URGENT HELP!: Fuse 26 keeps blowing...

[bigman]

Thanks. I have a digital multi-meter. This is what I used to check the PCM 12 and 25. I used the multi-meter set to the alarm setting. This way when I checked the pins to ground it would beep.

I will attack the wiring with a hatchet, the scalple is just not working! lmao

 

[bigman]

your theory of pin 12 and pin 25 on the PCM being joined together and going to ground.:disgust:

I checked this on both PCM's. 12 and 25 connect on the PCM side. They dont connect on the plug side of the PCM. 25 is grounded out :shrug:

I would think that if a wire were melted to another and grounding out, there should be a connection to be had using the multi-meter from pin 12 on the plug to another wire in the plug, theres not :freak3:

 

[bigman]

Can anyone check there PCM on 12 and 25..???? Perhaps they are not suppose to be connected and the PCM I bought was junk

 

[bigman]

Just to clarify, I have used both the test light and the digital multi-meter. The test on 12 and 25 has been done with the PCM out of the truck. No pins on the PCM ground out the body of the PCM.

 

[bigman]

Any wiring diagram on the generator source wire.??? Pin 25 is grounding out. Pin 25 is connecting to pin 12 inside the PCM. Thus, gounding out the OR/GR wire from pin 12 to fuse $26. I am sure this is the problem. Wire OR/GR is good from fuse to PCM. OR/GR is also good from fuse to injectors. As when I snipped the wire that goes to pin 12, it did not blow the fuse.

I also think that the multiple pins grounded out is the parent issue. What would cause a ground out like this? ignition switch?

This may be un-related but, I thought the starter might be going bad. As sometimes (randomly) the bendix would spin but not engage the flywheel.

Now that this fuse problem has surfaced, I can crank the engine and after about 6 seconds, the starter disengages the flywheel. The bendix is still spinning tho. Could there be an issue with power/ground causing the starter to do this? leading me to the ignition, leading to the massive ground out?

 

[bigman]

fwiw, I found this!

http://www.scribd.com/doc/2626312/Jeep-KJ-2003-Liberty-Service-Manual

 

[Billwill]

fwiw, I found this!

http://www.scribd.com/doc/2626312/Jeep-KJ-2003-Liberty-Service-Manual

Yes this is basically what I am using. It is worth your while to download the whole of Section 8, it has not only the circuit diagrams but also the locations, theory of operations on how things work eg. how PCM operates the alternator to vary charge current, simple fault-finding tips etc. This is about 42 Mb to download.
If you then look at sheet 8Wa-20-2 Charging System Gas you will see that pin 25 on C3 on the PCM, White/Dark Blue is the generator source ie. +12 or +5 volts...I am not sure, I have the CRD with an ECM not PCM. This wire goes to the two pin plug on the alternator which is the field coil. The other side of the field coil goes to pin 10 on C2 on the PCM via C104 pin 13, dark Green wire.. This pin, Generator Field, will get pulsed down to ground using a variable duration of pulse (Pulse Width Modulation) to increase or decrease the charge voltage.

 

[bigman]

well, I am giving it a break for a minute. A friend of mine lent me his summer truck to drive until I can get this thing fixed.

 

[bigman]

Will be getting back on this guys soon. I am going to follow the generator wire pin 25 back. This is the pin shorting pin 12. Still does not explain the multi pins grounding out? Anythought on the ignition being the culprit?

 

[Billwill]

Will be getting back on this guys soon. I am going to follow the generator wire pin 25 back. This is the pin shorting pin 12. Still does not explain the multi pins grounding out? Anythought on the ignition being the culprit?

The multi pins may seem to be shorting out but it could be the "de-coupler" capacitors that are used on most circuit boards are confusing your multimeter...I would not be too concerned about that.
I doubt it is the ignition but as I have seen, any wire can melt onto any other random wire so anything is possible.
You have the correct circuit diagrams....I am sure you will nail the bug soon now!:freak3:

 

[bigman]

^^^Thanks, I sure the hell hope so. Snow is about to fly!

 

[Neal]

The multi pins may seem to be shorting out but it could be the "de-coupler" capacitors that are used on most circuit boards are confusing your multimeter...I would not be too concerned about that.
I doubt it is the ignition but as I have seen, any wire can melt onto any other random wire so anything is possible.
You have the correct circuit diagrams....I am sure you will nail the bug soon now!:freak3:

Decouping caps are just for hi freg swiching noise--the meter should not see these as a low point to vdd.- usually .01 caps
Think it is time to start removing lines from cuicuit loop/string to isolated the grnd fault causing the fuse to blow.
Of course if you have umlimited money, just jumper the fuse and watch for smoke(just kidding)
More lines have to disconected to isolte to excessive current draw.

 

[bigman]

Update: PROBLEM FOUND!

I determined that pin 12 was being shorted out by pin 25. Pin 25 is the generator source. After unplugging the alternator side, the wire was still shorting out! My first thought was, the wire has melted to another. Before I cut the wire and ran a new, I went to unplug the connector by the battery tray. Low and behold the connector would not budge! The damn white/blue wire (from pin 25) was pinched and stripped under one of the nuts for the strut/coil.

Heading out right now to fix the wire and give her a crank!

Pic to come.

 

[bigman]

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[Aaron2345]

Soooo whos fault is that......

 

[bigman]

Soooo whos fault is that......

the guy helping me :disgust:

 

[Aaron2345]

Haha. I'm sure he won't be expecting a 12 pack in appreciation lol

 

[TwoBobsKJ]

Wow! Did the previous owner have the front shocks replaced? Or did it come that way from the factory and it just now shorted?

I've followed this thread silently but with interest - you're obviously knowledgable with electrical problems. Plus you're quite focused! ;-)

Congrats on finding the problem and the fix!

 

[Aaron2345]

Twobob. Read up top. The guy helping him find the short is at fault lol

 

[bigman]

Wow! Did the previous owner have the front shocks replaced? Or did it come that way from the factory and it just now shorted?

I've followed this thread silently but with interest - you're obviously knowledgable with electrical problems. Plus you're quite focused! ;-)

Congrats on finding the problem and the fix!

I completely left out something! :freak3:

We had installed a 3" daystar lift the weekend before. I was sure the lift installation had nothing to do with it, as we only removed the battery and battery tray.

Upon further investigation, the connector has two plastic tabs that plug into the battery tray. I did not remove the battery or that plug, so never thought anything was out of place. It was so hard to see that I dont think I would have ever found it had I not gone thru this process :yawn: