Waine5550 Posted March 10, 2022 Share Posted March 10, 2022 Have a head scratcher on this one. The truck won't start. It will turn over. The fuel pump will prim for about 10 min then start. It will start fine for the rest of the day. The next morning same issue. New rebuild, and all new everything; however, I don't trust new parts. I have read all eec posts. Honestly I understand about 50% of the trouble shooting guide. I understand the concept of how this works. Eec relay and connecter is new so isn't the fuel pump relay. All help would be appreciated. 1985 f150 302 efi AOD 4x4. Link to comment Share on other sites More sharing options...
Gsmblue Posted March 10, 2022 Share Posted March 10, 2022 Are you sure this is an EEC issue? Better brains than me will jump in, but the first thing that springs to my mind is the fuel pressure regulator. Have you checked it? It is pretty simple to check. Cheap and easy to replace if the diaphragm is busted. Link to comment Share on other sites More sharing options...
archeman Posted March 11, 2022 Share Posted March 11, 2022 Are you sure this is an EEC issue? Better brains than me will jump in, but the first thing that springs to my mind is the fuel pressure regulator. Have you checked it? It is pretty simple to check. Cheap and easy to replace if the diaphragm is busted. First of all --- Not An Expert here there are much smarter folks who I'm sure will chime in. That said, if you're following a fuel suspect, get a fuel pressure gage on the fuel rail driver side test port. Key on - Engine off after pumps have run for abit, pressure should be 35-45 psi Engine Running should be regulated to around 37 psi Engine Running with regulator vacuum disconnected (unregulated at that point) should be 40-45 psi Link to comment Share on other sites More sharing options...
mat in tn Posted March 11, 2022 Share Posted March 11, 2022 First of all --- Not An Expert here there are much smarter folks who I'm sure will chime in. That said, if you're following a fuel suspect, get a fuel pressure gage on the fuel rail driver side test port. Key on - Engine off after pumps have run for abit, pressure should be 35-45 psi Engine Running should be regulated to around 37 psi Engine Running with regulator vacuum disconnected (unregulated at that point) should be 40-45 psi Wayne, I have been thinking over the symptoms we discussed. and reviewing documents about the different systems offered in 85. it seems to me that as a whole you have the efi offered in 85 with some modifications. the fuel rail is an 85 without the fuel pressure Schrader valve. I'm concerned about the pressure regulator not holding pressure first. if it is not "damming" up the volume of fuel flow then the pump will be nothing more than a circulator. another concern is a possible blockage between the pump and fuel rail. it seemed to be responding well to the pump and then bleeding off quickly after shutting it off. if you had both issues, they would amplify each other. I get very suspicious of aftermarket and non-standard parts even though they may seem to be an improvement. many times, I have had a truck or car come to me because it just did not want to go, and it would just be a fuel filter issue. when it is a cold start, it is at the point of greatest need for fuel pressure. and high enough pressure for good atomization as cold fuel does not give off enough volatile vapor. once warm there can be a reserve of volatile vapor allowing a lesser pressure/atomization to start the engine. your symptoms lead me to fuel management. the only quirk is the pump priming for longer than three seconds. Link to comment Share on other sites More sharing options...
Waine5550 Posted March 11, 2022 Author Share Posted March 11, 2022 This might not be related... while installing a radio into the oem harness, the ground is intermediate. I had to use a ground to the metal dash frame. Where is the eec ground point? Link to comment Share on other sites More sharing options...
mat in tn Posted March 11, 2022 Share Posted March 11, 2022 This might not be related... while installing a radio into the oem harness, the ground is intermediate. I had to use a ground to the metal dash frame. Where is the eec ground point? intermediate or intermittent? I don't know why but I felt I needed to ask. there is a possible "break in the chain" so to speak. the grounds are a weak link compared to voltages. the factory harness and component wiring use a lot of small grounds which for lack of a better description, just go to the first available chassis point. the dash is a ground point and it grounds through 4-6 bolted points to the cab. the cab grounds to the fenders and the block. the fenders ground to the battery neg. the battery negative grounds to the frame and the block on the large cable and the fender by the small link. this chain is sufficient but the proper use of paint cutting screws and washers is a must. just inside the opening for the radio on the glove box side there is a harness ground which usually has two wires under one screw. this uses the dash frame and therefore relies on the dash mounting points two of which are diagonal braces. one by the ash tray on the driver side at the bottom of the dash. the other is on the passenger side below the glove box. Link to comment Share on other sites More sharing options...
Waine5550 Posted March 11, 2022 Author Share Posted March 11, 2022 I see the eec ground goes to the battery. The part I don't understand is why won't the fuel pump shut off after prime. (2-3 sec) As soon as it does shut off (about 10 min) it will fire right up. This only happens first start of the day. I have a new fuel pump relay I will pop in next time it acts up. If it does it again I will change the eec. It's under warranty. Not sure what else to do. I will change out to a motorcraft fuel pump in the next couple weeks. Link to comment Share on other sites More sharing options...
Waine5550 Posted March 11, 2022 Author Share Posted March 11, 2022 I see the eec ground goes to the battery. The part I don't understand is why won't the fuel pump shut off after prime. (2-3 sec) As soon as it does shut off (about 10 min) it will fire right up. This only happens first start of the day. I have a new fuel pump relay I will pop in next time it acts up. If it does it again I will change the eec. It's under warranty. Not sure what else to do. I will change out to a motorcraft fuel pump in the next couple weeks. Gottcha Matt. Thanks. That will be my next project. Grounds grounds and more grounds. My gut tells me it's a ground issue. Link to comment Share on other sites More sharing options...
Gsmblue Posted March 12, 2022 Share Posted March 12, 2022 Gottcha Matt. Thanks. That will be my next project. Grounds grounds and more grounds. My gut tells me it's a ground issue. Did you check your fuel pressure regulator? Link to comment Share on other sites More sharing options...
Waine5550 Posted March 17, 2022 Author Share Posted March 17, 2022 Killed the gremlin today. It was a bad eec. The cardone replacement that I just swapped out had less then 200 miles on it. Needless to say it was the last thing I replaced. Thanks Matt for taking the time to answer all my rookie questions and thank to the others that helped me in the AWESOME forum. Link to comment Share on other sites More sharing options...
Recommended Posts