Fuel injector wire shorted

[Squidmonkey]

Backstory:

1993 XJ Sport, 4.0 I6, Auto

Few days after Halloween, I was heading to the gas station to get gas, when the XJ Died. had a buddy take me to get gas (figured that I had just run out) Put five gallons into it and it wouldn't start. Had it towed home.

After further inspection, it turns out one of the fuel injector wires and rested onto the exhaust pipes and burnt through, grounding out, shutting the car down. Turns out it fried my fuel pump as well. Replaced it as well as the filter and relay. still would not start. So I did more troubleshooting and research on Naxja, and found that even though the CPS could test good, it could easily be bad and the symptoms of a bad CPS was what I was experiencing. Replaced it, still nothing. Fuel pressure, no spark. Decided to do the haynes manuel spark test. Hold a spark plug coil to ground see if it would spark, nothing. Tried using a jumper straight off the ignition coil, and tapping it to ground see if i could get a spark generated. Nothing. Went to the store, bought a new coil We where getting 12V to the coil, but nothing out of it. Nothing. Baffled. Bought a spark tester just in case the other method might not work, spark tester indicated nothing. Also, my battery was draining pretty quickly, I had figured it was in relation to us constantly trying to crank the XJ. I took a Fluke multimeter and checked resistance between Pos and Neg, with the battery unhooked. 1.2Ohms. Started pulling fuses to see if I could isolate problem. If either the I.O.D. Fuse OR the Fuse Panel fuse are removed, the short goes away. I dont have to remove both of them, just Either of them. I installed both fuses back in and then Removed Every fuse in the fuse box, not just one at a time, but all at once as well, to see if short went away. still there.

Summary:
New Fuel Pump
new Fuel Relay
New Fuel Filter
Fuel pressure at rail is good.

New CPS
New Ignition Coil

Short between Pos and Neg that only goes away when I disconnect I.O.D -OR- Fuse Box.

I'm going to check under the fuse box and see if there is anything there, but other than that, I'm completely baffled as to what I can do to get my car started again. If someone can point me in the right direction as to what to check, that would be awesome. I would normally break down into a wiring diagram and go that way, but the Haynes/Chilton ones are just not that good. What do the I.O.D. and the Fuse Box have in common that would keep my jeep from starting?

Again, i appreciate it, always seem to come through.

 

[Ecomike]

Your data does not make any sense, and must be faulty in some way. Let me explain. It sounds like you can crank the jeep, but no fuel? 1.2 ohm short between the disconnected + and - battery posts, would literally overheat and probably blow up the battery in seconds, and melt the positive post! Also it would not crank, if it had a 1.2 ohm short like you described. Are you using the ohm meter right? Battery in the meter good, probes in the right slots, dial in the right spot?

Try shorting the + and - for 2-3 seconds before measuring the ohms, to see if there is some capacitance reading a short that is not real.

Also, use the AC volts scale and check the CPS signal voltage while cranking (takes two people).

There is a small computer under the ignition coil, it and the PCM/ECU need to work to fire the coil (not just the CPS)!!!

 

[Squidmonkey]

I can fully agree that things are just odd, but I assure you, I'm using the meter correctly. I myself was completely baffled by the short.

I am getting fuel pressure now. I had to replace the fuel pump.

The jeep cranks, but will not turn over.

where is this small computer under the ignition coil you speak off? its not part of the distributor is it?

again, I appreciate all the help.

 

[Ecomike]

ICM, Ignition control module, the HV coil snaps into the top of the ICM.

Have you tested the meter to see if it is bad?

There is no way you can crank an engine, while there is separate 1.x ohm short from the positive cable to the negative cable.

If it is turning over, and has no spark it has nothing to with a purported <2 ohm short in the main battery cables. It is a missing signal to the ICM under the HV coil, or the ECU, or the CPS, or the wires in between, IMHO.

And this makes no sense? "The jeep cranks, but will not turn over." IF it cranks, it IS turning over. If the starter spins, freewheels, it is not engaging and thus NOT turning over or cranking the engine!

