1996 ZJ 4.oL 2wd blows 40A Ign fuse - JeepForum.com
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Unread 12-11-2014, 06:28 PM   #1
mholmes7979
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1994 ZJ 
 
Join Date: May 2012
Location: Spring, Texas
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1996 ZJ 4.oL 2wd blows 40A Ign fuse

It's been a while since I've been on the sight so first of all thanks for all the previous help. I'm trying to help a 19 year old relative fix a fuse problem. He has little money, less knowledge & no manuals to refer to. The 40 amp IGN fuse blows either right away, a short time later or sometimes a few days later. My jeep is a 1994 so my manual is of no value. Could anyone help on a method to isolate what is blowing the 40 amp fuse? Thanks in advance for any help.

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Unread 12-11-2014, 07:22 PM   #2
Taz360ZJ
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try looking at the heated oxygen sensors wiring. there's 2 of them on a 1996, one just below the exhaust header collector in the exhaust pipe, and one just behind the catalytic converter. I wound't say common problem, but even I have fixed a few of them in my time that rubbed through on the rear drive shaft or got on the header and melted through the insulation
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Unread 12-11-2014, 07:51 PM   #3
monte350
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looking at the manual, there is a 40 amp fuse in the PDC(under the hood) that feeds the ignition switch. its fuse number 8. maybe the ignition switch has an intermittent short?
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Unread 12-11-2014, 08:21 PM   #4
ZeeJay1997
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1997 ZJ 
 
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a few things can cause this. it appears that fuse 8 is blowing and it feeds a lot of stuff. if everything else is fused correctly, it's most likely a problem in the red/white to the starter or the starter itself.

be sure the correct fuses in the other slots in the fusebox under the hood and the fusebox behind the passenger kick panel. the values are listed on the back of the covers

i posted a diagram below that shows how the circuit branches out through the ignition switch. there could be short in the dash where the wires go up the column or across the dash to the other fusebox.

i'm not sure which side of the firewall the red/white wires go through to get to the column, but i'm guessing the drivers side. if so, the harness goes all the way around front under the radiator, so if he put foglamps, mud flaps, or put any screws through up there, check that out to be sure the harness was not damaged. if they go through that side you should be able to find them in the corner near the brake booster.

with it being an intermittent short, it will be a tough nut to crack.
fuse-8pdc.jpg

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Unread 12-15-2014, 06:36 PM   #5
mholmes7979
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1994 ZJ 
 
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Thanks for the inputs. If anyone out there owns a 1996 Jeep Grand Cherokee 4.0L, 2wd, automatic I would like to ask a favor. Please check the omage reading ( right side of the ign fuse) with the ignition switch in the on/run position. Measure with the fuse removed. The left side of the fuse has 12 volts on it so you may want to put your meter on voltage first to make sure you have the right connection. The reason I need this is my meter shows anywhere from 144 ohms to 4.9 ohms depending on what relays/fuses are connected in the fuse box. My 1994 jeep has zero ohms with this same test but the 1994 & 1996 are not the same electrically and I don't really know if a 1996 should have a omage reading on there or not.

Now for a update so you won't think I've not tried other things to find out why the IGN fuse is blowing. I've unplugged the two 02 sensors, crankshaft sensor, PCM (ECU), radio, center console electronics unit under the radio. I've also disconnected every fuse & relay in the box under the hood as well as verifying all the fuses in the passenger kick panel are correct. I've confirmed that the red/wht wire going to the ignition key switch is neither shorted to ground or open. I tried only putting the IGN fuse in, then radio, then electronics module under the radio, then PCM/ECU, then all relays, then one fuse at a time. When you get about three fuses to the end the IGN fuse will blow. The fuses you add one at a time don't blow but, any combination in the last three fuses will blow the IGN fuse.

This is why I need to know the information requested in paragraph one. Once you get xxxx numbers of fuses reinstalled the IGN fuse blows. Something or a combination of things is drawing more than the 40 amp IGN fuse can handle.

Thanks in advance for any help.
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Unread 12-15-2014, 07:06 PM   #6
ZeeJay1997
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did you check the wiring to the starter?
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Unread 12-15-2014, 09:38 PM   #7
mholmes7979
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I removed the starter relay and the IGN fuse blows when the ignition key is "on" or "run" position. I never get to the start position so I doubt the starter is the problem? Am I correct?
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Unread 12-16-2014, 05:38 AM   #8
ZeeJay1997
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yes, if the relay is out, you've eliminated the starter circuit.

the difference of the circuits between the two year models is the body control module. unplug it an see if that changes anything
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Unread 12-18-2014, 04:41 PM   #9
mholmes7979
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What is & where is the body control module?
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Unread 12-18-2014, 06:12 PM   #10
ZeeJay1997
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it's under the dash near the steering column. now that i think about it, that's probably not it

i believe the thing to do at this point would be remove all fuses in both fuse boxes, and completely disconnect the battery. In the fusebox in the cab, check all fuse sockets for less than 10 ohms to ground.

it sounds like one of the wires from the ign. switch to the inside fuse box is shorted.
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Unread 12-24-2014, 07:43 AM   #11
mholmes7979
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Yup. Good plan. I ordered a service manual from Ebay & the post office lost it. Now I'll be back to trouble shooting it with no wiring diagram. I did remove all the relays/fuses from under the hood but, only checked the fuses from the inside to make sure they were correct. At this stage I'm going to disconnect the wiring hornes that goes to the ignition switch and see if I can find a connection that is grounded. If I find one I'll need to trace it down to the source. If I don't find a short to ground I'll check the ignition switch for problems. I hate working on electrical problems without a good wiring diagram.
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Unread 12-24-2014, 08:55 AM   #12
ZeeJay1997
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i have the diagrams for a 97 and they are the same, but to cover the whole system would be a massive post. if you have an inbox that will handle 10mb, pm me your email addy
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Unread 12-30-2014, 06:06 PM   #13
mholmes7979
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Thanks for volunteering the scan but, all I really need is what is behind ST-Run A21, Run-AA A31 & Run A22. If you want to try my e-mail it is mholmes7979@gmail.com. I'm not sure what the MB limit is but, I've received & sent large picture files before.
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Unread 12-30-2014, 06:52 PM   #14
ZeeJay1997
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email sent. i cannot break the specific pages out of the manual, but it never hurts to have too much information,

you may want to edit your post and take the email address out. the spambots will be blowing up your inbox.
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