Need Help

[blademan7]

1994 4WD with 4.0, truck won't start and fuel pump not running. I jumped fuel pump and truck started, while the truck was running I plugged the fuel pump back in and the pump and the truck stayed running. I shut it off and it wont start even if I jump the pump again. It has power to coil, and injectors and spark to the plugs. I'm thinking it could be the PCM but the part number on it don't seem to match what all the sites say it should be. So should I replace the PCM, and should I just get the one that all the sites say is the one for my truck?

 

[Earl43P]

No reason whatsoever to suspect the PCM with your symptoms.

Verify you have good fuel pressure at the fuel rail.

We could also use "more information" about this truck, such as Is it new to you, was it running fine for X months, then this just "happened", or you got it cheap and are trying to fix it, have no idea its history, etc.


In general, FP not running and has spark could be

Tripped Inertia switch (jumper its connector's two pins to absolutely rule it out while troubleshooting, leave it like that till you KNOW it's fixed)

Bad Fuel Pump, pretty common

bad Fuel Pump Relay, also common

Loose PCM Power Diode (but that would kill your spark too)

Bad ground, believe yours is located on the front fender under the hood, don't know if it's on the left or right. Just clean all of them up, including the one on the radiator support.

I looked at your other thread too.

If you have no power to the inertia switch then go after the FP relay.
IF you have power all the way to the top of the tank connector, either the ground is bad or the pump itself.

Verify fuel pressure is good at the fuel rail and a new fuel filter is also recommended.


I have schematics for 93, which should be the same as 94. PM me your e-mail address and I can send you those.