My 1977 Ford f-250 pick up has been a champ for me except for recently. I am not able to start it after shutting it off after driving for 5-10 min. Sometimes I can get it to turn over on the first stop however if I have to turn it over a third time the engine will not turn. It tries to turn but slowly turns like it has no power. If i continue to start the engine the battery (obviously) drains. It turns over fine if I get a jump. I have changed the battery, alternator, and starter. What is going on???
Vapor lock?
Does the fuel line run anywhere near the exhaust? That could cause it. Is the fuel pump in decent condition?
Maybe your fuel filter is clogged, or the filter in the tank?
It sounds like your problem is not so much that the engine won’t start, as it is that the starter can’t turn the crankshaft over at a reasonable speed. If so, then vapor lock is not the issue. You’ve replaced the usual suspects, so it must be something else. I would look at the starter solenoid relay (I think that the 77s had those), the battery cables (all the way to the starter), and the ground strap from the engine to the frame. If all of those are good, then have the starter current measured when it is failing. If the current is greater than the max spec, then it would seem that bearings in your engine are failing (very unlikely to happen in this way).
Is there an exhaust pipe the runs close to the starter? If so, a heat shield may be missing that prevents the starter from getting too hot. And when a starter gets too hot it’ll turn the engine over very slowly.
Tester
The heat shield is the easiest thing to make. They are a common necessary,made at home part for Fords. 6" X 8" is the (about) size. It’s held on with an exhaust clamp. Two holes for the clamp. Put clamp in position put shield on and put the nuts on. I like to RTV a piece of heatproof gasket material to the metal but that is a “luxury” item. Heat soak is a common old problem from the stone age. It wasn’t too bad in the ice age.
well, im sorry to say i dont have an answer for you, but i am researching about the 1977 ford f250, and am trying to find any information i can. could any of you help me out?