Engine/Transmission (1994 - 1998) Shut Off Solenoid

[PKemp]

As always Howard is right. You might ought to fix the original problem first.



But that cable idea is very attractive afterwards.

 

[Howard Durand]

I am certainly not always right but, in this case, checking the starter contacts might save a lot of grief.

 

[nfox]

I am going to replace the shut off solenoid and the realy and starter contacts and hopefully the problem is cured. Oo.

 

[Howard Durand]

I can see no reason for the starter to remain energized after the engine is running.

I bought a heavy duty 12 volt battery relay on eBay and, when it comes, am going to put it in the starter cable and control it with the ignition switch.

It can be wired to close when the ignition key is turned to the start position and open when the key is returned to the run position.

If this works out the way I think it will, even if the starter contacts fail, it won't be able to keep running and destroy itself and/or the shutoff solenoid.

 

[jwilliams3]

Anyone have the part number to the solenoid?

 

[PKemp]

Howard: Isn't that just making the same circuit more complicated by adding a second relay and control circuit to it? You could accomplish the same thing by adding a cheap "knife switch" in the cable line and not have to fool with your ignition switch wiring or current loading problems. I have a diesel boat/motor that we have a "knife switch" in the starter cable just to keep people messing with it when its docked and it works fine even in a saltwater environment (it is insulated). Pull the switch and no battery power to the starter solenoid. You can try to start it with the ignition switch (which will click the starter's solenoid) but no battery power at the starter solenoid. The knife switch cost me $8. 00 at a local marine shop. Its 4" long and 1" wide mounted in heavy phenolic with a mounting hole on each end. Connections are molded in studs with brass nuts on each end.

 

[biggy238]

That knife switch isn't controlled by the key though if I am taking it correctly. His will electircally disengage when the key is not in the crank position.

 

[Joe G.]

I think what the important difference is that the extra solenoid will not share the start circuit with anything else. If it does happen to stick no big deal. The normal circuit can stick because of bad starter contacts and burn things up. A knife switch is a PITA because if you have to use it in a hurry you have to bail out of the cab and open the hood. Even on the commercial boat I used to run the knife switch would have been a pain if you had to get to it in a hurry. Pull the hatch open, scramble down a ladder, run across the engine room, try not to touch anything hot or moving when you do, and pull the switch.

 

[Howard Durand]

Kyle B is right, the only time the starter will be energized is when the key is in start position.

My first impulse was to concoct some complicated electronic control with a timer and a bunch of relays but sanity prevailed.

I don't have the relay yet that I plan to use so don't know how much current it requires to operate. I am planning on being able to connect it to the existing curcuit that controls the starter so there will be no added connectons to the ignition switch.

I had thought about a knife switch but the reason for not doing that is pretty well explained in Joe's comments.

I see this as protection for the starter and fuel solenoid without adding any further complication to an already unnecessarily complex circuit.

 

[PKemp]

Howard: Please tell us how this works out. Its pretty interesting. A diagram and pictures would be great once you've got it solved.

 

[Howard Durand]

I'll post a note on what I do and how it works out. I am not sure yet how much current the relay I have ordered will handle. It is an eBay offering that didn't say anything about current capacity but it looks like one of the old switches or relays we used to have on the earlier automobiles that directly energized the starter from the battery. They were either actuated via a dash mounted switch or by pushing a foot operated button on the floor.

It is actually an aircraft device labeled as a "battery relay" requiring 12 volts for operation.

 

[LarryB]

You saw it here first!!!!

I've been working on a simple preventative solution for this problem for a while. Here is what I have come up with. It works great so far but I haven't of course tested it under all conditions. Works perfectly on my truck and a couple friends' trucks too.



It's basically a heavy duty diode in the starter trigger wire. It stops the starter from being able to backfeed to the solenoid relay. This way when you let off the key the solenoid will function normally. I think Dodge should have added this little fix as a recall a long time ago.



Simple and easy to install in about 2 minutes. Just disconnect the small trigger wire on your starter, put the diode on the stud in place of the wire, and re-connect the starter wire to the diode. That's it!







Larry

larryb@fostertruck.com



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[Howard Durand]

Larry,



Looking at the circuit diagram in my service manual, I can see about three separate things that can happen to destroy the fuel shutdown solenoid.

The shut down relay or the starter relay, either one, can stick closed or the starter contacts can stick closed.

There may be something I am not aware of but I can't see how the diode is going to protect the shut down solenoid.



