank pump, which was eliminated in 1986. If you are only seeing 4 volts, the one question becomes, is this with the pump connected? If so, then one of two possibilities, bad connection, or pump is stuck from sitting. If Ford used the same pump in 1986-89 then try bypassing the resistance wire and see if will run then. Link to comment Share on other sites More sharing options...
sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 If you pull the little red/light blue wire off the starter solenoid/relay you should be able to turn the key to Start w/o spinning the engine. And while the key is in Start you should have power to both pumps. If not you need to see if the relay is being pulled in, but let's try this first. IHi Gary - Thanks for getting back to me. I did as you suggested. Connecting to the pink/bl h wire at the in-tank fuel pump with the red/blue wire disconnected at the starter solenoid and with the key in Start position I got 0 volts. Link to comment Share on other sites More sharing options...
sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 If so, then one of two possibilities, bad connection, or pump is stuck from sitting. If Ford used the same pump in 1986-89 then try bypassing the resistance wire and see if will run then. Interesting information. My fuel gauge is reading as full, but I know there;s only about 3/4 of a tank. It is possible the pump is stuck from sitting. I do not know how to bypass the resistance wire. I'll look in my manual to see which wire that is, but how do I bypass it. Link to comment Share on other sites More sharing options...
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