Hi there. I am new to this site but it looks great. I have just purchased a 1986 F-250 with the 460 V8. It is an XLT with the C6 trans and dual tanks. It has only 70,000 orignal miles and spent almost all of its life out west so it is mint and rust free, and I mean mint. I love the truck and can not beleve about how great of shape it is in...*****cpt for one thing. It does not run very well or at all over 45 mph unloaded or 35 mph loaded or pulling a car trailer. It stumbles and tries to stall at those speeds. I have had it at my local Ford dealer several times and they are stumped. I was told by the dealer that they believe that this problem has been with this truck for a while becuase someone has changed a lot of parts and the problem is still there. Parts replaced before I bought the truck include :both fuel pumps, carb, fuel filters, and a complete tune up. Parts changed after I bought it include:spark box, ignition module, and a few small things I cant remember. It does this about 90% of the time. About 10% of the time it seems to drive OK. I can drive 50-60 miles and it is OK, but then the next day bam, it is right back. I need help please. My dealer says there is nothing more they can replace with out replacing the parts that were changed before I bought it. I dont want to part with the truck, but I have spent $1300.00 trying to fix it after buying it. Any help would be great!! Thank you for your time!! Bill

 

Sounds like you have fuel and fire checked out. I would do a leak down test and see what that tells you.

 

motojoe What do you mean by a leak down test? Is this something I can do? What tools do I need? What will it tell me? Thank you. Bill

 

This link will help with the basics

http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm

 

Is the exhaust plugged?