kryptronic

This is so very true. All discussion revolves around opening up exhaust, hotter spark and more air and fuel. I've never seen a 4.0L properly tuned for performance via top end modifications. I'm sure it's been done, but I haven't seen it. Instead of properly porting the head and dealing with valve timings, it seems the answer for more power is on the bottom end by stroking the 4.0L to 4.6L or bigger. If a run-of-the-mill stroker can produce a 40% bump in HP over stock (~285HP), a properly ported and tuned head on a stroked bottom end could feasibly approach modern LS numbers (~375HP). Nobody does it because the Jeep community in general is cheap, and they get what they can with junkyard swaps and bolt-ons. Jeepers looking for that kind of performance usually put a junkyard-sourced LS in there because it's cheaper than rebuilding the 4.0L properly - with or without doing head work.

I had a clogged catalytic converter that sounded the same way under deceleration.

Chrystler lists the 'key release lever' as being available for vehicles with manual transmissions and floor shift automatic transmissions. Concerning the YJ, none were ever made with a floor shift automatic. All were column shift, and they did not have the key release lever. A large majority of YJs produced were manuals, likely accounting for the claims that all YJs had the key release lever. No automatic YJs had it. As far as Cherokees and Comanches, the lever would have been present when built on all but column shift automatics. The purpose of the lever is to provide a secondary manual safety guarding against removal of the key prior to putting the car in gear when parking.

Chrysler-era "Starfish" alloys:

Later Chrysler-era steelies:

I owned a 95 YJ 2.5L automatic without the lever. The gear selection indicator was located on the top of the column.

I've got an active post in the classifieds for sale section with a new, never installed black SMS headliner for sale.

I'm selling my MJ and a whole bunch of hard-to-find parts I've acquired over the years. I'm in York, PA, just south of the All Breeds Show, and will be willing to show the truck and/or sell parts all weekend. Please check my ad in the classifieds. I'm just posting here to let the members know who will be in town this coming weekend that I have some good stuff for sale like a D44, SWB Rollbar, AMC Black Interiors and more.

YJs with the 2.5L engine and an automatic transmission will have 3.73 ratio gearing as well, however this is a rare combo to come across.

Thanks for all the comments. I haven't had any time to drive it yet to try to produce a failure, so I'll post an update at a later date when that happens. Coil and/or distributor seem to be the most likely culprits. A couple of other things I thought about: - When the distributor was installed, I could not use the TDC mark on the harmonic balancer to find TDC. It was as if the harmonic balancer had rotated on it's own (it should be replaced - the inner seal is blowing out). I had to find TDC using cylinder one. All indications are that timing is correct. - There may be old gas in the tank. I know I put a half tank of gas in in last year, but that was on top of gas that was a couple of years old. I've only driven the truck about 70 miles over the last three years. Maybe bad unmixed gas? Probably not.

Woodbridge Jeep / Eagle / Subaru in Woodbridge, VA

Thanks for chiming in, brother. Coil is OE. Not sure if it is original to the truck (1991, 231k) or engine (1991, 140k XJ swapped unit).

I guess it's going to have to get driven. I'll take it a few places over the weekend.

The truck has now been running at idle for two hours in the driveway. The sun came out and it's hot out again - around 90 degrees. Engine temp is up around 225-230 degrees and (for the first time ever in my ownership) the aux fan has kicked on. The engine bay is hot. No signs of failure, idle is perfect... How can I go for a three mile drive one night and have a total failure to start until the next day, then have the vehicle run like a champ standing still while under vigorous conditions for hours on end? This makes no sense to me. I understand this is symptomatic of a bad coil under load, but if that were the case, I'd expect some indication of a problem by now.

I've run the truck again in the driveway at idle (800 RPM) for another hour. No variations in idle, no problems. Engine temp is steady at 220 degrees. All sensors look good via OBDI diagnostics. Under the hood is hot. The coil is hot - but no hotter than the distributor cap. I wouldn't call it excessively hot, probably normal for the conditions in the engine bay considering the load for the past hour.

Thanks for the input. The only other thing I thought to add was that I tried last night in the driveway after the tow to get it to start, and it wouldn't. It had to sit overnight before it would start this morning (see OP about that). So there was nothing that the tow job did (like rattle something loose) to fix the situation. The truck started up this evening, and I ran it for 30 minutes without issues - 20 minutes of which I had the throttle open, and the engine running at 2800 RPM. I just tried again this evening and ran it at idle for 30 more minutes, and no problems - it's running smoothly at any RPM - no variations. So in all, I've run it today in excess of 2 hours 4 different times, with the throttle at 4000 RPM for 2 minutes, with the throttle at 2800 RPM for 20 minutes. The truck started perfectly each time. The truck ran perfectly for the duration each time. It was 90 degrees in my driveway this afternoon and after running the truck the hood was hot after the 4000 RPM cycles. Hotter than it likely was last night. Engine temps have never gone above normal operating temp (~220 degrees). The distributor is not a rebuilt OEM unit, it's a generic part PPDST4696 listed under Amazon ASIN B00VVBOJT0. A bad CMP in the distributor would produce rough idle, and a bad distributor would cause misfires. A bad MAP or O2 would produce rough idle as well. I believe if the CPS was going out, I'd be having rough idle issues before a total failure. And then it wouldn't just start working perfectly again after a failure. After thinking more on it, I'm leaning towards the coil like @jdog. I have a spare on my YJ that I can borrow. I'm just not keen on paying for another $80 tow if I get it to fail, and it's not the coil.

