Cherokee_of_Tennessee

I am at a loss here. I have a 98 XJ (my son's) and a 99 XJ(mine. Both 4wd, both 4.0 inline 6 cylinder. Mine is the one with the issue. Started out stalling on me at redlights and stop signs after heat soaking in a parking lot. The last time it did it I had to keep it going by holding the brake and keeping on the gas while stopped at redlights. Limped it home and started to work on it. I was originally not getting spark. Found the two wires coming from the pcm to the ignition coil were frayed. They were shorting together and insulation missing right at the coil connector. I replaced the coil connector and spliced wires to the original pcm wires. Now I was getting no pcm signal to the coil. Replaced the crank position sensor with a BWD from Oriellys. Tested the signal from the pcm, good to go. Let the engine run for 15-20 min with the hood closed to heat it up, then backed out of the driveway, moved from reverse to drive, and it died. Pushed it back into the garage. Did not re-start at all. Dead as a door nail. Cranked all day long, but no re-start. Checked the spark from the coil to the distributor with a spark tester light. Very weak spark. Next day, I changed the ignition coil. Re-tested for spark, all was good. Started it up, put it in reverse to back out of my garage, died again. No start, cranks all day, got plenty of spark, I have 40psi fuel pressure on the rail, I can hear the fuel pump crank and watch the pressure build after I bleed it off. I turn the key off and leave the pressure gauge on for an hour, no drop from 40psi at all. Still no start. Next I checked for spark on the plugs, all good to go. So much in fact that it knocked the crap out of me while I was holding the number one wire. So I pullled my Son's 97 XJ in the garage beside mine and started swapping parts between the two. I would take one off mine, put it on his, take the same part off his, put it on mine. His jeep never failed to start, mine always failed to start. It will crank all day, but not start. Here are the parts I swapped, but not in this order, the PCM was my last ditch attempt:
1. PCM computer, yes I did. My computer made his jeep run better than his PCM did. His pcm did nothing for my jeep.
2. Throttle position sensor
3. Manifold air pressure sensor
4. IAC valve
5. Cam shaft position Sensor
I also ohmed out all my injectors. They all read 12.7 ohms. I even checked to make sure there was a drive signal coming from the PCM to the injectors by using a circuit test light on the injector wire.
I have cleaned the Throttle body inside and out by removing it and putting it back on with new gasket and all.
I have check all grounds, all read less than 2 ohms to the negative battery cable while it is disconnected from the battery.
I had the battery tested twice by Orielly's, tested good.
I removed the upstream O2 sensor to relieve pressure on the exhaust, thinking that the CAT was stopped up. No start.
I disconnected upstream and downstream sensor separately to see if they were causing issues. No start
I took loose the hose from the air filter to see if there was an air restriction. No start.
I took loose the vacuum line that goes from the intake manifold near the map sensor to the valve cover, this seem to make it almost catch and start. It may have fired one cylinder, then quit. When it quit, it back fired in the throttle body and there was a very strong fuel smell, and a bluish white vapor rising out of the throttle body. I still had the air filter hose disconnected.
Also, there is a black fluid dripping out of the tail pipe, cant tell if it is water or oil. No smoke or anything, just seems like condensation, smells kind of like gas.
I have a veepeak obd2 reader scan tool. I don't detect any engine trouble codes. Although I get a TID $11, TID$13, and TID$16 "Manufacturer defined" error that says it has a value of zero; all under the Mode $06 on board monitoring. I cant find any definitive descriptions of these "Manufacturer defined" codes anywhere on the internet.

I am at a loss for words and open to any and all suggestions. Please respond quickly as this is my daily driver and I have spent the last 3 days from 8 am to 12 midnight each day working on this. Thanks.

Cherokee_of_Tennessee

So after it sat overnight, I get up this morning and the spark light says no spark coming from the brand new coil. I had to put jumper cables on the battery because I killed it from trying to test start it so much. Is there enough power from a jump to light up a spark light that I installed between the coil and the distributor? Or is the battery just too weak now? Anybody know?

Cummins93

If you have continuing issues that are suspect to sensors but have swapped out these sensors it's a good chance that there is some bad wiring. With a multimeter and a mightyvac you can test the map sensor output to the pcm. This is done by back probing at the sensor and back probing at the ECU. Same can be done for the tps. It is better to use an analog multimeter for the TPS.

Before you do that pull your spark plugs and check if they are drenched in fuel. I have learned the hard way that these JTEC ECUs push a large amount of fuel to start and can flood the engine quickly. Mix in a weak battery and the plugs just can't fire correctly.

A vac leak can help rule out a lazy or bad idle air control valve. You mention you created a vac leak and you got a cylinder to fire once. It's not much but it could point you in the correct direction.

