We recently acquired a 77 f250 4x4 4sp straight cab long bed with the 351m and dual batteries.

I may have left the key turned all the way anti clockwise for a few weeks. Oh course it is dead when I go to hit the key.

We attach our 11 f150 to jump it. I attach to the battery on the passenger side. Wait a minute and nothing happens just as dead. My father checks the jump leads they are on just fine. As he was sure I had done something wrong he hops in the truck.

He turns the key. The engine makes a very weak rotation, he stops. Gives it 30 seconds and trys again, very weak rotations but it is constant. This time he keeps the key turned, after 2 more weak rotations it is spinning as normal. Then he lets off the key it is still trying to start. He takes the key out of the ignition and waves it at me in amazement and it is still trying to start. I quick side step to the battery and yank the jump leads. It stops, key back in the ignition, nothing it acts totally dead again...nothing looked obviously wrong. I have no idea where to start here. Please help gentlemen, and posibly ladies.

 

All sorts of weird stuff happens with a weak or completely dead battery. Clean all the terminals and connectors in the start circuit. Charge the battery. Retest.

 

Sounds like a stuck stater cylonoid on the passenger side inner fenderwell or on the starter itself. I'd hammer tap both and the connect the battery and see if it is still doing it.

Hang in there fmc400 will get on here (hopefully and thankfully) and get you lined out with what exactly to do next.

 

X2 on the sticky relay (or possible ignition switch)

Pull the small wires off the starter solenoid (relay). If it still happens, the solenoid is stuck and needs to be replaced. If nothing happens, then the wire to the solenoid is energized when it shouldn't be and that would lead you to a faulty ignition switch.

 

Alright thanks guys I really appreciate your input. Ill try to get to it tomorrow, we haven't put even a tank of fuel through it in a little over a month and this pops up. Ill try and get some pictures. It has some rot in the floor pans and in the bed but the price was right. As usual when these sorts of things happen you guys and your ideas have my bacon. This site and the collective knowledge here is amazing.

 

Edit: Nevermind, did not fully read the OP. Probably an ignition problem as others already pointed out.

 

I got a 1979 a few years back that had been sitting for who knows how long and wanted to check the condition of the motor before i decided what to do with it .. I tried countless tests and replaced parts and only ended up with symptoms like you mention .. As a last resort I took the starter in to autozone and had it tested and it tested bad .. ordered a new starter and put it in and still it was showing to much load on it ..As a very last resort I pulled the distributor to see if the previous owner had the timing all off .. Set the distributor in on TDC .. Sure enough the previous owner had the distributor in wrong and the motor started right up .. I can't tell you how many hours I spent to come to that conclusion .. What I learned though is that it is one of the first things I'll check now when the starter is working way to hard to turn the motor over .. You never know the state a previous owner has left the vehicle in don't assume anything ..

 

Because of the dead battery, low voltage, and cranking, the amp draw through the starter solenoid would have increased. Dues to the way you say it cranked slower I'm led to believe it was on it's way out already. This is also the cause of the electrical circle of replacing parts... typically a battery will start to fail. Owner waits to replace it which means slower cranking while starting which increases amps and heat in the starter which will drastically shorten it's life. HUGE no-no in Diesels, the second a diesel battery(ies) start to fail it gets costly to not replace them.

Pretty sure you just found the magic breaking point of the solenoid... the extra load finished it off. Even if it still "works" I'm sure it's damaged inside and worth replacing.

 

79 is correct when voltage is getting low amps go up which causes alot of heat and prob melted the contacts in the relay or partially melted them

 

It was another 12 hour day at work, other responsibilities at home of course so I haven't gotten to investigate further. There are a few different ideas and I will report back when I dive on in. Thanks again folks

 

I'm positive it was because of the dead battery.

The starter solenoid stuck. Only two things will do that. A: a bad solenoid B: constant power to the trigger terminal. Since "B" never happens, your solenoid stuck. PROBABLY because of the dead battery.

For piece of mind, put a QUALITY solenoid in it. We just had this happen to one of our trucks. We got TWO bad solenoids from the parts store that kept the truck cranking after the key was off. THAT'S TWO JUNK SOLENOIDS, BRAND NEW IN THE BOX. "New" doesn't mean "good" anymore.

 

If your timing is not set properly and you create a condition where two cylinders are working against each other and continue to try and start it under those conditions you will continue to buy new parts until you check that the distributor is installed at TDC ..