I'm trying to diagnose a starter problem on our '95 F250 (Power Stroke) and I can use all the help I can get!

Yesterday my wife went to start the truck. I happened to be over by the barn at the time and she's cranking and cranking without the truck starting. Now that's not a surprise because it's colder out than the shady side of a you-know-what. But I'm thinking she's going to fry the starter motor so I signal to her to shut it off.

She jumps out of the truck holding up the key, and the starter's still cranking away. I run into the barn and grab the first tool I see, which happens to be the largest pair of Channellock pliers they make. I get back to the truck, get the hood open, and pry both negative terminals off the batteries without loosening the terminal bolts first. Somehow I didn't break a battery post in the process, and luckily the starter didn't burn up in the few minutes it was cranking away.

But the problem continues. If we turn the key to start, the starter cranks without stopping, even after turning the key off and removing it. It only stops cranking when I disconnect the batteries. I've tried immediately rehooking the batteries to see if it starts cranking again without the key, and if I can remember right (I'm getting a little confused by now) I think it did that once, but now it no longer does that. Now it only cranks if I turn the key to start, and then it won't stop until I disconnect the batteries. Nothing happens when I reconnect the batteries until I turn the key to start again.

I've tried gently rapping on the starter, the solenoid, and the starter relay, including during cranking but that hasn't made a difference

So I'm trying to figure out how to decide if the problem is that the starter solenoid is somehow stuck in the engaged position and I should replace the solenoid and possibly the starter as well, or if there's an electrical or mechanical problem at the ignition switch or in the starter relay on the fender. I hate replacing parts at random, although I've been known to fall back on that solution.

Does anyone have an idea of how to test for where the problem is?

 

I would start by checking the starter relay on the fender. With a test light,you should get a light on one large terminal with the key off. With the key in the crank position you should get the light on both large terms. When the key is in the run pos.,you should be back to power to one terminal. If you have power to both terminals with the key in the run position after cranking the starter, and starter is still cranking, the problem is the relay or farther up stream. If you have power to one terminal after cranking ( and starter is still engauged) It is the starter.
How are ht batteries? Low voltage increases the amps, and will melt the contacts in the relays making them stick together.

 

Thanks, Farmert. Your explanation makes sense to me.

As soon as I get brave enough to venture out there I'll find out what's going on. Is it as cold in SD as it is here in VT. At 11 AM it's up to 2 degrees, but with the wind chill, it's 15 below. Luckily the sun is shining.

Appreciate your help very much!

 

Oh, and you asked about the batteries.

I'm certainly running them down with all this cranking, but I'm putting the battery charger right to them each time, so I'm keeping the voltage up over 12 volts.

However, with all this cold weather, it could be low voltage that has melted the contact within the relay to cause this problem.

But then if the relay contacts are fused, how could they release so that there's no cranking when I reconnect the batteries. Even without the key on start, wouldn't it begin cranking again just by reconnecting the batteries? Or am I missing something?

 

Sounds like the relay is releasing the connection with the batteries disconnected and don't stick again until you crank on it.

 

Easy way to confirm this - loosen the nut on the terminal on the starter relay for the wire that goes down to the starter. Also have the battery negatives finger-loose. Crank the key, let it start to run away, then quick spin off the nut on the relay terminal and pull the wire. If the starter shuts off, that fingers the relay. If it doesn't (then you gotta pull the battery negatives), that fingers the starter, most likely the solenoid.

 

I appreciate all this advice, but I must be missing something....

Doesn't the power to the starter run through the relay. If so, wouldn't disconnecting the starter wire at the relay cut the juice to the starter, thereby stopping the cranking, regardless of whether the problem was in the relay or the starter?

 

I had this exact same thing happen to me a couple years ago. Shortly after I replaced a starter that went bad. Long story it was the dead of winter and wanted to make one trip to the store so I bought everything I needed, not caring if I would end up boxing it up and tossing it in the parts shelf. I replaced the fender relay, no fix. Then replace the original with a new starter relay, no fix. Ended up pulling a starter out of another fleet truck and swapping with my near new one. Problem gone. Put my 3 month old near new starter in the other fleet truck. It did the same thing it did in mine without releasing. Took it back and got a warranty starter and we were good to go.

