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1984 Jeep CJ-7 Starter Will Not Disengage


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I don't think I understand how the starter circuit is supposed to work.  Can someone enlighten me?

 

Lets see... new starter, new solenoid, new ignition switch, battery at 12.7 volts,I haven't found a shorted wire yet.  When I try to start the engine I have to pull the light blue wire at the S terminal on the solenoid to get the starter to disengage.

 

Help please.

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forman...With the Motorcraft starter, the starter can stay engaged if the starter drive is sticking or binding on the flywheel or flywheel ring teeth. The solenoid chucks the drive outward, and the starter lever at the motor engages the starter and applies current.  If the drive cannot sling back after cranking (or key release), the heavy current continues to flow at the motor and turns the starter.  Another issue is solenoid closure from a "leaky" and defective ignition key switch.  A defective solenoid can also stick closed and feed current across the solenoid.

See whether the starter drive is sticky. Also see if the drive teeth engagement is too tight.  Remove the starter motor.  Properly secure the motor on the workbench.  Test the starter motor on the bench:  1) run a positive jumper cable from your Jeep's solenoid switch (starter motor side) to the starter motor's cable post and 2) run the other jumper cable from the Jeep's battery negative post to the starter motor housing (for ground).  This circuit simulates your electrical system.  Use the key switch, and see if the starter engages and disengages while testing on the bench.  (Using the same circuit that currently feeds the starter.) 

 

If the starter engages and disengages normally on the bench, you have a sticking starter drive when the teeth engage the flywheel.  This can be due to improper tooth mesh or a drive that slings out too far and catches on the flywheel teeth.  There may be damaged flywheel ring teeth that are grabbing the drive. 

 

If you suspect the ignition switch, leave the KEY OFF.  Out of gear, brake set and wheels chocked, jump across the solenoid switch small wire terminals to engage and drive the starter.  If the starter engages and disengages normally at the solenoid, you have a current bleed through the ignition switch to the key start post on the solenoid.  This would most likely be due to a defective ignition switch that's leaking voltage across the switch contacts.  Try this test first, its the easiest one.

Moses

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Thanks again Moses, 

 

I found myself alone in the shop with no way to perform the ignition switch test you suggested.  I jumped the solenoid across the main posts with the small wires on the S terminal (LT blue) and The I terminal (red with white trace) removed.  The starter worked perfectly and the engine ran until I connected the I terminal wire then the engine quit.  I connected the S terminal wire and tried to start again and the starter would not disengage.

 

A couple of photos to clarify:

 

post-140-0-25749700-1439643325_thumb.jpg

 

In this picture the wire on the left runs from the solenoid I terminal to the upper + post on the coil.  I really don't understand the function of this circuit, or why the engine runs without the wire being connected.  Can you explain?

 

post-140-0-26631700-1439642517_thumb.jpg

 

I mentioned that my solenoid is new but seems to be the culprit.  

 

 

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Forman...This could be a defective solenoid if the wires are properly attached.  I would have someone work the key switch while you probe the two small gauge wires with a voltmeter.  In different key positions (KEY ON and KEY CRANK/START), you should get a different voltage signal. 

 

This is straight logic:  You want to activate the start mode ("S" wire and post) at the solenoid when the key is in the cranking/start position.  The "I" or ignition wire at the solenoid sends 12 volts (non-resisted) to the ignition coil just during cranking.  The "I" post is not ignition coil 12V continual hot, this is only a boost to the coil when the solenoid switch closes and the engine is cranking!  Key released to the "KEY ON" position, the "I" wire's voltage should drop to the resisted voltage level.

 

Try this before tossing out the solenoid switch.  Also check the solenoid switch posts for continuity in various modes.  Be creative and determine whether the solenoid is shorting to ground.  (Engine dying sounds like that could be happening.)  This could narrow down to a defective solenoid, but rule out the ignition switch first.

 

Let us know how this turns out.  We can discuss your findings...

 

Moses

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I tested the voltage at the solenoid and the results were as follows:

 

Ignition ON

 

I terminal 7.7v    S terminal   12.2v

 

Ignition OFF

 

ZERO volts both terminals

 

Ignition start

 

I terminal 8.5v  S terminal 12.6v

 

The voltage at the S terminal with the key in run/on  mode would explain why the starter will not disengage...  I mentioned earlier that I had purchased a new ignition switch which did not correct the problem.  I tested both switches and took one apart to visually inspect and found them both to be in good working order.  As you suggested I had to get creative, I removed the plastic connector from the group of wires that connect into the ignition switch.

