M1114 Electrical Short Issue

[Woodshumvee]

Believe I have chased down the problem but wanted to get some input. I have been working my way through an electrical short on a M1114 I just purchased. Went to hook batteries up an had some arching/flames at the terminals. Started doing some continuity testing between ground and positive in the battery box and found a short on the buss strip. Found that the positive cable the goes to the KDS box (81A) was grounding out. I messed around in the engine bay for a bit as wiggling wires seemed to break continuity. I found a little chafing but nothing that would ground out. With my tester buzzing, I pulled the plug engine bay to the KDS box and buzzing stopped. I checked continuity on the plug side and everything was good, no continuity. Now focusing on the KDS box I identified that I have continuity between Pin E ( positive battery input) and Pin I (output to starter motor). I pulled the box apart to have a look inside and there are no signs of burnt wires or anything that would suggest an issue. I'm on my way to pull another KDS box out of a Humvee to test it out.

Am I correct to say there should not be continuity between any pin with the KDS box disconnected? How could continuity with two positive wires at KDS cause continuity with ground?? With a functioning box I would imagine Pin I is only on temporarily to tell starter solenoid to engage. Right now it would seem it is hot all the time when the battery is on. Thanks in advance.

 

[TOBASH]

For your edification. First schematic should help. Next should show you how to rebuild.

How to bypass PCB? I am aware some HMMWV owners have done it.

I'm not trying to speak sacrilege here, and I don't want to precipitate a war of words. :shock: How might I build a manual control box? My 24Volt Landcruiser just uses a glow wire to show glow plugs are ready, and then she just starts right up with the twist of a key. Civilian 6.2 Diesel...

www.steelsoldiers.com

 

[Woodshumvee]

@TOBASH thanks for your response. Bit to unfold but helpful for bypassing. Although I still have a shorting issue...

As I suspected the other KDS I pulled this morning has no continuity between Pin E and Pin I on the box or any pin for that matter. I also just checked each pin on the plug side against a ground and found that Pin I is shorting out, Pin E does not have a short. Ill need to pull the ignition wire off the starter solenoid and figure out where the short is. Also check to make sure solenoid isn't shorted/burnt out. I'm thinking the short messed up something on the KDS box causing the issue with continuity between Pin E and Pin I. Seems like box will need to be replaced ounce I sort out the short. Its always fun undoing what Govplanet does to these things.

 

[Mogman]

The wire 74 (pin I) will show very low impedance (resistance) to ground.
I just measured one at 2.5 ohms
If there was a short between positive and pin I it would try to kick the starter in when you connected the battery and would certainly cause a flash.

 

[Woodshumvee]

@Mogman Ill check what i have for ohms but based on the spark and melted battery terminal id say its more than 2.5 ohm. I tried just touching the terminals to the battery, lots of sparks and no starter noise. cant leave them on as it will probably catch fire. Thinking of disconnecting 74 from the solenoid, testing continuity and testing the solenoid by itself without 74 connected. Maybe solenoid shorted itself?

 

[TOBASH]

You probably have a blown PCB. Replace or rebuild.

 

[Mogman]

@Mogman Ill check what i have for ohms but based on the spark and melted battery terminal id say its more than 2.5 ohm. I tried just touching the terminals to the battery, lots of sparks and no starter noise. cant leave them on as it will probably catch fire. Thinking of disconnecting 74 from the solenoid, testing continuity and testing the solenoid by itself without 74 connected. Maybe solenoid shorted itself?

One thing to consider, if that wire #74 was pulling all those amps it should show signs of melting, disconnecting and verifying is a good plan.

 

[Guyfang]

Its always fun undoing what Govplanet does to these things.

 

[Mogman]

Can you connect the cables with the PCB disconnected?

 

[Woodshumvee]

Here is where I'm at:

1. Pulled 74A off starter solenoid and checked for continuity between ground and at PCB plug end now no continuity, good. Touched 74A back on solenoid and I have continuity. There does not appear to be any burnt wires or excessive heat.

2. Checked continuity between lug on starter solenoid and chassis ground and there is continuity. I'm assuming solenoid trigger should not be grounded.

2. Pulled 74A off starter and connected batteries. Plugged in original PCB. 74A is hot all the time at starter solenoid. Tried my other PCB from running rig and 74A not hot.

Think I've concluded current PCB is shorted and 74A (Pin I) is hot all the time. Starter solenoid is fried and grounded out? I don't want to turn key and risk destroying another PCB is starter solenoid is cooked.

@TOBASH do you have an info on rebuild PCB vs bypassing. Id like to just fix the issue with Pin I but not sure on schematic to do so.

 

[TOBASH]

Think I've concluded current PCB is shorted and 74A (Pin I) is hot all the time. Starter solenoid is fried and grounded out? I don't want to turn key and risk destroying another PCB is starter solenoid is cooked.

@TOBASH do you have an info on rebuild PCB vs bypassing. Id like to just fix the issue with Pin I but not sure on schematic to do so.