I have been using meters for 45 years, and I still screw up a meter reading at times, switching from ohms to volts, and sometimes forget to move the leads, or change the dial setting on mine, or find an hour later the battery was dying and giving me funky data all day!

 

[hubs97xj]

Unless Ohm's Law has changed, 12 V / 1.2 Ohms = 10 Amps.

edit- if the short fried some other components and spawned other electrical gremlins, I would be a little concerned about the condition of my PCM.

 

[Ecomike]

Unless Ohm's Law has changed, 12 V / 1.2 Ohms = 10 Amps.

edit- if the short fried some other components and spawned other electrical gremlins, I would be a little concerned about the condition of my PCM.

Good point, but so many cheap multi meters these days register near 1 ohm internal impedance for a dead short of 0 ohms, I tend think of 1 ohm as a DEAD short. Most of my digital meters read .6 ohms at best for dead short lead to lead. Also a dead short like that may have burned up the wire/short area enough to cause a little initial resistance, and the meter battery conditon is unknown...and so on. I would scared to hook the battery back up if that short was real for those reasons.

But you do have a point!!!! I have heard recently that neutrinos have violated the speed of light barrier, LOL, and been clocked traveling faster than light. :cheers:

I agree, I would concerned about the PCM, except that it is turning on the fuel pump and the starter, If I understand what the OP said (?).

 

[MAY POP]

Sounds like the portion of the PCM which fires the injectors and spark could have been fried with the burned wires. Are the injectors powered. If you can try a different PCM.
Ron

 

[Squidmonkey]

Thank you everyone for the ideas and timely responses, I do however, apologize about my delayed response, last week was rather hectic, what with food poisoning, getting OC Sprayed, thanksgiving and working incredibly late. I was not able to do much to my jeep until Sunday and this evening.

Ecomike: I have tested the meter, after I got the funky readings that was the first thing I did. I even had my buddy with me double check my readings. Baffling. Let me rephrase my statement that makes no sense then, It will crank and crank, but will not start. Apparently the 93 cherokee does not have an ICM, the ignition coil is fed straight from the ECM. Couldn't be that easy could it?

Hubs: I'm pretty sure some other electrical gremlins where created, I'm going to try and eliminate all those first

May: On Sunday I went to the junkyard and managed to find two 93's with the same engine/trans as mine. I took both ECM's out of those. I tried plugging them both in and starting the jeep, got nothing.

I have decided I should try and fix the short first as that is a problem I can see and know I can chase down.
I was able to get my hands on the drawings from a FSM and am currently studying them to find where the I.O.D fuse and the Fuse Box fuse share a common point. Apparently from the F/B (40 amp) fuse in the PDC it goes straight to the I.O.D (20 amp) fuse and then from there to Fuse 9 in the Fuse Box. According to the FMS fuse 9 is for (Radio/Clock & Memory, Courtesy Lights, Glove Box, Cargo, Dome Lamps, Telltales)
Now, Since i removed all fuses from the Fuse box and still had the short, but if I remove the I.O.D fuse the short goes away, my current assumption is that it's on the Red and Black wire going from the relay box to the F/B. I'll verify when I get another chance to work on it. The I.O.D fuse also feeds the underhood light, which I installed a few years back. I'll unplug that and see if anything changes, but I doubt it. I'm also curious if there is anything else the I.O.D fuse feeds. I'm led to this curiosity by the fact that F/B Fuse 9 is a 10 amp, and the I.O.D. is a 20 amp. Need another 10 amps for the Underhood light is just odd.

Right now the Ship I'm on is going through a major inspection, so it's looking like i wont be able to do anything until Saturday.

I'm not sure if the ECM's i got from the junkyard are good or not. I suppose the surest way for me to know is to try and find someone in San Diego with a 93 who's willing to let me put my ECM into his car and see if it works.

Anyways, I appreciate the responses. If you can come up with anymore ideas, please I'm listening. When I finally do get a chance to take a look at my car, I'll let you guys know what I find.