85 F250, 460, brand new Holley 4160 750cfm carb like a month ago. Since I finally figured out why the truck was eating fuel pumps she's been running reliably except for this one issue. I fixed all the vacuum leaks and tuned the idle mixture screws with a vacuum gauge.

Sometimes if I let the truck idle for more then a minute or two the engine just bogs down and dies. Usually starts right back up. It did this for a couple days then the problem seemed to go away. It was running fine, just wouldn't idle for very long. Now today I've been driving around all day and she hasn't given me any trouble, then out of nowhere the engine starts bogging down and dying while I'm driving and any time I come to a stop. I put it in park, turn the key, normally she starts instantly well today it took me like two minutes to get her to start again. And every time, it would seem to run fine for about a minute then start bogging down and dying again.

What gives? Carb is brand new, there are no vacuum leaks, and when this isn't happening she runs perfect. I don't get it.

 

What was wrong with the fuel pumps? It sounds like it's running out of fuel again. Are you still using the oil pressure switch to run the fuel pump relay?

 

Yes I still have the OPS connector jumpered. The selector valve on the frame rail was bad, so for now I bypassed it and I'm only running on the rear tank.

Anyway...it is fuel. I can get it to start, with some persuasion. But it runs for 30 seconds, give or take, before it stumbles and dies. When it starts bogging down, it seems that giving it throttle makes it die quicker. I started it and stood up by the front, when it started to bog down and try to die I hit it with some starter fluid and it would keep running until I stopped spraying.

I'm really getting sick of this truck's constant fuel system issues arrgh! Oh, I don't think it should make a difference, but today was the first day its been cold in my area. Last week it was always above 40, today it was below freezing for the first time this year. But she ran fine all morning, then this started happening again out of nowhere. Until today she has been starting and running perfectly for almost two weeks now, I thought I had all the issues worked out.

More info that may or may not be relevant. The other night I laid into it hard, full throttle from a stop up to the speed limit. She pulled hard, but when I let off she seemed to stop running for a split second, but another quick jab of the throttle and I was cruising again with no issue.

Before today the problem has not been this severe, and all this past week she would happily idle until I turned the key off, so I thought whatever was causing the idle-stalling had gone away. Is it possible its just bad gas in this case? I stopped and got a few gallons I'd say roughly ten minutes before this started happening today.

I'm at a loss as to what's causing this. If the fuel pump (number 7!) Is dead, the truck shouldn't start/run at all. But it does start and run for 30 sec or so before it loses fuel.

 

Through all your troubleshooting, do you have a method to hot wire the pump? I believe you can do it over that the starter solenoid on the fender. I would take the line loose at a easy place up front, put a long rubber hose on it and put it in a bucket. Hot wire the pump and see what you get.

A wild guess; You might have fuel tank rust and dirt problems. Fooling around and hot rodding stirs up the fuel in the tank, and also all the dirt and rust, and this plugs everything up. Been there done that. It's important to have a clean fuel system. If you find that's what it is, new fuel tanks are not too bad as far as price.

 

I dropped both tanks. The back one, which I'm running on currently, was already very clean and rust-free inside. The front one I am going to end up replacing, it was disgusting how much nasty black **** was in there with the stinky ten year old gas when I first dropped it. I cleaned it out best I could but there's still **** caked on the walls I couldn't get at with my scraper so I will end up getting a new one.

I'm really hoping this is just water in the gas. Its been raining a lot lately, it dropped below freezing for the first time...there could easily be some condensation in there. I'm letting it sit over night and tomorrow I'm gonna drop a bottle of HEET in the tank and see what it does. Sigh...

If that doesn't do it the next step will be hotwiring the pump and a pressure gauge.

 

If your truck has an EGR valve you should check it. I have been reading elsewhere that they will cause same issues.