Yours is an easy unit to rebuild. Rebuild is the preferred bypass. The schematics are super easy.

Happy to talk you through it. PM sent.

 

[Mogman]

Here is where I'm at:

1. Pulled 74A off starter solenoid and checked for continuity between ground and at PCB plug end now no continuity, good. Touched 74A back on solenoid and I have continuity. There does not appear to be any burnt wires or excessive heat.

2. Checked continuity between lug on starter solenoid and chassis ground and there is continuity. I'm assuming solenoid trigger should not be grounded.

2. Pulled 74A off starter and connected batteries. Plugged in original PCB. 74A is hot all the time at starter solenoid. Tried my other PCB from running rig and 74A not hot.

Think I've concluded current PCB is shorted and 74A (Pin I) is hot all the time. Starter solenoid is fried and grounded out? I don't want to turn key and risk destroying another PCB is starter solenoid is cooked.

@TOBASH do you have an info on rebuild PCB vs bypassing. Id like to just fix the issue with Pin I but not sure on schematic to do so.

What trigger are you talking about?
You can connect the batteries without the PCB connected and run a test wire from the solenoid where wire #74 was connected and try touching it to the hot terminal wear a face shield and gloves

 

[Woodshumvee]

What trigger are you talking about?
You can connect the batteries without the PCB connected and run a test wire from the solenoid where wire #74 was connected and try touching it to the hot terminal wear a face shield and gloves

I'm referring to the ignition wire 74A as the "trigger". Yes I can connect the batteries without PCB connected. Batteries are soft so not sure ill get it turned over but with PCB plugged in and I touch 74A back to the solenoid I get a spark and seems like its stuck. Again 74A is hot all the time with ignition on or off so I know PCB is an issue. I also think solenoid is smoked as I have continuity from solenoid lug (where 74A) goes and chassis ground.

 

[Mogman]

I'm referring to the ignition wire 74A as the "trigger". Yes I can connect the batteries without PCB connected. Batteries are soft so not sure ill get it turned over but with PCB plugged in and I touch 74A back to the solenoid I get a spark and seems like its stuck. Again 74A is hot all the time with ignition on or off so I know PCB is an issue. I also think solenoid is smoked as I have continuity from solenoid lug (where 74A) goes and chassis ground.

You need to read the resistance, it should be around 2.5 ohms, would look like continuity on ether a meter or a test lamp.
The solenoid certainly could be shorted though.

 

[Woodshumvee]

Another update, not reading any resistance from 74 to ground but some other issues may have come to light....

With no PCB attached, batts are junk so I set my jump pack up for 24v, hooked up a power probe and manually activated the signal wire to the solenoid. I pulled off the inspection cover on the flywheel and when I send 24v to solenoid the start pops out and engages flywheel. Only issue is the flywheel isn't budging, the starter engages and locks up. I did this rapidly a few times to try and free it up but nothing. Batteries are defiantly junk but the jump pack should provide enough juice for a cough. Was going to try and spin motor by hand tomorrow, almost seems like its seized??? Oil looks good on dip stick though I haven't dropped fluids yet, just trying to get it turned over first. Thoughts on why I cant even get engine to turn over? Only other thing is starter is too weak to turn engine??

 

[Mogman]

I think on that engine you can take a 1" open end and grab the "spokes" on the front pulley. always try to turn the engine in a clockwise direction looking at the front of the engine.
Was the intake filter pipes intact?

Crossed fingers that it is just a bad starter or something else "simple"!!!

I have been told that using week batteries can cause damage to the PCB

 

[Woodshumvee]

Ill give that a try in the am. Looked and didn't see a center bolt on front pully but did notice the spokes so good to know.

Yes engine is completely intact with no missing intake manifold parts, intake horn, injectors, glow plugs, ect. Even looking a the underside and topside would suggest its been running recently with oil residue and wet spots....Although it doesn't take much for something to dislodge internally and seize it up.

I'm hoping for the best but starter seems to be "OK". When it engages you can see the body jump a little as it torques up. Would suggest that the starter is really trying.

Yea during all these tests I've got the PCB unhooked and on the work bench.

Ill throw a wrench on the front pully and see if I can get it to move without too much effort.

 

[Woodshumvee]

Put a wrench on the spoke and couldn't budge it. I'm afraid it may be seized. Now I own a 6,000 lb paper weight. Anyone got an tricks to free it up?? Anyone had any luck freeing one up? I've bought 4 non runners from GP in the past and this is the first seized one, bummer was not expecting that.

 

[TOBASH]

Remove all the glow plugs or fuel injectors. Pour in “Marvel Mystery Oil” through each open plug and leave for 48 hours. Then try to spin the engine with the plugs/injectors still out.

 

[Woodshumvee]

@TOBASH Ill give it a shot and see what I can do. How much oil do you typically put in each cylinder? I ordered a borescope to have a look around also. Going to drop the oil and have a look at it, oil on dipstick looks new. There's nothing that would point to a lock up so im surprised, but I cant get the front pulley to budge.