2.3L ('83-'97) Hard restart issue with distinctive pattern

[turner]

Thanks Luke. I think (hope) I've narrowed this down to fueling. Just writing an update while I work through it so I don't forget what happened.

I decided today to follow one of the more obvious symptoms: that the fuel pump isn't priming while this no-start condition is happening. I used a logic probe on pin 22 of the ECU, which grounds the fuel pump relay to energize it while priming or running. It was working correctly. I've never used this tool before, really makes it clear what the ECU is doing.

Next I checked for 12V at the output (terminal 87) of the fuel pump relay during the period it should be priming (but isn't). That is also working correctly. So I'm thinking the problem happens between the fuel pump relay and the fuel pump (including the pump itself).

 

[turner]

I've backprobed the 2-wire connector at the fuel pump. It always reads 13-14V during the priming period, whether or not the fuel pump actually primes. 80% of the time it primes, the other 20% it stays silent. I can force this to happen by turning the key on and off repeatedly, it's not temperature or time dependant, just random. It always gets 13+V though, so I no longer see how it could be an electrical fault.

Guess I'm replacing the fuel pump!

Edit: and I've just realized there are two fuel pumps. Great

 

[ShhhhhDougsHere]

Before replacing the fuel pump, once you've taken it out look it over really good and see if you can see anything wrong with it. You never know it might be a loose wire inside the fuel tank on the fuel pump.

Good luck brother.

 

[SenorNoob]

Since you have power after the relay, what about the inertia switch? Maybe even at the pump?

 

[turner]

I removed the inertia switch (and shorted the two wires) pretty early on to rule it out. I've also confirmed both pump's connectors are getting the right voltage at the right times.

I went ahead and ordered an NOS motorcraft in-tank pump, if it turns out to be a loose internal connection, I'll have a spare! Might as well replace it at this age/mileage, and while I have the bed off. It doesn't prime when it receives voltage, which I assume made the in-line pump work harder, cavitate, etc. The in-line pump only primes 80% of the time now so that's getting replaced too. And fuel lines while I'm down there. I saw a post where someone said the expansion chamber thingy is hard to reassemble leak-free so I'm leaving that alone.

 

[SenorNoob]

I've never touched mine. I've heard earlier trucks had a filter in it. Can't say that I've ever seen one. Maybe a left over from the carb days?

 

[turner]

Yeah mine is the larger (non-filter) one, based on the photos I've seen.

 

[ShhhhhDougsHere]

@turner I've never messed with the expansion chamber thingy either.
To be honest I don't even know what your talking about.
And if it is what I think you're talking about the previous owner of my truck eliminated it.
It's sitting in passenger side floorboard not hooked up to anything.

 

[turner]

Alright, for posterity, the new fuel pumps fixed it. I'm fairly certain that what happened was:

1. The in-tank fuel pump died. Bench tested it and it is non-responsive
2. The inline (high pressure) pump picked up the slack, which caused it to fail prematurely (and intermittently)

After I replaced the parts, I turned the key to ON, and heard what the prime was supposed to sound like with both pumps working... I'm pretty sure the in-tank pump has never worked in the 4 or so years I've owned the truck, if that's possible.

Thanks all for the help