Thank you. I replaced the entire distributor six months ago. The 'ring' is the camshaft position sensor (CMP). All good there. Properly indexed. Just ran for another 30 minutes. Temp steady at 220 degrees or so. No issues. Also ran OBDI diagnostics and found no issues. No codes. It's like last night didn't happen.

Long story short, my son in Florida is in dire need of a vehicle. As such, as much as I hate to let go of the MJ, she needs to be driven, and my son loves the truck, and will do his best to take care of it. I'm in Pennsylvania, so he's going to have to drive it 950 miles to Florida in about a week, and then intends to daily it for the next year or two. I'm pushing him to get a membership here, as it will prove invaluable to him through his ownership of the truck. Anyway, the truck has been running perfectly since some work I did to it last year. Last night I took her out to ensure everything was running tip-top. I planned a four mile circuit over hills and curves, and really pushed the truck over the first two miles. I was on the skinny pedal, shifting at high RPMs, taking corners hard, braking hard, etc. Really having some fun - and the truck ran great, until it didn't. Somewhere around mile three when I started to take it a little easier, the MJ shut off while driving, and refused to start again. When it shut off, it was traveling at 30 MPH at 2500 RPM in second gear. There was a slight surge in the RPMs to around 2800 for about half a second, then the engine shut off. I was able to pull it to the side of the road, and then it had to be towed home. I was very disappointed. I feel bad - I called it a Ford (fix or repair daily, found on road dead). While waiting for the tow, I checked a few things, and could not get it to start. It was cranking, but not starting (like a perfectly working truck with the CPS disconnected). I have gone over the fuel system 100% recently and know it's functioning as there is plenty of fuel in the rail under pressure. I swapped the fuel pump and auto shutdown relays without any change. I unplugged the O2, MAP, CPS and CMP sensors and plugged them back in just for the hell of it. This morning the truck started on the first try. It's been running in the driveway for 45 minutes and idling perfectly at around 800 RPM. No hiccups. I ran it for two minutes at 4000 RPM about 20 minutes ago and had no issues. It's still running out there. When I last maintained the vehicle, I checked compression (excellent), vacuum (excellent), fuel pressure (excellent), changed the O2 sensor and downpipe, put a new distributor (with CMP) cap and wires in, new fuel filter and fuel hose, new ballast resistor and checked/tested all sensors. OBDI scans showed no codes, no issues, all sensors reporting properly. Approximately 140K on the engine. Everything I've done to the truck is in my build thread, linked to in my signature. My thought is a bad CPS or bad ignition coil, possibly heat related. Beyond that, I have no ideas and would appreciate thoughts from the group on the situation. The truck has to do a big trip in a week and has to be reliable after that. I really don't want to fool with the hassle of replacing the CPS, so I'm looking for other ideas first.

@89 MJ: Here's a better shot of the High Output (91+) Pioneer Livery. My truck has Chief striping on the hood and header panel, so that 3/4 view isn't the best example. From the side it's all 91 Pioneer, though:

Correct - thanks for pointing that out. My 91 Pioneer had a low speed front end collision in NC prior to my ownership. It had one of the smaller factory bull bars, which protected it pretty well, but the header panel was damaged, and had to be replaced. The owner prior to me sourced the header panel on the truck from an older Comanche Chief, and got the matching hood because he liked the hood striping. The paint on the hood and header panel is a lighter silver than the rest of the truck. @SandMountainJeep: Here's a better shot of the 91 Pioneer livery. Both sides are identical.

Thanks for that. I got one from Amazon for around $35 a few months ago, and it does make a big difference. That might have been the turning point.

A bunch of stuff has happened since my last update on this build. I've been kind of distracted working on other things around here. I have done a little, though. I've been working on the tub as I get time. I stripped and blasted the underside, and fixed a busted body mount. Then I got stuck fixing a pair of holes in the floorpan. It's taken a while to get my technique down for butt welding sheet metal. I was stuck for a bit. I'm just about finished with the welding on the tub. After that's done, I'm going to cover the underside and inner tub with Chassis Saver and Monstaliner. I may have the tub back on the frame this spring, and will post a full update with pics when that's done.

Excellent. Thank you. If you need any help at all, reach out. I'm in York.

If you want to do the PowWow/Cookout at your place, that sounds awesome to me. We can schedule it there. If you're OK hosting the whole crowd for an evening, that is. I'd rather travel and help then host this year. But I'm willing to do whatever. It's your call. You can stay at my place again. No problem. Anybody that stayed at my place in 2019 is welcome to stay again. @Minuit will be here, if he can make it. That's the only person I've talked to so far about it. I guess I can count you in, too? What about Dom? Hoping he can make it again, too.

I've been looking at new Challengers lately, and recently visited the local dealer here in York, PA and test drove a T/A with a 392/T56. I almost bought it. They gave me the build sheet and it listed Zone 35 - Washington, just like the Comanche sold in VA. So, if you're interested in what the zones are, I don't think they've changed, and you can likely get the list from Chrysler, if you ask them for it. Just found this, figured the registry was a good spot for it: