Starter starts, then doesn't stop

[Boudroux]

I have two questions. Are the large fuses in the PDC supposed to have power at all times, even with the key out of the ignition?

Second, is the starter supposed to receive constant power even if the key is out of the ignition? If so does that mean the solenoid on the starter gets a secondary signal from the ignition switch to allow the power to the actual starter motor so it can do it's thing?

2000, 4.0 engine is stock.

I put in a new starter a month ago. It has worked just fine until yesterday.

I started up the jeep and heard a loud whining/screeching, not a grinding. I turned the jeep off but the motor kept turning over. I immediately turned the key back into the "run" position and she fired right up screeching away. I turned off again and removed the key, motor kept turning over. Not running, just turning over. Put the key back in, turned to run, jeep fired back up.

I left it running so I could get home.

Before I could dig out pliers and pull the starter fuse in the PDC under hood the starter threw in the towel and went out in a smoke filled fury.

Drive home and everything else seemed normal.

Obviously a new starter is in order but before going any further I'm wondering what could have caused the starter to get stuck on and remain engaged.

With the key removed from ignition I checked for 12 volts in the PDC and each of the big fuses towards the front had power. Maybe that is normal, I don't know however it would seem that at least some of them should not have power when the key is out of the ignition. Is it normal for the PDC to be hot at all times?

I read some about the ignition switch being bad. The only thing about that is when the starter was acting up and I removed the key the engine was not running, it was just being turned over by the starter. Once I moved the key to the run position the engine fired, lights worked etc. To me that says the ignition switch is working. As it sits now I can turn the key to accessory and to the run position and everything seems as it should. In the run position the fan blower is working, radio works etc. In accessory position radio works, windows work etc.

Because it took less than 60 seconds for the starter to grenade I don't want to put in a new one, hook the battery back up and hurt the new starter.

Thank you for the help.

 

[Digger87xj]

I'd tend to call it a fluke instance and chalk it up to that you got a bad starter.
You can use a test light and see if there is power on the solenoid wire. It should only get power with the key in the start position. Starter relay in the PDC could be bad. Yes it is normal for the large fuses to be hot all times, as well as many of the small ones.

 

[mechbullxj]

Do starters have a 90 day warranty?

 

[8Mud]

You have to understand the basics a little. The starter is basically three parts, the motor, the solenoid and the drive gear/bendix/over running clutch.

The solenoid is dual function. One function is it has large set of (high amperage) contacts, in effect a large relay. The other function is it throws the drive gear, using a set of mechanical forks, towards the ring gear.

The ignition switch, through the starter relay, activates the solenoid. The solenoid in turn closes the large contacts which are wired directly to the battery to turn the starter motor.

Usually when the starter doesn't disengage it is because a set of contacts has welded itself shut someplace. Either at the ignition switch, the starter relay or the large (high amperage) contacts in the solenoid. It is also possible the large slug (piston) inside the solenoid got stuck in the piston bore, in the activated position, holding the contacts closed. Also *remotely* possible the drive gear was stuck on the bendix and wouldn't allow the solenoid to disengage (relax).

The large contacts in the solenoid can loose (ablate) the coating or plating and can tend to weld themselves together. Excessive heat can also melt the coating and they may weld themselves together. One of the reasons they recommend not using a starter motor for longer than fifteen seconds and letting it cool before trying it again.

If pulling the starter relay in the PDC doesn't stop your starter, the only other thing that will, is unhooking the battery cable.

 

[Boudroux]

Thank you all for the answers and explanations. It is funny that all these years I've replaced stuff, belts, alternators, starters, etc because they break and never really given it a second thought.

Then one day a starter does something I've never seen before and it dawns on me that I actually know very little about the inner workings of this junk. Mud thank you for taking the time to explain in detail.

The parts store swapped it out under warranty and I just installed. All seems well so it had to be a bad solenoid on the 40 day old rebuilt starter I purchased. Hopefully this one lasts a little longer.