Ok Guys I am a new member but I could really use some help. I know this type of problem has probably been talked about many times on here. But I need some advice/help on my specific problem....


Ok so first of I have a 1986 F350 460ci 4spd. 4x6 (dually) with 50,000 miles on it. The truck is a cab and chassis with a Rollback/ramp body on it.

When I drive it on the highway the truck feels like it runs out of fuel. The motor just cuts out. When this first started was only for a few minutes mainly when climbing a hill but, now it does it all the time. For a long time it seemed to be fine around town, but now I almost can't drive it...

In the last 5k miles or so I have replaced: Spark plugs, wires, cap, rotor, fuel filter in the carb, the pressure regulator (looks like a filter. T's of the fuel lines just before the carb), the carb has been rebuilt (professionally).

Last week I changed the front fuel pump & sending unit, also changed the rear pump and installed new plastic fuel lines w/ rubber lines connecting to the steel lines. Since then it seems to have gotten worse!!!

Also it will not pump fuel from the rear tank.. When i flip the switch the gauge changes as the is only about 1/4 tank of fresh fuel in there. Once the carb runs out of fuel in the bowl the truck dies out on the rear tank..

Any thoughts here ???? Please help I am going nuts trying to figure this out!!!!!!

 

What did the pickup in the tanks look like? A friend of mine had a 460, and found the "tee" at the carb with the return line was clogged with little pieces of plastic. These turn out to be coming from the pickup in tank which had disintegrated. Even though you have change this piece out, it may have clogged again.

Also what I would do is hot wire the pumps and get a hose and put it on the fuel line and run it into a bucket. That way you can troubleshoot the system. Here's a diagram of the system. Look for the pink/black wire over at the starter relay. If you jump this to the battery +, the pumps should run(the one selected).

 

The pick up looked fine in the tank.

Since I have last posted I am still having the same issue. I have Bypass the fuel tank selector valve with some steel lines that I made up. ( this was my rear tank not pumping problem)

I have also jumped out the oil pressure switch on the rear of the engine that runs the fuel system. I also replaced the fuel pump relay. The ignition module on the fender has been replaced too!

At this point I am at a loss with this truck! I have replaced or bypassed every damn inch of the fuel system and the truck is still running out of fuel on highway runs!!!

SOMEONE PLEASE HELP ME!!!!!

 

With all you have done, are you sure it's not getting fuel? When it dies, remove the air cleaner and look down inside the carb as you fully open the throttle with your hand. You should see two strong streams of fuel being injected; if you see that, that's a pretty good indication there is fuel in the carb.

Also see if you have spark to the plugs; there is a component inside the distributor that instructs the module to fire the coil at the right times....

 

The truck never dies like to the point it shuts off. If u read the description in the first post, when on highway and you try to give it more throttle there is nothing there. It will always idle and if you pull your foot out of it or pull over it will run fine.

It seems as tho when on highway and running a high rpm the fuel delivery cannot keep up with the demand of the motor. I am pretty sure it's not ignition related, I am an ASE tech and have been for many years but I just can't seem to get this issue under control. It does not feel as tho the ignition is cutting out. I thinking that I am going to have to try to rig s fuel pressure gauge to it and drive with it in the cab to see what the pressure does when it starts to cut out...

Generally those modules in distributor just crap out from my experience with them.

 

You have replaced everything on it, if your fuel pressure test turns out good, I would suspect dirt partially clogging on or both main jets in the bottom of the carb bowl.