There is a bendix gear in there that can stick. Even a near new 300$ NAPA starter failed quick on me. Guess that what happens when they are made in China, Mexico, and New zealand.... I wasn't paying $600+ for an OEM unit...that was still assembled in mexico

Not sure if this helps, but I'd just go grab a new solenoid and fender relay and try them both. If not take them back and get a new starter. Proper way is to test it like madpoguey explained above, but throw enough parts at it you will get it squared away :-) Not recommended though unless you have the coin and time!

The other option is a failing ignition switch, which I was about to pull on my truck, before swapping starters.

Best of luck.

 

How can a stuck bendix keep the electric running to the starter.

I have similar sporadic symptoms on my 95 F250. I have replaced the starter solenoid and the fender relay. The only thing I thought is the starter switch is ragged out. It seems to only be an issue with mine if its too cold outside like it is now.

 

because the bendix is attached to the solenoid.

here is how it works....

When you put the key in the crank position, the solenoid on the fender energizes the solenoid on the starter.

The solenoid on the starter does two things...

First it kicks out the bendix which is normally held back by a spring. Second, at the back of the solenoid is a pair of contacts: one running directly to the batteries, and the other to the motor part of the starter.

When the bendix is all the way out, a metal disc at the end of the solenoid shorts out the two contacts and causes the motor to turn.


The bendix rides on a set of splines that should be lightly greased. What can happen is if the grease has been eliminated (say by leaking fuel), the extra friction of torque on the splines that the bendix rides on while turning the motor could be more than the return spring.

When this happens, the bendix does not return and it holds the solenoid on the starter from returning thereby holding the disc to the contacts on the starter closed.

When you disconnect the batteries, the starter motor stops turning and the bendix is released.

If the splines on the shaft that the bendix rides on are also worn it can also cause this.

There is another failure mode where the contacts of a solenoid weld themselves to the contact disc but often (not always), when you reconnect the batteries the motor will start turning again.

My guess is that the bendix is getting jammed.

Have you had a fuel leak? You could take apart the starter and re-lubricate the bendix shaft.

You can kinda see a generic starter here...

 

And there you have it.

 

Now that was an excellent explanation. Thank you. I have never had a starter solenoid apart before to actually look at how it works.

Yes I have a fuel leak. Yes I will pull my starter and probably clean the crap out of the spline where the bendix rides at and give it a touch of grease. Im a bit reluctant about buying another as there is nothing wrong with the starter motor.

 

Yes I did have a fuel leak last summer. What's the connection between that and this problem? Is it that fuel could have leaked inside the starter and cleaned the lubrication off the bendix?

And BTW, I just tried the test that madpogue described, and when I disconnected the wire from the starter at the relay, it keep cranking, so I'm off to the parts store for a new starter. My thought is even though the problem could be within the solenoid and not the starter itself, the starter is old and could be worn as well, and it's too cold to do too much diagnosing lying there in the snow!

 

Yes. Its terribly cold and changing a starter out today in the snow is one sucking job

 

If you have a spare battery laying around you can activate the solenoid by putting ground to the body and power to the little terminal.

If you dont connect power to the big terminal, the motor will not start and you can just pop the bendix in and out to move the grease around.

Do note that there is a one way sprag clutch under the gear part of the bendix that has grease in it. It should be mostly sealed so when cleaning do not spray any cleaning fluid in the starter. Use rags and simple green or something to clean out the excess dirt in the nose.

Taking apart the starter is easy, but because of the brushes in the main body, it can be a real pain to get back together of you do not have the proper tools.

you should be able to remove the little solenoid without too much trouble.

Note, I have not had the PSD starter in front of me so I am speaking in generic terms.

Richard