Ford Fuel Pump Relay Wiring Diagram For 1986 7.5l 06 Dec, 2021 Post a Comment Merritt Hi everyone. This is my first time being a member of any forum. I have searched for previous threads related to this topic and the search came back saying there was none. Here is the problem I am currently fighting. The truck is a 1990 F250 with a 7.5L/460. Cranks all day long but will not fire. (it will fire on ether with no problem). I have spark and compression and have set timing. I have check all grounds that I can find. I have battery voltage at the eec relay, in and out. I have even replaced the ecu in complete desperation. I have power at the red wire at the injector with the ignition on. If I supply a ground to the white/gray wire the injector opens and I can hear and see fuel enter the cylinder. When using a noid light I can see that the injectors are cycling (pcm sending ground) while cranking, but they are not opening. I am not getting any fuel in the cylinders. My thinking is I have a weak ground. The ground is good enough to light the noid light (it is somewhat dim when lit) but not strong enough to open the injectors. Ideas? JWC 3 Founding Member TOTM Winner Welcome. Have you measured your fuel pressure? Is it in spec? Just asking. If you suspect a bad ground you can add a good ground and see if that helps. 1970something Founding Member TOTM Winner agreed. i would be looking at fuel pressure, and a possible bad electric fuel pump, or bad ground on the fuel tank. i would also check to see if the fuel pump inertia switch has been tripped. dustybumpers Article Contributor Founding Member I agree on fuel pressure Do you have 2 tanks? What does it do on the 2nd tank? Does the fuel pump cycle when you turn on the key for 1 second? Merritt Wow-thanks for the responses. So let me answer a few of your questions: Yes I have checked fuel pressure. 40psi (spec says 35-45) Yes I have checked the inertia switch. Yes it has saddle tanks. I purchased the truck a month or so ago knowing it was a little bit of a basket case. The previous owner removed the front tank (who knows why-he even left all the fuel pump/sender wires bare and hanging) but the rear tank is still intact and has fresh fuel in it. The fuel pump will only run when I give it 12v at the fuel tank selection switch. When given power it gives me 40psi at the rail. Pressure holds after I turn off the pump. Pressure also holds when cranking indicating to me that the injectors are not opening. I can watch the fuel pressure start to drop immediatly when I supply ground to the injector and open it. I figured I would tackle the fuel pump problem later since I can get it to work by giving it power. That problem seems a little simpler (famous last words I know.) JWC-3, I have thought about adding a ground to the injector circuit. Here lies the problem (correct me if I am wrong-which is very possible ) The injector circuit is ground side operated. Injectors are given a constant 12v supply with key on. PCM gives it a timed ground signal to open/close the injector. At least this is how I understand it. Again, I could be incorrect. If this is correct I really only have one option when trying to strenthen my ground. I would have to add a ground going to the PCM. The PCM could then use the strengthened ground to send the ground signal to the injectors. From the wiring diagrams I have the PCM has 4 grounds. I have checked resistance from the PCM connector (PCM unplugged) to both a battery post ground as well as a body ground. There is less resistance from the connector to the battery post (.9-1.1 ohms) versus a body ground (2.0 ohms). Does anyone know where the ground locations are that feed the PCM? Is it attached to the body of the truck or directly to the battery? There are mutiple grounds all over to both the body and the battery, all of which I have cleaned, tightened, etc. But I am wondering if there is one I missed. Then again, it might not be a ground issue at all. I just don't know what else would be keeping my injectors from opening. Sorry for the lengthy reply. Again, thanks for all the response!! JWC 3 Founding Member TOTM Winner Correct, you can not directly ground the injectors. The ecm control s that. You said you replaced the ecm. Used? Reman? Check the wiring close. Unplugg all injectors and see if the noid light flashes brighter. You may have a shorted injector or more. Merritt The ecm/pcm is a reman. I am thinking that it is good since none of my symptoms changed when I swapped to the remanned from the old. Or in other words, my orignal pcm is fine and I wasted my money by partially "shotgunning" it as bad. I am not sure what you mean when you say to check the wiring "close." I will unplug all the injectors and see if the noid light gets any brighter. I hadn't ever heard of a shorted injector so I never thought of trying this. Good idea. Thanks again. I'll keep you posted. dustybumpers Article Contributor Founding Member Having been through this on my 90, next step for you, go over to the solenoid and tug on the fusible links The power to the fuel driver in your ECM is one of the fusible links, and I bet one blew, and the OP bypassed it JWC 3 Founding Member TOTM Winner Like Charlie is saying. Check "all" wiring closely. Expect the unexpected. .... Source: https://www.fordtruckzone.com/threads/bad-ground.665712/ Posted by: reddmemo.blogspot.com Share
Hi everyone. This is my first time being a member of any forum. I have searched for previous threads related to this topic and the search came back saying there was none. Here is the problem I am currently fighting. The truck is a 1990 F250 with a 7.5L/460. Cranks all day long but will not fire. (it will fire on ether with no problem). I have spark and compression and have set timing. I have check all grounds that I can find. I have battery voltage at the eec relay, in and out. I have even replaced the ecu in complete desperation. I have power at the red wire at the injector with the ignition on. If I supply a ground to the white/gray wire the injector opens and I can hear and see fuel enter the cylinder. When using a noid light I can see that the injectors are cycling (pcm sending ground) while cranking, but they are not opening. I am not getting any fuel in the cylinders. My thinking is I have a weak ground. The ground is good enough to light the noid light (it is somewhat dim when lit) but not strong enough to open the injectors. Ideas?