 

post-140-0-15854200-1439732637_thumb.jpg

 

Then reconnected the wires into the switch. 

 

post-140-0-34006200-1439732794_thumb.jpg

 

I measured voltage from the S terminal on the solenoid.

 

post-140-0-69969500-1439732991_thumb.jpg

 

I brought the meter around to the ignition switch and started removing wires to see if anything changed and when I removed the wire that carries voltage to the solenoid when the switch is in start/crank position the wire at the solenoid terminal still had enough voltage to operate the starter.

 

post-140-0-62245200-1439733243_thumb.jpg

 

I had to think about what else was common to the light blue wire that would possibly leak voltage into the starter circuit.  I found a electrical schematic on line and saw where the ignition module and ECU were possibilities.  With the volt meter still in place I unplugged the ignition module and saw the voltage drop.  I hope that the problem is resolved with a new module but I plan to poke around and look for faulty connectors and hot spots before I purchase one.  

 

Any suggestions Moses?  

 

 

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Forman...First off, it's a definite that the lighter gauge "S" wire should never have voltage in the KEY ON position.  This is the issue as you note.  The only question is "why" there's voltage at the "S" terminal.
 
If the wire itself (disconnected and probed) reads 12V or so in KEY ON mode, then there's a source.  I would read the ignition switch start terminal voltage, not just at the solenoid.  Specifically, I would want to know whether there is 12V available at the start wire terminal on the ignition switch.  This would be with the start wire disconnected from the ignition switch.  By doing so, you will know whether there is voltage going through the ignition switch to this terminal post with the KEY ON.  All other wires than the start wire should be connected to the ignition switch when you run this test.  When testing, ground the switch body to simulate the switch being installed.
 
If there is no voltage available at the start terminal of the ignition switch in the "KEY ON" position, yet you're getting voltage at the solenoid end of the start wire, you have voltage crossing over to the start lead.  There has to be a source for solenoid "S" terminal voltage (the 12V or so) with the KEY ON.
 
Sources for this voltage would be either 1) a short across wires that involves an ignition hot wire and the start wire or 2) "switched current" (ignition switch or a device that might be able to feed current to the start wire).  If that includes the module or the module harness clip (shorting or arcing), then you need to test further.  You obviously have 12V available KEY ON to the "S" wire.  The voltage source needs to be identified.  The module itself could be a short or voltage source.  You describe how you interrupted the 12V to light blue "S" lead by unclipping the module.  Does the engine crank and stop cranking properly with that connector unclipped?
 
When testing for voltage at the solenoid wires, I'm presuming that you're not reading/probing the "S" terminal stud but rather the "S" wire feed.  This should be tested two ways:  1) Check the disconnected wire with the KEY ON and 2) check the terminal stud "S" for voltage with the wire disconnected and the KEY ON.  If there is an internal short in the solenoid switch, current could be feeding to the "S" terminal from a 12V source.  Battery connected and KEY ON with the "S" wire disconnected at the solenoid, test for voltage at the "S" post.  If voltage is present, the switch could be shorting between "I" and "S" posts or between the battery lead and "S" post, carrying either "I" voltage or battery voltage to the "S" terminal point.  This could be an internal short in the solenoid switch.
 
There's either a shorted solenoid switch or a 12V current source to the "S" wire.  Check the ignition switch as I described, the module and module harness clip.  The clip looks rusted.  Somewhere in the circuit there's a source of voltage to the start terminal in KEY ON mode...
 
Moses 

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The KLR you helped with the engine rebuild has 2500 miles since being rebuilt, no leaks no oil usage no compression loss.  My radiator is not in the best shape I could use a new one but I was wondering what you thought about wetting agents added to the coolant?  My son's truck is fine I believe he is about to replace his brakes as the truck is beginning to pull to the right when he brakes.

 

Your magazine is doing awesome keep up the great work!

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Forman...Really pleased about the KLR...Perhaps you could post an update (at the dual-sport forum) on the reliable machine that you created from parts!  This would be a real inspiration to KLR owners and other dual-sport riders.  The budget would amaze many, and you're paying for the bike with fuel savings.  Good time of year to ride...Take your camera and park at those places where you capture those fantastic wildlife photos!

 

Moses

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