4.3L XJ

After all that cranking and no start, just for giggles check your plugs. I suspect they are wet with gasoline. Might need to replace them

Cherokee_of_Tennessee

So after much frustration, finally got it to spark again. Turns out the new coil plug I put on was faulty. Took the plug out, got new wires, connected them straight to the coil without the plug, and it fired up. Now I have plenty of spark. So I let it heat up, backed it out of the driveway, put it in drive, and it FREAKING DIED AGAIN. Rolled it back down into the garage. I am thinking IAC valve. Even though I swapped it with my sons and had no effect, I swapped it when it was cold. I let the jeep sit and run for probably 20 min so it was good and hot when I backed out. I have plenty of spark now, but now no start at all, again.... Fuel pressure still rock solid. So if fuel is good, spark is good, then air has to be bad, right ?????

Edit: just also need to mention, I put another brand new coil, new iridium plugs, and new wires on today right before I found the bad coil wire plug issue.

Cummins93

Create a vac leak and see if it stalls when put in drive.

Cherokee_of_Tennessee

You made me think of another thing that happened last night. When I finally got it to start, I had forgotten to put the little hose back on its fitting on the intake. This is the hard plastic host that goes from the ccv on the back of the valve cover to the intake. So i put back where it was supposed to go, and it died. Had not problem starting back up. So i played with that for a minute. I put my finger on the little fitting on the intake, it was sucking a lot of vacuum, and when I plugged it with my finger, it wanted to stall and almost die. All I had to do was tap the hole with my finger and it would almost die. I finally put the hose back on, let it die, and it started back up with a little hesitation. Seemed to idle fine after I left the hose on before I started it back up. Don't know if that is normal or not? Still makes me think the IAC doesn't regulate air intake properly. Am I right??

Edit: Also, anybody know the standard MAP value? I have a veepeak obd2 reader and I am getting 12.7Hg. Seems high to me, but I don't know jack about that.

4.3L XJ

You are probably right

jordan96xj

On my 96, I have a vacuum of 26.7 in/hg at idle (reading taken via obd2).

Cherokee_of_Tennessee

Everyone that owns a 97 to 01 Jeep cherokee, get up right now and go look at the under side of the wire harness that runs to the passenger side of the engine and the fuel injectors in your Jeep. Mine was laying on the freaking ground stud on the back drivers side of the valve cover. And guess what? It had rubbed through the crack in the plastic corrugated conduit, and completely rubbed away the insulation from a gray wire. Not sure what this wire does, but it was grounding out and shutting down my engine. After I installed a brand new IAC Valve tonight, I still could not get it to start. Out of frustration I just started shaking the hell out of every wire harness while my son was cranking the engine. When I lifted this wire harness up, the engine fired right up with a vengeance and ran smoother than 80 year old Tennessee Whiskey on a Friday night. See the pictures for the fix I did.

I cut the wire since there was actually some strands of the copper broken, stripped back some insulaton, and installed a but splice. I wrapped some electrical tape around the splice for good measure, and to make sure there wasn't going to be any shorting from the splice to anything around it. After fixing the wire, I zip tied the entire harness up higher and away from anything I could see that might rub the wires. The only thing I couldnt really get not to rub was the harness going to the injectors. It is still touching the valve cover, but I figure it will go another 185k miles before I need to worry about that. Seems like I remember a post on here somewhere telling you to do just that, raise the entire harness up away from the hot stuff on the engine to keep it from rubbing. I guess I should have remembered it. After I got everything anchored back down good, I went for a test drive across some hard speed bumps, did some left and right 360's, and drove it hard down the highway to see if I could shake anything else loose. All is well so far. I think I will claim Victory now.

Check out the pictures below. I am serious, get up right now and go check your harnesses. If you find wires starting to fray, fix it now before you get stranded and waste 5 days of your vacation (like I did) pulling your hair out.



Frayed gray wire


Zoom in to see the bare copper on the gray wire


Location of the Harness


Another view of the wire


but splice to fix wire


see that ground stud under the harness?


Sorry for blurry pic, all zipped up and out of harm's way now

Cherokee_of_Tennessee

Well now, would ya look at this..... Schematic from my 1999 FSM manual. See the "GY", aka gray, wire??? That will shut you down quick won't it?

Cherokee_of_Tennessee

Many thanks to all who tried to help me in this endeavor. Hopefully someone will learn from this post, and not lose any knuckle skin or vacation days trying to figure it out like I did.

Cherokee_of_Tennessee

Yes OB1, I am learning to be a better JEDI now.....

Idunno

Clogged cat?

Sunshine Guy

Bad wiring, especially when it is intermittent, can be one of the toughest things to diagnose. Lack of consistency in engine behavior will drive you nuts trying to follow a logical process of elimination. You are to be commended for both your perseverance and your detective work! Congratulations.