Electrical fire causes?

I apologize in advance, this is going to be a pretty long description. Hopefully someone has some experience with this and can help me out?

First, I've got a 95 with the 4.0, auto, 231.

Friday night last week I went to test drive my XJ after doing some work on the rear suspension/exhuast/driveshafts. I noticed on the drive that it felt like it had lost power and acceleration, but after shutting it off and turning it back on it felt fine. Then next morning on the road after about 50 min of driving speeds of 45-55mph the RPM's started going way up and the speed started dropping fast. Right as I pulled to the side of the road it ran ragged and then stalled. I saw a small amount of smoke seem to come from behind the dash and some from under the hood. I got out, popped the hood and watched a small electrical fire die out, about the location where the wiring for the sensors on the throttle body and CPS branch out of the wiring in the plastic rail that runs next to the valve cover. After seeing that and how melted/burned the wiring was I didn't touch anything and had it towed home.

I've now pulled it apart to trace wires and compare them to some wiring diagrams. While all the wires were burned/melted to some degree, there are a number of them which had the insulation burned clean off. Large sections, like 6" or more, and all right near each other in the bundle. I figure they were they hottest, so possibly the cause of this.

Bare wires:
Injectors- dark green w/ orange tracer (from splice where all the individual wires join towards the main harness bundle along firewall)
CPS- grey w/black tracer
CPS- orange (1 of the 3-from splice where they separate and head into the main harness along firewall)
CPS- black w/light blue tracer (from near plug to the splice)
O2- black w/light blue tracer (small section, might just have been damaged by me pulling apart the harness to inspect)

The rear engine temp sender was also broken, with the top of the sender and the plug ending up melted into the plastic rail that holds the wiring harness.

I got the section of the harness that's damaged from a 94 I plan on grafting into mine to repair it, and a full harness out of a 95 on its way to me as a spare.

My concern is that I'll go through the work of repairing the wiring just to still have the cause there (if it wasn't the wiring itself) and burn up my repair work and/or the new harness. What could cause this?

Thanks in advance
nhrocker

I don't have a lot of experience dealing with electrical fires, but I have had to track down short circuits before. Electical fires are caused by trying to run too much current through too small of a wire, which is usually caused by a short circuit from the battery to ground.

A lot of things could have caused the fire. A wire could have just been too close to the manifold, gotten hot enough to melt the insulation on a couples wires, which caused the wire, which toasted all of the other ones. You could have a short in the O2 sensor or CPS. Fuses usually prevent this kind of stuff from happening, but shit happens.

I would recommend checking for grounds when doing the repair. Just check for continuity between the wires and the ground to see if there is a ground short that should be there. You might want to check the same thing betwen the wires just to be on the safe side. If you have an FSM, it should tell you how to test the sensors with an ohmmeter to diagnose problems with those. It might also be worthwhile to look for a ground from the power distribution center under the hood. Disconnect both battery cables and see if any of the fuses have continuity (with very low resistance) with the negative batter cable. There shouldn't be.

Sorry if this isn't that much help. Electrical problems tend to suck.

Well, it's running again, sort of. Sadly I figured out what the problem is and it's something that's going to require me taking it all apart again...

As soon as I got it running I checked the area where the wiring had fried and sure enough, there's a constant stream of exhaust right there. I can't see the leak due to the air intake manifold in the way, but you can feel it as soon as you put your hand there. I already knew the exhaust manifold had a small leak where the pipes joined, it looks like there's got to be another one higher up now. Makes me wonder why I paid so much for Banks stainless steel headers... Hopefully they'll honor the "million mile warranty"

Is it the header, itself....or gasket? Keep us posted, as it helps to know about problems with products that most of us may well consider for use, at some point....

banks has a great warranty, they stand behind there stuff

XpedientJ said:

Is it the header, itself....or gasket? Keep us posted, as it helps to know about problems with products that most of us may well consider for use, at some point....

Click to expand...

Sorry I didn't update sooner, still trying to get my rig back on the road. But good news on the headers. I contacted Quadratec (where I had purchased them) and after explaining the situation they sent me a brand new set and an address to ship mine back to. Once they found the original purchase records on there end it went very smoothly compared to other returns I've tried to make in the past (with other businesses, this was my first with Quadratec)

Update on the wiring issue, it looks like the wiring to my transmission is damaged, so I'm currently trying to track that down in this thread:
http://www.naxja.org/forum/showthread.php?p=243623911#post243623911