Ok so while going down the road in my dad's 89 F250 we will drive fine then when it starts getting warm about 20mins after running and driving it the truck will start chugging like it is running out of gas. Then next thing you know it stalls out. You pull over and start it no problem will drive all the way into town no problem. On the way back though it started doing it again so my dad down shifted and it smoothed out and drove right along. I have so far replaced the TFI module, put a used fuel pump in, put more gas in it, new fuel filter and it drives fine until this starts happening. What do you all think is wrong? Coil? IACV? It will kinda lower its RPM right before dieing too. I thought maybe it might be the IACV (idle air control valve) because the truck stays around 400 or 500 RPM but when I first got it running it was at 900RPM and I believe that's where it is suppose to be.
Also the truck is a 89 F250 4x4 351W with ZF5 transmission. If you need more info on the truck I can help you out. The rear fuel tank filler hose currently isn't on could this cause it (I currently have it plugged really good with a rag).
Trav

 

Bumping this thread up again but have some updates.
I replaced the coil and condenser and the truck still is doing it. Now it idles at 850 RPM. I am really confused by this. My dad thinks it might be the stator (pick up coil) in the distributor. Really starting to drive me nuts on this truck. Maybe a bad vacuum line somewhere?
Trav

 

Try, for now, unplugging the IAC and adjusting the idle with the throttle stop screw.

 

The truck will run without the IAC? Will that verify that the IAC is bad?
Trav

 

Bad idea. Do not move that screw. While it is not the end of the world you may make things worse in the long run.

 

Yes the truck should run but the idle RPM should be very low. If the idle remains high you have a vacuum leak. If it drops then the issue is electronic.

 

ok so I took it off this afternoon and it ran very low (500 or so RPM). Put it back on right away as I didn't like the sound of the truck. Took the truck to my buddies place (5 miles away) and stuttered halfway there, in his driveway, and half way back all 3 times I turned off the truck and it started back up like nothing was wrong and drove fine. The 18th I am going by the local parts store so what list of things should I grab off the truck to test? Can I test any of these without the parts store? This is driving me and my dad nuts not being able to figure it out. (by the way not sure if it matters but the fuel gauge stays over full when running then goes to 3/4 when off. I believe this is the sending unit in the tank but don't want to drop the tank a 3rd time).
Trav

 

Ok so yesterday I replaced both in tank fuel pumps brand new this time and had my dad take it into town and no problems at all. Fuel gauge works again.
Trav

 

Glad to see the truck is on the road to recovery.

 

Ya now just to plug the rear tank, get the cruise fixed (ABS sensor is broken), and fix the radio then this truck will be good and on to the next projects.
Trav

 

Ok so the problem started up again yesterday. Took the truck 8 miles or so stopped got $30 worth of gas took off toward town and started chugging like crazy no power at all my dad pulls over turns off the truck waits a couple seconds starts up and heads back to the gas station. Stops there shuts off the truck talks to the neighbor a few minutes drove it home and chugged a few times but never stalled or loss of power. This is the most confusing thing ever. I drove the truck the past 3 days no problems at all runs like a top idle stays around 900rpm or 850RPM has tons of power while driving sounds great, I just don't get it.
What could it be?
O'rielly told me that one of the worker's daughter experienced the same thing changed the fuel filter FOUR times and then it ran fine??? How can a fuel filter cause it to happen once in a while and not all the time? I just put a fuel filter on it has maybe 150miles on it if that.
I know the truck needs a 6 liter tune up but I can't believe that this will cause this problem. All the parts above are the only parts replaced so far. I need to get this fixed instead of throwing tons of $$$ into it and it isn't fixing the problem.
Trav

 

subbing, my 460 is chugging like this too, just started doing it today, I dont think a fuel filter would cause this type of intermittant problem

did you try checking your fuel pressure

 

No I don't have access to a fuel pressure gauge right yet I will try and see if I can get one. I don't think a fuel filter does either but if my fuel filter is under warranty I am going to try and replace it if not I am going to wait to see responses.
Trav

 

Ok so I took the fuel filter line off right before it shook the filter and line a bit had a bit of dirt come out not much and took the truck all the way into town and back no problems. My dad is going one more time about 80miles round trip and will update if it drives fine or not. Strangest thing ever. Only thing I noticed is while driving when you press the gas on the passanger side you hear a metal tapping like noise it sounds to me like from the cat so maybe my cat is going? If it is I can cut it off and just pipe it and have no problems right? I have it that way on my 88 F150 302 so I don't see why not. I don't have emissions testing so no worries there.
Trav

 

If the fuel lines sat open for a long period of time, it's possible that there's enough dirt/dust/crap in there that would plug up fuel filters.

Gotta start with the basics though. Fuel pressure, ignition components (plugs wires, etc, what kind of shape are they in?). Make sure the distributor clamp is tight, no vacuum leaks...