My fuel pump has been cutting in and out for a bit. At first I thought it had died but bench testing showed it was fine. So I guess it is bad wires bad computer bad fuel pressure switch? Instead of fooling with all that can I just straight wire it through a dash switch and turn it on when I start the truck and off when I stop?
Sure you can.
What you can do is, remove the fuel pump relay. Then on the secondary side of the relay socket, run two wires from the relay socket to a switch on the dash. The secondary side of the relay is always hot.
Size the switch and wires to handle ten amps.
And if possible, install a switch that lights up when it’s turned on. That way, it’s less likely you’ll forget to turn off the fuel pump when you stop the vehicle.
I have found that the EEC fuel pump enable circuit can intermittantly fail to trigger the pump. The EEC triggers the fuel pump relay by grounding pin #1
if you open the link a view identifies the pins. tapping into that circuit and connecting a small light
between the relay and a good ground will provide enough ground to turn on the relay while not causing a problem with the computer or eliminating the collision shut off switch.
The inertia switches are a common failure for this era Ford.
Has there been a history of intermittant failure on those switches? My only experience with them failing is when they trip and require resetting before the engine will run.
The failure rate probably isn’t really that high. Just seems like it when you fix around twenty Fords over a ten year or so time span fifteen years or so ago. LOL! I can remember that it wasn’t just pickups, but it seemed they were all using the same switches and yes I did fix about that many replacing inertia switches causing intermittent no-starts. Wasn’t really a common problem that I recall.
Well shit I direct wired the fuel pump and it runs the same. It runs well enough then blah. It will bog down for abut 10 seconds then stall or occasionally recover. Either way it runs fine again for a bit then bam it happens again. It almost seems like the ignition is turning off. Bad ground? Intermittent tank pump failure clogged fuel filter?
Hook up an indicator light in parallel with the pump to see if the pump is powered when the truck dies.
An '87 is one of the TFI ignition models that Ford had so much trouble with.The TFI module is prone to heat failure and this often begins with the onset of warmer weather.
I won’t go into the various tests, DTCs, and so on that are involved as those are available online.
There was even a class action suit over those modules and Ford paid out something like 200+ million dollars over them.
Direct wiring poses a safety problem. Direct wiring the fuel pump is not something I’d recommend. The fuel pump circuity is designed to turn off when the engine isn’t running. This is done to help prevent gasoline fires in the event of a collision.