Truck is a 1983 F150 4x4, with a 4.9/300, and a 4 speed.

Truck has all new ignition, new gasket set throughout, and a new fuel system. The problem now is this: Truck starts, idles and drives great, 80% of the time. The problem is, as soon as I shift into 3rd or 4th gear, it will lose all power, start to miss and eventually die. I can push the clutch pedal in and it will start right back up everytime. It will sit and idle as long as you want. Sometimes it will do this many times during a drive to town or whatever, sometimes it won't do it for days. It has plenty of clean fuel, and carburetor is as clean as could be. I have always had ignition trouble since I've started driving the truck.

I've had a similar problem like this before, the culprit was a bad ignition coil in that case. I have since upgraded to an Accel 8140 coil. Truck ran and drove great for months after that. This problem has only surfaced for a week or so.

Any help would be greatly appreciated!

 

First welcome to FTE.


Ok do you know if your dist. have a vacuum advance can on it or not?
I ask because I don't know when they went to computer controlled carb & dist. and that will change how we go about testing things.


You say "all new ignition" what all was replaced?
I have seen it posted to check the horse shoe connector on the coil. I guess the become lose?
Dave ----

 

Yes, the truck has vacuum advance that works as it should. It has new pickup coil inside the distributor, cap, rotor, plugs, wires, coil, and ignition module. Also checked wiring harness and cannot see any breaks, cracks, or bare wires anywhere.

 

Clogged catalytic converter?

​​​​​​​What happens if you try to drive it in second gear at high rpm's?

 

Another possibility is the rubber hoses in the fuel lines. I've had similar problems where they were so porous that they would allow air in while running and that was killing the fuel pump's ability to pump.

There are rubber lines from the tank to the hard line, from the hard line to the switching valve if you have dual tanks, from the valve to the hard line, and then hard line to pump. If any of those are original they should be replaced as 1983 rubber wasn't designed for ethanol-based fuel.

 

I would have thought "The truck has a new fuel system" would preclude sucking wind, but I'm not sure *what* is new....

 

That's the problem when people say "I replaced everything." We don't know what their "everything" is, and if we assume something we may miss the problem.

 

Welcome to the forum!


X2 what Gary said in post #5.

 

The truck has a new fuel tank, sending unit, all rubber hoses, and all metal lines. It also has an electric fuel pump, but it works flawlessly.

The problem is still present if I drive it at anything other than an idle once it starts acting up. It may do it immediately or it may not come back for a few minutes. Sometimes it's days before it acts up again.

 

Try Jim's suggestion of shifting into a lower gear when it happens.

 

The truck runs poorly no matter what gear I'm in, or how I drive it, once it starts acting up. It will only idle, and idle as long as you want it to.

 

i had a problem like that (30 something years ago) when the Ford shop did some warranty work on my VV carb and put the fuel filter into the carb backwards. This paper fuel filter is a about 3/4 inch round with a hole in center that has a little check valve. The hole in the end needs to face the fuel line (inlet). When they installed the filter backwards what would happen is that at highway speeds (i.e. when there is a large fuel demand) the carb would run out of fuel since the filter was partially blocking flow into the carb. Then I would coast to the shoulder and crank the engine a few times (which refilled the carb) and the truck would start up and idle fine. The next time I got on the highway it would die out again after a few minutes.

 

Sounds pretty much identical to my problem. However the filters are facing the right way. The filters are only a week or so old. I may change them again and see what happens.

 

Okay, so it does this in *any* gear. .
...Not just 3rd and 4th.

If it were me I'd take the exhaust loose before the converter just to see if it will drive at speed.
A gasket is cheap, and troubleshooting is simple.

 

On a regular type carb (not VV type) you can just look down the carb throat (with engine off) and then move throttle linkage to full throttle, which will cause accelerator pump to shoot fuel out of accel nozzle (squirter) into carb. So if you see a stream of fuel shoot, then the carb did not run out of fuel.

It was mentioned earlier that a clogged exhaust has similar response (no power at high speed, but idles okay). I've not seen this problem cause the engine to stall/stop running though, but will certainly make engine run poorly.
An "exhaust back pressure gauge" is the correct tool to diagnose this condition, but if you don;t have one, you can also test by removing the O2 sensor or loosing the manifold to pipe connection so that there is "another way for the exhaust pressure to be relieved".