460 stumbling and dies on hills

[reverse_fault_frank]

My 1985 f250 with a 460 has recently started stumbling and dying while driving up hills at highway speed/rpm conditions. I've been unable to recreate the problem in the driveway. It seems like the engine is starved for fuel and if I let it sit for a minute or so it starts up and will usually get me back down the hill and home. The problem occurs on both tanks, I've replaced the fuel filter and the fuel pressure at the carb is about 4.5 psi. I've been driving around just fine in hotter weather and more miles recently and I have a bypass fuel pressure regulator to keep fuel circulating and prevent vapor lock. I've removed all the EGR system and made block off plates on the intake and EGR spacer. Recently the only thing I've done that may have catalyzed this stumbling was resetting the float heights in the carb. I had this problem before a little over a year ago and after replacing the battery wires, pcv valve, and a few other miscellaneous things, most of the issues in the truck seemed to disappear, but now its dying on hills again which is frustrating because I live in the black hills (plenty of hills here). I've seen this problem posted about on a lot of different forums, but I haven't found a clear solution yet. If anyone else has had a similar problem and/or knows how to solve this, I would appreciate some guidance.

Thanks,

-Frank

[Gary Lewis]

Frank - Might it be an ignition problem?  The DS-II modules and the pickup in the distributor can both cause similar symptoms when they get hot.

[reverse_fault_frank]

I spoke too soon. As soon as I posted that this was an issue on both tanks I had to go double check. The front tank was only putting out about 2 psi. I could have sworn it was both tanks, but I just went and drove up a big hill by my house and soared up it at 65 mph with no issues at all on the rear tank. I am now suspicious of the tank selector system and the front pump wiring.

[reverse_fault_frank]

Gary,

Is there a good way to test the module? Thanks for the speedy response.

[Gary Lewis]

The only way I know of to test the module is via a Rotunda test kit that the Ford dealerships used.  But even they won't catch the failing-via-heat issue until the failing starts.

However, if with all of the components hot you can sail up the hill on the good tank and not on the other then it has to do with the fuel system.  And at 2 psi I'd say the issue is the pump.