I suspect your results come from the elapsing of time and not the adding of gasoline.

A dying ignition module that fails when it heats up and begins working again whenit cools off can give your symptoms. Would have been a good idea to check for spark & fuel as soon as it died but we're past that point now so I think it's a good time to get your sending unit and gauge wiring figured out while you've got all this apart. This isn't what's causing your no-run problems but it'd sure be nice to have a working gas gauge.

Do you have a volt/ohm meter?

 

I will also add that a full tune up is on the agenda for today/tomorrow, so maybe pulling the plugs will give us a clue? Is it possible that this is a spark issue in general?

That would make the fact that each time I've 'run out of gas' it's been in the first few gallons a coincidence and that would be sort of odd.

 

NO! DON'T CHANGE ANYTHING LIKE THAT RIGHT NOW!

By changing a whole bunch of things all at the same time, you then have a hard time figuring out where the problem is in the case that it now doesn't work (or work as expected).

You've got enough taken apart with your fuel system right now, don't go messing with the ignition right now, not until the fuel system is back together and we're confident it's correct.

 

Yes. We are definitely past that point now haha. Sorry for the run around.

I will be thrilled to have a gas gauge. It's the only thing that I haven't fixed on the dash. I plan to pick up the single reservoir unit I found on a Bronco tomorrow. I don't really need two tanks.

I don't have a volt/ohm meter, but I'm happy to pick one up today. I knew I'd need one sooner or later anyway. Do I need anything specific or can I just grab whatever looks decent?

 

Okay. That makes sense. That's good advice, thank you.

 

I'm confused by your use of single reservoir terminology? Do you mean - one gas tank?

You don't need a high-end volt/ohm meter for the basic tests you'll be doing, a $5 variant from Harbor Freight would even work.

We need the wiring diagram of the tank selector switch/dash gauge/tank selector valve/electric fuel pumps for your year. They've been posted before and are available, just need to find them. Maybe I can get Ralph to jump in.

In the meantime, figure out what kind of fuel pump(s) you have and where they're located and what powers them....

 

I've been reading about how the tank selector valves go bad frequently. One of the options I've read about is to replace that valve with what people are referring to as a 'single tank reservoir' from late 80's Broncos, fewer moving parts = less likely to fail in the future, but you lose the secondary tank--which is fine with me.

I read about it here:

https://www.ford-trucks.com/forums/4...tor-valve.html

 

True. Maybe there are two things - it runs out of gas at the carb, and the tank is full. But, maybe the tank doesn't have to be full for it to run out, that is just a coincidence. If so, it doesn't tank much of a leak for the mechanical pump to cease pulling fuel. Been there, had that done to me. This should have come from the factory with the plastic fuel lines, which aren't prone to cracking, but with all the other changes it may have rubber at several points. And, I can say for sure that factory rubber lines are almost always bad by this point. Very inexpensive to buy fuel line in bulk and replace the short pieces.

Edit: Forgot, but if you check the sending unit out of the tank the readings should be from ~10 ohms to, at full, to ~72 ohms, with no open spots in between.

 

The selector valves you refer to are not for carbed systems. They require a fuel pump in the tank to functional at all, and are prone to failure by sticking.

 

Ok--good to know. Thanks for the insight.

Back to the drawing board!

 

Do you have your charcoal canisters hooked up? You might want to unhook the line that vents from the tank to the charcoal canister and make sure it's not plugged. I would also check the fuel filter in the picture you posted (where the tank selector is supposed to be) and make sure it's not plugged up. I have a similar setup as you and I don't think the factory carb setups had a filter between the tank and the mech. pump. It may not be the problem but you could have an unnecessary restriction there.

 

Instrument Cluster and Gauge diagrams

3 port selector valve fuel systems



6 port selector valve fuel systems with EFI or 460 with Hot Fuel Handling

 

Chris, I just came online and quickly read through this. It does not look like this has been answered... The 1986 F150 with 4.9L has the feedback carburetor with a mechanical fuel pump located just to the left of the distributor.

 

That's where mine is, and I went ahead and picked up a voltmeter today.

 

OK, cool! I'll try and spend some more time with this tomorrow.