nice detailed post
1) did it ever run well after it sat if not could the gas in tank be bad/contaminated?

2) high miles the timing chain could be loose and have jumped a single tooth

 

nice detailed post
1) did it ever run well after it sat if not could the gas in tank be bad/contaminated?

Thank you. I was trying to give the full picture without being too chatty.
This is an interesting idea. I failed to mention that I did top off the gas on the wild idea that the tank was empty / the gauge was faulty. I did test the fuel pressure with a \gauge on the Schrader valve on the fuel rail literally today. The relief valve has a hose to drain excess after testing and the fuel was VERY clean & clear. Not ruled out 100%, but I feel like it is probably not the gas.

2) high miles the timing chain could be loose and have jumped a single tooth

Hmmmm. I thought about doing this when I did the cylinder head, but got a Melling-brand sprocket / gear kit + a Mopar chain and the gears just did NOT fit right. Well, they did not fit at all. I did some research and a lot of people have had issues with it. So, instead of replacing part of it, I replaced none of it. Kind of stupid, ey? Any recommendations on what brand or where to get parts? Or should I just keep the old sprockets / gears and put the new chain on?

 

is it possible you removed old chain and gears to try new ones then decided to reinstall old ones and got old chain off by a single tooth, that would make it run like crap

also dd you remove and reinstall distributor

 

is it possible you removed old chain and gears to try new ones then decided to reinstall old ones and got old chain off by a single tooth, that would make it run like crap

That would definitely be possible, although I took special care to align them, because I was trying to fix that misfire. It also does not make sense with the way the Jeep died in the middle of the street after running great for 3000 miles after the cylinder head work. I am more inclined to think the "chain jumped the sprocket tooth" theory you mentioned.

All that said, I removed all the crap in the way to get to the timing chain and it is aligned properly. If I place my credit card in the ridge on the crank sprocket and make a line to the slot on the cam sprocket, they are perfectly in line. My 6" straight edge / rule was too long, but that method suffices. There is a bit of slack in the chain (surprisingly not as much as you would think), so it might behoove me to replace it right now, just to rule it out, since I already went through all the trouble.

also dd you remove and reinstall distributor

I did remove the distributor and reinstall, being sure the rotor was aligned with Cylinder #1 TDC, per the FSM instructions.

 

Well, it turns out I did not keep the timing chain. Thought I did for some reason, but the extra chain I have is for my motorcycle. Jesus Christ. Where is my mind? At any rate, the marks are lined up and the chain is pretty tought. There are no marks on the timing chain guide / wear piece.

Since there is nothing ridiculous in there, I torqued the cam sprocket back to spec and cleaned up the old gasket mating surfaces. I will go get some new gaskets tomorrow and button everything back up.

On to the next thing someone suggests....maybe a second or third time is a charm on the distributor? I still am looking for something glaring at me, since the engine just immediately cut out. Like a bad sensor or something broken.

I read that the poor idle could be a product of the IAC going bad, but I replaced that with a Mopar OEM part in Mach 2022. When I removed it this evening to inspect, it was clean as a whistle.

 

good fuel good spark good air and mechanically sound should run

the "harmonic damper" rubber can fail and move the timing marks around

If you are near a u pull parts you could try a pcm from a xj 97 or 98 4.0 auto or 5 speed ran my 98 TJ sport 4.0 5spd on an 97 XJ 4.0 auto pcm for a couple days just to prove it would work
only issues were cruise control would not set as auto pcm interpreted the 5spd jumper replacing the park neutral switch as always in park so precluded engagement of cruise control and got a cel with code for no tcm on the ccd bus as xj auto aw4 does use a tcm

there are 8 different xj pcm part numbers that should work as a test
97 4.0 auto federal emissions
97 4.0 auto calif emissions
97 4.0 5 spd federal emissions
97 4.0 5 spd calif emissions
98 4.0 auto federal emissions
98 4.0 auto calif emissions
98 4.0 5 spd federal emissions
98 4.0 5 spd calif emissions

just avoid any xj 97 98 with VTSS module and those are pretty rare anyway

in 1999 they went from jtec to jtec+ for pcm and skim became an option also changed oil pressure sensor wiring
1996 XJ is its own strange animal as first year obd2 but still used old non bus controlled cluster
TJ just skipped 96 year model

 

good fuel good spark good air and mechanically sound should run

My thoughts exactly... very frustrating

the "harmonic damper" rubber can fail and move the timing marks around

Really?! That seems easy enough to replace. Any way to test for that?

If you are near a u pull parts you could try a pcm from a xj 97 or 98 4.0 auto or 5 speed ran my 98 TJ sport 4.0 5spd on an 97 XJ 4.0 auto pcm for a couple days just to prove it would work

Pick parts are getting so expensive these days... I might do this after I have exhausted all other options.

 

Two things stand out to me:

1. Wiring harness repairs

Usually when things go bad right after big repairs, it's something you did. Although I just went through a similar experience as yours and it turned out to be a legitimate coincidence.

-Did you confirm that the broken wires were actually for the AC clutch and the cruise?
-In what ways were the wires broken? Aged, brittle cracks or damaged from being pinched/abraded/melted/etc?
-How were they shorting? 2 wires touching? Or touching to ground?
-Neither the AC or cruise would have power in the state that you are parked (with valve cover off doing diagnostics). I guess maybe you could have left the AC/Defrost on, but not the cruise.

2. Going from no spark at all to running after simply disconnecting and reconnecting the coil.

This should not happen. Are you sure the coil is good? Sure it's not intermittent? Is that the only thing you touched at that time?

