![]() ![]() To me it seems like I have an electrical short somewhere and have been feverishly been tracing wires looking for bad connections, pinched wires, or burned up wires. My truck runs fine one moment then completely goes haywire the next. It’s also possible to have an internal ECM fault which means no ground to trigger the relay.I own a 1989 F150 Lariet and have been experiencing problems with the electrical system. This may show up as a code for loss of PIP or something like that. It’s possible to have an ignition module fault which can then lead to an inoperative fuel pump. You should see it light up with the key on, go out after a few seconds, and then come back on when you crank the engine. This could be verified with a test light by connecting it between battery power and the tan/green wire in the diagnostic connector. The ground should reappear if the engine is cranked due to the ECM receiving the PIP signal from the ignition module. This wire provides a ground for the pump relay through the ECM when the key is first turned on but will lose this ground within about 2 seconds. The tan/green wire I mentioned is a splice wire that is tied into the trigger wire from the fuel pump relay to the ECM. After that it shuts off, unless the engine is being cranked over by the starter motor. The pump will run initially when the key is first turned on but only for a couple of seconds. (I should have added that pulling the codes might not be a bad idea just in case there is a loss of PIP code this being the signal the TFI module sends to the ECM which then triggers the pump relay based on that signal.) After 3 or 4 seconds of cranking the light should still be on. ![]() If the light is on, crank the engine over a bit. Take a test light and connect it to that tan/green wire in the diag. If it does not run then it’s very well could be a faulty pump relay. ![]() This could be caused by a faulty TFI ignition module, faulty ECM, etc. This means that for some reason the fuel pump relay is not getting a ground through the ECM. If the truck does run then disconnect the jumper wire. You should hear the pump run and the truck should start if this is a lack of fuel problem. ![]() Run a jumper wire from that terminal to ground. There should be a tan wire with a green stripe. Look at the diagnostic connector under the hood where codes are pulled. ![]()
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March 2023
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