Referring to my earlier post, putting a heavy duty solenoid in the battery feed to the starter will help prevent damage to the starter and solenoid in case of starter contact failure. It won't protect the solenoid if either of the other two relays fail.

I haven't found a battery solenoid yet that I want to use to disconnect the starter.

The one I found on eBay would probably work but am looking for one more suitable for the project.



Howard

 

[Turbo Thom]

I want to thank everybody for this post. It's one of the most interactive, intelligent, informative one's I read yet.



. . Preston. .

 

[LarryB]

Hi Howard



You are correct in the fact that the diode will not protect against the stuck fuel relay, however, this relay almost always fails to close, not open, and seldom is the cause of fuel solenoid failure. Fuel solenoid failure almost always starts with the starter contacts. This diode does protect against backfeed from stuck starter solenoid contacts.



When a starter sticks on it is caused by the worn contacts arcing and becoming welded together. When this happens the solenoid coil back-feeds 12v up through the trigger curcuit to the 70amp fuel solenoid relay. This is the part you're missing. The relay then thinks it getting the power from the ignition switch so closes the relay and energizes the fuel solenoid via the "pull" coil. This is why the engine won't shut off by the key. This "pull" coil is very strong but low resistance so will overheat very quickly if allowed to stay energized. This is what causes the fuel solenoids to burn up.



So, by installing a one-way diode and preventing the starter from backfeeding the fuel solenoid curcuit we save the fuel solenoid from burning up if the starter sticks on, again, the primary cause of fuel solenoid failure.



I agree it doesn't protect the entire system like your method does, but it's a very simple fix that will protect the fuel solenoid from the primary cause of failure.



Larry

 

[Howard Durand]

Larry,



You are absolutely right about the diode. I had my head in the netherland when I wrote that last entry. I apologize.

As you pointed out, It does prevent flow from the battery through stuck contacts back to the shutdown relay. It is a simple and very inexpensive way to protect the solenoid. Like you mentioned, why didn't DC think of that?

Probably because they make more money replacing burnt up solenoids than they could installing diodes.



I am still interested in using a battery solenoid though. It could possibly save the starter in a stuck contact situation.

A problem with that approach is that you probably wouldn't realize that the starter contacts were stuck if it did happen but an LED connected across the battery solenoid and mounted in the gauge pod could be used to provide a warning that you likely wouldn't miss.



When I get the right solenoid, I am definitely going to install one. I think I'll also put in a diode too. I am still running with the original contacts in my starter and have in excess of 100K miles.



Howard

 

[PKemp]

This is good stuff!! Oo. May I inquire: would it be a good idea to encase the diode in shrinkwrap to protect it from the elements? Or is this not necessary? Or... . You know that liquid stuff you can dip plier handles in to insulate them? Would that be a consideration? Look at: http://www.plastidip.com/industrial/liquidtape.html

And where can I get one of these? Diode P/N?

 

[LarryB]

That's what I'm working on now. A protective sleeve in case the diode gets bumped and bent. The whole thing is +12v so a short to the grounded starter case would not be a good thing. :{ I have it pretty well worked out and will maybe have some pictures here in a few days.



At first I installed a smaller diode on the inside of the solenoid chamber. This protected the diode from being bumped, was real clean when finished, worked great, but added a lot of complication as far as installation goes. Starter removal, disassembly, soldering, reassembly, and re-installation. A real pain and there's very little room in there. I also wanted a larger diode for overkill just in case. So this is where I am now.



I have ordered parts to put a few together for the first run and should have them available in a couple weeks. I'm shooting for a price of around $25 by the time all the screwing around is done. You could do it cheaper yourself, if your time and effort are free. Unfortunately the people I work with insist on getting paid.



As soon as I have some ready I'll post it here first.

Thanks for the input, all ideas appreciated.

Larry

larryb@fostertruck.com

 

[PKemp]

Larry: Keep me in mind please when your ready to put some up for sale and

Howard: Please keep us in mind when you've got the relay figured out. A most intriguing idea.

 

[PKemp]

I just thought of something else: could you put it together similar to a fusible link cable? That would keep the diode from exposure wouldn't it? Say a Piece of hard plastic tubing, put the diode inside with the wires soldered on each end and then fill the tube with epoxy. That would do it. Sealed, waterproof and safe from the odd "ground" contact. . (or off-road ride)... and still somewhat flexible... . you could even put a water-tight bullet connector on the wiring harness side filled with dielectric grease and make it easily replaceable (should such a thing ever be necessary)... .