Other ideas:
-Ruling out fuel pressure is an easy thing to do. I'm sure it's not the problem, but you can rent the tool from Autozone and just remove that question.
-The computer will throw a code if it's running that bad. Sometimes it takes a long time. I would run it long enough to get some codes.
-Do you have the means to monitor the crank position sensor signal while running?
-What parts have you replaced since owning the Jeep and are they aftermarket. Like cam/crank sensors, coil, etc

It's funny how parallel our situations are. I put a new cylinder head on 9 months ago (also due to worn seats at the same mileage!), ran great, sat for a few months, then started getting misfires. Thought I had major mechanical issues due to head install, tested everything over and over and over, etc, etc. Turns out - I'm pretty sure at this point - my coil misfires when it gets hot from engine temperatures. Only 35k miles on the coil and the little bastard decided to go bad right after I did major mechanical work. Words can't describe how frustrating that is.

 

Usually when things go bad right after big repairs, it's something you did.

I totally agree with that. It is likely something I did. I would like to completely rebuild the harness, because once you start moving 25 year-old wires around, you start having problems. I have wired entire racecars in college. So, I know how to, but it is VERY hard to justify the cost of all the wires and pins, at this point.

-Did you confirm that the broken wires were actually for the AC clutch and the cruise?
-In what ways were the wires broken? Aged, brittle cracks or damaged from being pinched/abraded/melted/etc?
-How were they shorting? 2 wires touching? Or touching to ground?
-Neither the AC or cruise would have power in the state that you are parked (with valve cover off doing diagnostics). I guess maybe you could have left the AC/Defrost on, but not the cruise.

1. The damaged wires were for the IAT, IAC, and thermostat.
2. One wire had a spiral crack in the insulation, one had a chip of insulation missing (exposing the strands), and the last had a slit in the insulation (exposing the strands). None were adjacent to any other damaged wires, but I wrapped the damage in Tessa tape and plugged it back in and the issues went away. Weird.
3. I have no idea. It just went away. Not happy with that answer, tbh.
4. I did not have the A/C or cruise (obviously) on... Good point.

2. Going from no spark at all to running after simply disconnecting and reconnecting the coil.

This should not happen. Are you sure the coil is good? Sure it's not intermittent? Is that the only thing you touched at that time?

The coil resistance tests within range and it is getting / giving all the right signals now. Would a bad / intermittent coil correspond with the issue I am experiencing? It starts and runs every single time, but idles low and putters out eventually. Doesn't seem to be related to coil, does it?

-Ruling out fuel pressure is an easy thing to do. I'm sure it's not the problem, but you can rent the tool from Autozone and just remove that question.
-The computer will throw a code if it's running that bad. Sometimes it takes a long time. I would run it long enough to get some codes.
-Do you have the means to monitor the crank position sensor signal while running?
-What parts have you replaced since owning the Jeep and are they aftermarket. Like cam/crank sensors, coil, etc

1. Fuel pressure is a steady 48 psi.
2. I can do that once I put the car all back together after checking the timing chain. Just let it run and wait for a code.
3. I wish I had a scope. I do not have a means to do that. I have done a test were I back-probe the sensor and hand crank to watch for the signal to change as a tooth passes the sensor. I got results that suggested the CKS is working properly.
4. I have replaced a **** load of parts, man. Too many to count. All Mopar if available (not discontinued).

It's funny how parallel our situations are. I put a new cylinder head on 9 months ago (also due to worn seats at the same mileage!), ran great, sat for a few months, then started getting misfires. Thought I had major mechanical issues due to head install, tested everything over and over and over, etc, etc. Turns out - I'm pretty sure at this point - my coil misfires when it gets hot from engine temperatures. Only 35k miles on the coil and the little bastard decided to go bad right after I did major mechanical work. Words can't describe how frustrating that is.

That is basically the same story. Weird. Hope I can trace the issue down eventually.

 

around here
MODULE - ENGINE / POWERTRAIN CONTROL

Price $47.14 Core $7.00 Env Fee $4.71

as for balancer can compare to timing gear marks or a wood rod in spark plug hole ain't bad for getting close to TDC when hand turning but still gotta decide if TDC exhaust or compression

 

So, I put the timing chain cover back on with a new gasket. While I had the engine mostly apart, I put the thermostat in that I forgot to install during the cylinder head reinstallation. I noticed I had forgotten it after I had every thing back together and just figured i would get to it when I got to it. That was today. lol.

I decided to uninstall and reinstall the distributor, to make sure I wasn't off by a tooth or something. It took me three times to get it right, but I finally got it installed and the Jeep runs like a top! I hate the way that thing installs with having to guess what "11 o'clock" exactly is, then guessing how much to pre-spin the worm gear before installing it to get it to spin into the 11 o'clock position. Whatever. It is fixed!!

Now... I do not think this is what killed the Jeep back in March or May or whenever it was that it died. I think it was probably related to damaged wiring or grounds or something. I uninstalled the distributor a while back when diagnosing and I must've gotten wrong.

So, the answer to the question "What broke the Jeep?" is, "Heck if I know!"

The answer to "What fixed the Jeep?" is, "Uninstalling and reinstalling a bunch of bits, playing with wiring and repairing damaged wires, a new battery & spark plugs, and a bunch of time."

Comments? Thoughts?

 

with spark and fuel just about had to be mechanical and or timing nice you got it sorted and good you had a methodical/observational approach

 

Glad it's running. Hopefully it stays that way.

I would agree that it's not likely what killed it that one day, but it probably explains the poor running if you had removed/reinstalled the distributer since it first died.

 

and that little light is called a noid light, the one that goes between the spark plug lead and plug to alert when tis firing. way better than the old school way of "hey man, hold this really quickly while i turn the key"