1970 Ford F-100 Question.

[Original67]

Okay by my signature and my build thread you all have seen I got a a a ........ yea its hard to say it. A Ferd. It's a 1970 LWB PS, PB, AC, Super Custom with a Big Block in it. I believe its a 390 but have been told its a 360. ummm not for sure. Here is the issue. Supposely when the truck gets to below a 1/4 tank it will just die. Ramdomly die. Only at or below a 1/4 tank. Had a couple of thoughts about this so I will put them out here. And before Travis or John says something about it "No keeping the truck above 1/4 tank is not the answer to this problem"

Thoughts:

1st Water/oily solution that is riding on top of the gas when the tank gets low it is able to slosh (SP) into the fuel pickup.

2nd Fuel line- when it gets low it is pulling enough of a vacuum to compress the line causing it to shut off. (Truck refires after sitting for a few minutes)

3rd Inner liner in the tank. I can not recall if these trucks had an inner liner in them.

4th (I know this will be the most common answer) Its a ford for a reason. Its suppose to be Found On Road Dead.

Okay everyone have fun tossing stones at this one.

this pic is from Wiki but looks just like it.
Attached Images

[Original67]

Okay update. Went home yesterday and the truck is seeping fuel out the filler neck. Opened the truck and it literally blew fuel out of it. Truck sit and pushed fuel out the fill tube for almost 30mins. Started it up let it run for about 15-20 then when to move it. Truck died would not refire. If I didn't know any better I would say the fuel is boiling in the carb from the heat of the BB. Thought that this was an eldelbrock issue not a stock 2 bbl issue. I am going to assume now that the truck has cooled down it will fire right up.

Feedback and Ideas please. Ford chevy still a motor with 8 pistons that wont run. Why do I keep getting these low miles trucks with issues. speedo say 29K and I have been told by family that it is correct.

[Original67]

Okay moved this from my normal area any would be great.

[NONHOG]

Just a wild ass guess here, vapor lock ? wrong fuel cap ? Is the fuel line under the truck near any exhaust ?
Sorry not much of a diagnostic tech but I can sure tear things apart pretty good.

Tried any F100 forums ? maybe its a common issue ?
Good luck and snap a pic or 2.

[Original67]

Everything is still original that's the puzzling part for me. Can't seem to find a reason for it to start doing this. I have only had the truck a week or so. guess its time to start the trouble shooting now.

[EVBuilder]

It sounds to me like there are two issues going on. One the fuel cap is not venting properly allowing pressure to build up in the tank. Two the sump sock is getting plugged with years of debris. It idles fine but dies under load is a typical symptom of that. It may be that the two issues are compounding each other. Try running the truck with the gas cap off and see if it runs better. Then pull the sending unit and see what kind of shape that sock is in. you may need to replace it. Running with out it is a bad idea and can destroy fuel filters and carbs.

[Original67]

I need to get a locking cap anyway so thats an easy fix. Now the sump sock thats a different story. Can't say I have ever replaced one of those. is this a pull the tank type of project. I ask only because I just but $60 worth of gas in the truck. thanks for the feed back.

[EVBuilder]

I am not sure on the Ford what is involved. I know that on my 63 GMC you can get to the sending unit by flipping the seat forward. It should be fairly high on the tank but that's a lot of gas. Those socks are a restriction even in pristine condition. When the vehicle gets old all the sediment builds up and makes them even worse. ripping it out used to be an old drag racing trick to improve fuel flow. but I would never recommended running without it unless the tank has been removed, thoroughly cleaned and sealed with some sort of gas tank sealer like the ones from Eastwood or POR.

[SCOTTMO]

the p/u tube on this is seperate from the sending unit,the p/u is part of the
tank from what i was just told.my partner says his 72 did not have a sock
on the p/u tube

[cdowns]

i'd take the tank out and clean it

[Original67]

Great information guys. This is why I like this site. I am going to start with a new cap and the next time my Chevy needs gas guess where it is going to come from. Yep the Ferd. Via a strainer of course. I will keep everyone posted.