Hi Folks, New here and in desperate need of some help if you don't mind...

I don't know what category a 1995 box truck falls into, but it has a 351, so maybe someone here can help. It has been running inconsistently since picking it up. It runs well at idle but under a load it shudders and lacks power like it is bogging down then it will suddenly gain power and run smoothly for brief periods. It is difficult to get it above 60 mph...

Here is what I have done... Removed and thoroughly cleaned TB, EGR valve, IAC valve, tested TPS, checked and re-gapped plugs, changed wires, cap and rotor button and verified firing order. I am at a loss. Any help would be appreciated.

 

Does it have an auto trans or manual , does it loss power on the hills or does it matter?

 

Has the fuel filter been changed ?

 

Thanks for the ressponses.

It is automatic and it was acting up all the time, doesn't matter if on hills or not.

I was going to change the fuel filter but it was raining... But I did check the fuel pressure, it is 33 psi which is fine from what I have read.

I was going to read codes but it has the 7 pin obd2 port and I don't have a reader. So I drove it to Auto zone for them to check it. It ran poorly on the way over. Turns out they don't have the correct reader either. So I got in it to come home and it ran perfect! Absolutely no problems at all. I drove it around for another 25 minutes without a glitch. Now I am really confused. The only thing I noticed is that it seemed like it was idled up a little more than it should have been, but compared to before I have no complaints. What could it be/have been? I'm guessing MAP sensor?

 

Fuel pressure is only half of the story, volume is the other half. Usually if the filter is restricted it doesn't unrestrict itself. Could you have some questionable gasoline in the tank? That would not usually cause the check engine lite to come on either.
Has this truck been sitting somewhere for a while?

 

You might be on to something. I will change the fuel filter as soon as I get a chance.

It was very low on gas when I bought it and my guess is that it was sitting for at least a couple months, though I have no way of knowing... Maybe even longer.

Do you think it might have had water in the tank? Would old gas sink to the bottom for some reason? The change was so sudden it makes me think something changed instantly.

 

Moisture is not supposed to get into the tank, but it does.
A good PM move would be to change the fuel filter and add some drygas.
Wouldn't use any with methanol just isopropyl alcohol.

 

Late this afternoon I thought I'd go run an errand in the truck to see how it was doing... It was running like crap again. Then after shutting it off and going in to run the errand I came back out and it was running smooth again!

It doesn't necessarily seem to be that it runs bad when it's cold because I have driven it running bad long enough to warm up. It's only after I stop and let it sit for about 15 minutes that it starts running better. So what does this tell me?... I don't know.

I am going to change the fuel filter either tonight or tomorrow morning.

 

I installed a new fuel filter this morning and the one I took out looked just as new as the one I installed... I am obviously following in somebody else's footsteps.

I am probably just going to order the OBD2 Ford adapter. I am going to pull-a-part today so maybe I will pick up a map sensor and an egr solenoid... the two things I would like to try while I'm stabbing in the dark.

Still open to ideas. I think I can eliminate fuel as the problem unless the fuel pump is acting up and I tested it during a time when it was working fine.
Marc

 

Marc, Like a lot of folks it's fun spending other people's money, but to keep throwing parts and money at the problem gets to be expensive especially if it doesn't correct the problem.
The looks of the removed fuel filter can be misleading , what I carefully try to do is blow through the old and new filter the way the arrow shows, inlet to outlet, then make my decision as to whether its clogged. When you drained the removed filter did you get any water out of it?
If the EGR has carbon stuck in it , it could cause a rough idle , even stall.
You replaced the wires and stuff , why not the plugs? That could very well be the problem, I would suggest using Motorcraft plugs if you decide to change them.
Is this an E model or F model truck. There were some differences between the two models and the fuel systems.