Was it hot out? (duh, it's summer). Could it just be vapor locking?

 

No, the truck had set the whole time we camped. When I hooked up the trailer and got out on the highway it started "the struggle" again, missing, kind of just chugging along, I was lucky to get it home. Driving up to camp, ran like a champ, pulled like a freight train. I'm going to check float levels today, it's an old autolite 4100. It just confuses me because it has run like a top, then starts this stumble, etc. It's not a problem that appears consistent as you can see in my other posts I thought I had it licked when I replaced the fuel pump, ran fine for a few days, then back again, coil.......same thing, a couple days then back again. I really think I can rule out electronics as it has good spark and the plugs are not fouling. Not sure about a vacuum leak, it does seem to idle well, problem is under acceleration. Just keep plugging along......hate to throw the towel in and take it to a shop to find it's some simple solution. Duh!

 

Checked the screen in the tank recently? If it sits during the winter you can get rust in the top of the tank, that rattles loose and stops up the screen on the pickup tube.

You'll have those exact symptoms. Runs perfect when tinkering with it and starves for fuel under load. Seems like you've hit everything else.

The ethanol in our fuel now might break loose some gunk and do the same.

 

If the fuel lines are old the ethonol can also break down the hose interior. Only cost a couple bucks to change the rubber out. One at the tank and then at the pump.

 

Is there one under the cab?

There's been one in line on most vehicles I've worked on.

 

Can't answer for the Fords. My ole chevy had one at the tank and then one from the hard chasis line to the fuel pump. Pump to carb is hard line if from factory.

 

Might be a unibody thing. There is probably a way to run one metal line from the tank to the pump on the trucks. A couple of spots on my car prevent it from being a solid line.

I just wanted to mention it for the original poster, just in case.

 

How's the overall voltage at the battery when this happens? Light dim? Could just be running the battery down to the point where the Duraspark has a problem (if it is Duraspark, or points?)

 

Brand new Optima Battery, yes, it's a duraspark set-up. Basically stock with xception of new Accel coil. I'm going to be back at it this week-end. Thanks for all the help!

 

what is the model of the accel coil?

 

Well, brand-new battery, yes, but what's the voltage read at the battery terminals? Just wondering if something is drawing down the battery enough to do this.

The stock alternator on these trucks didn't put out a whole bunch of amperage. Are you using the truck to charge the trailer batts while you're driving?

 

Coil is the Accel replacement for the duraspark system, has the correct horseshoe connect, etc. I finally got back out to take a look at everything. Never have checked the gas tank pickup screen, that could be a REAL possiblility. Looks like I have to drop the tank to access the pickup. I'll get there sooner or later.