Welcome. Have you measured your fuel pressure? Is it in spec? Just asking. If you suspect a bad ground you can add a good ground and see if that helps.
agreed. i would be looking at fuel pressure, and a possible bad electric fuel pump, or bad ground on the fuel tank. i would also check to see if the fuel pump inertia switch has been tripped.
I agree on fuel pressure Do you have 2 tanks? What does it do on the 2nd tank? Does the fuel pump cycle when you turn on the key for 1 second?
Wow-thanks for the responses. So let me answer a few of your questions: Yes I have checked fuel pressure. 40psi (spec says 35-45) Yes I have checked the inertia switch. Yes it has saddle tanks. I purchased the truck a month or so ago knowing it was a little bit of a basket case. The previous owner removed the front tank (who knows why-he even left all the fuel pump/sender wires bare and hanging) but the rear tank is still intact and has fresh fuel in it. The fuel pump will only run when I give it 12v at the fuel tank selection switch. When given power it gives me 40psi at the rail. Pressure holds after I turn off the pump. Pressure also holds when cranking indicating to me that the injectors are not opening. I can watch the fuel pressure start to drop immediatly when I supply ground to the injector and open it. I figured I would tackle the fuel pump problem later since I can get it to work by giving it power. That problem seems a little simpler (famous last words I know.) JWC-3, I have thought about adding a ground to the injector circuit. Here lies the problem (correct me if I am wrong-which is very possible ) The injector circuit is ground side operated. Injectors are given a constant 12v supply with key on. PCM gives it a timed ground signal to open/close the injector. At least this is how I understand it. Again, I could be incorrect. If this is correct I really only have one option when trying to strenthen my ground. I would have to add a ground going to the PCM. The PCM could then use the strengthened ground to send the ground signal to the injectors. From the wiring diagrams I have the PCM has 4 grounds. I have checked resistance from the PCM connector (PCM unplugged) to both a battery post ground as well as a body ground. There is less resistance from the connector to the battery post (.9-1.1 ohms) versus a body ground (2.0 ohms). Does anyone know where the ground locations are that feed the PCM? Is it attached to the body of the truck or directly to the battery? There are mutiple grounds all over to both the body and the battery, all of which I have cleaned, tightened, etc. But I am wondering if there is one I missed. Then again, it might not be a ground issue at all. I just don't know what else would be keeping my injectors from opening. Sorry for the lengthy reply. Again, thanks for all the response!!
Correct, you can not directly ground the injectors. The ecm control s that. You said you replaced the ecm. Used? Reman? Check the wiring close. Unplugg all injectors and see if the noid light flashes brighter. You may have a shorted injector or more.
The ecm/pcm is a reman. I am thinking that it is good since none of my symptoms changed when I swapped to the remanned from the old. Or in other words, my orignal pcm is fine and I wasted my money by partially "shotgunning" it as bad. I am not sure what you mean when you say to check the wiring "close." I will unplug all the injectors and see if the noid light gets any brighter. I hadn't ever heard of a shorted injector so I never thought of trying this. Good idea. Thanks again. I'll keep you posted.
Having been through this on my 90, next step for you, go over to the solenoid and tug on the fusible links The power to the fuel driver in your ECM is one of the fusible links, and I bet one blew, and the OP bypassed it
