1985 F250, 460 big block, auto, 2wd

Okay, this one has me stumped. I got the fuel leak fixed today and went for a test drive. When I stopped at the gas station for a soda and went back out to start it, I noticed it was cranking really weakly. So I connected my jumpbox, plenty of power just no crank. Then while the jump box was connected I noticed smoke from the starter solenoid (or more accurately, the wires where they connected to it on the battery side). Figuring the solenoid was bad and that would explain the weak crank, I went and bought a new one. Here's where it gets interesting: Installing the new one, it was sparking like fireworks where the various wires connect when I tried to start the truck, and whatever it was doing overloaded my jumpbox because it went from FULL to RECHARGE and started smoking too, I'm just hoping I didn't fry it. I figured I got a couple of the wires on the wrong large stud. Changed em around, started right up but the starter kept turning after it was running, even after I took my key out the engine died but the starter kept turning until I disconnected the battery. Consulted a wiring diagram, well none of my wires match the colors in the diagram, go figure. So a little trial and error.

After the last four hours messing with it, I tried literally every possible wiring combination. Every combination yields one of two results- either a shower of sparks that would make July 4th jealous upon attempting to start, or the phantom cranking after attempting to (and usually succeeding) start. I turn it off and pull my key out and it just keeps cranking until I disconnect the battery or it goes dead, and it seems to go dead very quickly when this happens. So I ruled out any of the small wires that run into the solenoid causing the spark show, because I tried starting with various combinations of putting them one side or the other, and leaving one disconnected at a time in an attempt to determine the culprit. No good.

In addition to the big main wires (batt to solenoid and solenoid to starter) and the ones that plug into the S and I terminals, there are three others- one which I believe runs to the alternator, one which the truck apparently needs to be connected on the battery side to get any power at all, and a third which runs into some little gadget below the solenoid then into a harness which goes back toward the firewall. I thought maybe that was the ignition switch wire but I disconnected it and the truck still cranked when I told it to. None of the fuseable links in any of the wires looked burned. Under certain wiring combinations, the solenoid's two main terminals would get very hot, too hot to touch. Also under certain wiring combinations, it would spark a bunch AND phantom crank. Or maybe the wiring combinations are irrelevant and this is something else? Though I don't know how it could be.

Its currently stuck at the gas station up the street and I imagine that if it sits there past tomorrow, they will tow it. But before I go back up there and start messing with it again I need some new ideas, because I'm out of them. This has me stumped. Any help with this apparently unexplainable problem would be awesome.

I'm sorry I don't have any pictures, can't find my camera.

 

First off, what is a "jumpbox?" Is this one of those portable motorcycle batteries with a handle?

If you haven't done so already, you're going to to burn out the starter motor, blow out the diodes in your alternator, and fry the regulator.

The small red/blue-stripe wire comes from the ignition switch and tells the solenoid to connect the two large lugs and thereby supply power to the starter.

This red/blue-stripe goes on the S terminal of the solenoid.

Remove that wire when the starter continues to crank; if the starter is still cranking, that solenoid is defective out of the box.

There are other wires with fusible links that attach to the battery side of the solenoid - one receives power from the alternator to charge the battery, one supplies power to the fuse box & headlights, one goes to the ammeter on the dash. This is assuming factory ammeter & oil pressure gauge and not idiot lights.

Connections getting too hot to touch are indicative of too much current draw through too small of a conductor, which tells me either something is hooked up wrong or there are bad connections (including the negative (ground) connection between the engine & battery) that are heating up.

If the starter continues to operate after the engine is running and the small wire is disconnected, bang on the solenoid to try and get it un-stuck. You should then be able to drive it home where you can fix it correctly and properly.

 

Yeah, sorry, jumpbox is what I call it. Little battery box used for jumpstarting vehicles with dead batteries.

Yes, my truck has the actual gauges and not just idiot lights.

So this is coming back to the solenoid I bought being defective off the shelf? I'll go back today with daylight and check the battery ground. This truck sat untouched for the last seven years until a couple days ago. I expected it to have problems that needed fixing, just wasn't expecting them to be the electrical variety.

 

One side of the solenoid connects to the cable going to the starter.
EVERY other wire (except the tiny Red/Blue trigger wire) connects to the other large terminal.

If the alternator plug or its diodes are bad it will spark when hooked up and the battery will die *even with no key in the ignition*.
Be careful here. This can cause an electrical fire.

 

When I got it running I had the alternator tested for output. 13.72 volts and plenty of amperage.

Of course now its having some sort of fuel related issue, but thats another thread...

 

Definitely check the grounds. Your starter is probably on the way out if the grounds are good. Just went through all this myself. Starter solenoid was bad and the engine kept cranking, hit it with a hammer or pull the "s" terminal wire. I'd crank and start my truck and turn it off a few minutes later. I'd try to start it again and it would slow crank( had been happening for years). I had to wait til the truck completely cooled to get it to start again. I just replaced the starter and it starts perfectly every time. Now I'm battling a no spark prob. I guess it never ends. Good luck to ya and keep us posted.

 

Well I disconnected all the wires to the solenoid, and the primary wire that ran to the starter and cleaned all the connections with a wire brush, which seemed to help a little.

I also took the starter off and had it bench tested. It was noisy and got pretty hot to the touch but the testing machine passed it across the board...?

And yeah, it never ends. Of course a truck that sat for seven years is expected to have issues, its just frustrating...

 

The alternator diodes act as a one way valve.
If they fail or the plug shorts the battery will discharge even though it produces current when running.

You need to find the discharge.
A bad ground in the circuit will not discharge the battery when sittting, as you describe when you stopped for a soda.

You describe "fireworks" when you connect the battery.
The fusible links protect the wiring harness and should blow with that much draw.
The only thing left is the charge cables going to the alternator.
If you have a tester remove the alternator cable and check that cable for continuity to ground.
Reverse the test leads and check for continuity again.
If you have continuity in both directions the diodes are bad.

If hitting the solenoid when it keeps cranking stops it you have spot welded the contacts inside the solenoid because it is drawing too much current.
A failing starter can cause this and cause the sluggish hot starts as well.

 

My starter passed every time also. Then I took it in when it was acting up and really hot. Failed.

 

Ok so I replaced the starter and that solved this problem. Thanks for the good advice, Dave.

 

Glad to hear.

 

should the small s hookup on starter sol have power only in pre ignition or all the time

 

The Red/blue stripe wire at the "s" terminal should only have power with the ignition switch in start.

This is where the starter solenoid gets your signal from the ignition switch to connect power from the battery to the starter motor.

 

Only when the key is turned to the start position.

Edit: sorry for the late response, I had three threads open at one time.

 

thnx thats what i thought