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1993 F150 4.9l Cranks, Has Spark, No fuel pump prime
Hi Everyone, a couple weeks ago i went to pull out my truck to jump-start my neighbor's car. Of course it didn’t start, kind of ironic huh. I’m pretty stuck right now though. I’ve replaced the EEC after finding a burnt-up capacitor & crispy section of the board, but still no fuel pump prime. The ground from the battery to the fender is good, both the EEC & the Fuel Pump relays are good. The fuel tank selector switch is brand new, and i’m getting power to and past the inertia switch. Any amount of help would be great. Before i forget, it’s a 93 F150 with the 4.9l and e4od automatic.
Stick a test light connected to battery positive and probe that Light Blue wire with Orange tracer at the computer. It should light up momentarily when key is ON.
Just spent a little more time on it, following the schematic with the light blue w orange stripe from the fuel pump relay to the self test plug i have continuity, as well as from the self test plug to the PCM connector. But as stated earlier, no voltage at that same wire on the PCM connector when cycling the key to run.
I totally missed that you're getting power after the inertia switch! That info did not register for me earlier haha. Do this please: unplug the computer to remove its ground path and connect a test light up to battery positive and touch that inertia switch wire. If the light doesn't light then you have a bad fuel pump, a broken wire to the fuel pump or a bad ground for the fuel pump.
SpartanX wrote: no voltage at that same wire on the PCM connector when cycling the key to run.
No voltage can mean the wire's grounded, which was what I wanted to check for using a test light to battery positive. But this wire should not be grounded all the time with the key on. It should go to zero volts (grounded) for the prime, then return to battery voltage until you crank the engine.
jreardon, i really appreciate your timely responses. Luckily tonight I figured out the issue. When this first happened I replaced the fuel tank selector switch because in my mind that is a very likely suspect with this issue. Turns out that I did replace the correct part (tank selector switch) but I was given a faulty replacement. Tonight I completely restarted the whole troubleshooting process by just tracing voltage using some schematics I found online. I had voltage up to the selector switch, so I almost condemned the pumps and ordered a set. But, I figured while I was there I would jump the constant 12v (red/yellow) and the respective pump power wires with a paper clip. To my amazement, both pumps primed. Going to pick up a hopefully *good* selector switch in the morning. Lets see if duralast fails me again, thanks again for your ideas and responses.
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