I have a 4.9 in this truck. I have been experiencing fuel related problems that I can't figure out. It first started bucking while going down the road like it wants to die, but doesn't. It does this off and on. Sometimes alot and then runs great for a while. I've replaced external fuel pump, rear fuel pump(it has the front tank removed), fuel filter, pressure regulator, new plugs and wires, distributer cap and rotor, tps, cleaned throttle body and iac, today it slowly came to a stop and will not start even though it has a full tank. Engine turns and has spark and the external pump runs even with the switch turned off. Oh, I also replaced the inertia switch. I am almost bald from pulling my hair out!!!

 

Let's see if we can come up with something you haven't done yet.

I can offer some things to consider;
1. You say the engine has spark, but is it at the right place at the right time?
How about this; remove the distributor cap , get the timing mark at TDC and see where the rotor is pointing. You may have to do this twice since #1 piston comes up to firing position every other time. What we are checking here is did the roll pin through the distributor gear and shaft shear? This can drive you nuts if you overlook it. It was a common problem with some of the units I worked on. With the timing mark on TDC the rotor should be pointing to # 1 spark plug wire on the cap. If not , check the roll pin.

2. For the engine to slowly die, sounds like you are running out of gas.
A shot of carb and choke cleaner into the intake while cranking will supply enough fuel to allow it to start if the fuel system is starving the engine.
If it starts , we can go from there. OK?

I don't remember if this unit is fuel injected or has a carb . Which is it? Thanks,,,,,,,,,,, hanky

 

I appreciate the info. I'll have to check those things out. It is fuel injected. I did find that the fuel pump has a loose wire so that's part of my problem solved, but the fuel rail has pressure and fuel. I'm thinking that the pcm could be bad. It looks like it could be the origninal one. It still has the ford stamp on the case. It still won't start and now I don't think it has spark. I did notice that the wire going to the resistor from the coil is bare in spots. Would this have any chance of shorting anything out?

 

It depends if it touches anything. Of course all wiring should be in decent condition if possible. Why is the wire bare in spots, has it been overheated ?
Sometimes those resistors open and you lose your ign supply to the coil.

I wouldn' go for a PCM yet until you know for sure its the problem.
Before you do anything else you need to make sure you have fuel and spark. Depending on which one is absent will determine what course you persue.
Its one thing if you have money to burn, then you can buy all kinds of parts and change them, but that is not the route to go.
To check for spark you already know how correct?
To determine if you are not getting fuel just shoot some carb cleaner into the throttle body , if the vehicle starts you have a fuel delivery problem.
Based on what you find will determine what we do next, OK. hanky

 

The resistor wire looks like someone has stripped it just before the receptacle. I sprayed some starting fluid and got nothing. I've also changed the ingition switch because the external fuel pump keeps running even after the truck is shut off. It still does it. The switch was old anyway. What would cause it to keep running?

 

Look for the fuel pump relay. It is staying energized when it should not. Once you locate it , you can unplug it and the pump should stop running. If it does , either the relay is hanging up or there is some source of voltage supply to it keeping it energized. If you unplug it and the pump stops ,reconnect it, if the pump doesn't start running again the relay is defective, if it starts the pump running again there is something sending battery voltage to it. Let me know what you find before we get involved where not necessary OK. Thanks,,hanky

 

I tried three different relays and it did the same thing. I disconnect it and the pump stops.Then I plug it back in and the pump starts again. I'm not great at chasing wires so any suggestions would be appreciated. I know it's supposed to be hooked to a 'hot at all times' wire. I don't know where to look though on the truck itself. It is always easier on the diagram. lol

 

In your vehicle (8th digit in VIN should be "Y" for 4.9 L engine)
Your fuel pump relay is controlled by the ECA (computer). We tried to eliminate the possibilities by the previous steps you performed. The next step is to replace the ECA. You were correct in suspecting it, but the right way is to isolate the problem which you did. This should eliminate the problems you experienced. Change the computer and have a good day. It is important to have all the correct info from the old ECA when you get the replacement.
The labels on it are important for correct replacement. hanky

 

I appreciate your time, info and your insight. I have a new computer on order and is coming in tomorrow. Thanks again.