aerocorey

What's it worth? That's pretty subjective. It's up to you and what your skills are. I wouldn't pay a damn thing for a unibody truck with rust in the rockers, but I spent more than a year looking for my truck and paid waaaay too much for it. Maybe you can do body work or just don't mind the rust, but you're still looking at a truck with an ignition problem that someone else has already given up on. On that truck the usual gremlin is the crank position sensor. Some guys get them to run by unplugging them and plugging them back in. Could be the coil, could be any number of things. The fact that it wouldn't rev before it stopped working makes me wonder, but I'm not the guy to break down what that could mean. Mine is clean and supposedly ran great, and I've been chasing an intermittant no-start for a week now. Right now I'd swap it straight across for a rusted out truck with a bad CPS in a heartbeat. Wouldn't it be great if you get it for like $500, unplug the CPS, plug it back in, then drive it away?

If I had to take a guess at the police package, it's probably just something like a slightly stronger chain.

231 can't be driven on dry pavement in 4H or 4L because it forces the front and rear driveshaft to rotate at the same speed. Imagine that you were rolling the Jeep around in a parking lot with the transfer case in neutral and the CAD locked. When cornering, the front and rear driveshafts want to rotate at diferent speeds because each wheel is rotating at a different speed. The differential in the front and rear axles allow for the different wheel speeds on each axle, but the result is that each differential produces a slightly different driveshaft rotation than the other. When driving a 231 in anything other than 2H the front and rear driveshafts are mechanically locked at the same speed. This results in the wheel hop felt during cornering in 4H or 4L on a dry surface with a 231. The outside front wheel is hopping to keep up with the inside front wheel in during the turn because the tires want to rotate at a diferent speed than they're being allowed. This binding is harmful to your driveline. 242 allows the front and rear driveshafts to slip some during normal operation so it can be left engaged on dry pavement without binding the driveline, thus leading some people to describe it as AWD rather than 4WD. If there's no viscous coupler in a 242 how does it operate? 229 is chain operated, but the chain is driven by a viscous coupler. 228 uses a mechanical differential to drive the chain, but they suck because all it takes is 1 wheel with no traction to get the whole thing stuck. I had a Grand Cherokee with a 249, also chain driven with a viscous coupling. The old FSJ Quadra-Trac used a bunch uf clutch packs to drive the chain, but it was still chain driven.

There's a port in the side of the throttle body right above where the MAP sensor gets its vacuum. What is it?

Doesn't start at all, no spark whatsoever. If I went out there now it would probably start because it's been sitting. Once I start it and shut it back off it's a crap shoot whether it'll start back up or not. I can crank it for 2 seconds, 10 seconds, 20 seconds...no spark. Doesn't seem to matter how long I run it before I shut it off either, it decides when it wants to not start. If it doesn't start I can walk away from it for 15 minutes, then it'll fire right up. I used it to drive from OH to VT last week. It ran on the highway without stopping through each tank of gas, then sat dead at each fuel pump for 15 minutes before it would start again and drive through the next tank of gas. I see how that ballast resistor could make it stall after it's started. I do have good fuel pressure all the time though. I did replace the fuel filter just for good measure. I also thought I hit the jackpot earlier when I found the wiring for the cam sensor chafing on the engine block, but when I inspected it there was no damage and a good layer of electrical tape wrapping. I zip tied it in a better place just because it was there to be done. That was about 5 seconds before the previously mentioned roll start. Is this one stumping you guys yet like it is me?

I didn't do anything with the puel pump ballast resistor. Should I? When it doesn't start it cranks just fine, meaning that the starter engages and the engine turns over but there's no spark at the coil. Fuel pressure is good, just no spark. When I roll started it, yes, I just got it rolling and popped the clutch, sooo whatever was keeping it from starting wasn't enough to keep it from running once started. Ignition switch? It cranks fine so I doubt it. Starter relay? It cranks fine so I doubt it. Next time it does this I'll test for 12V at the wire that runs from the starter relay to the ECU for 12V, but the problem isn't that there's improper advance in the spark during cranking, it's no spark whatsoever during cranking. I've tried tapping this during cranking as well. ECU? I don't know a damn thing about them except that they apparently don't fail very often. Cam sensor? Don't know how to test it, would probably just replace the distributer and cross my fingers. Would love someone to tell me how to test this beast.

I've replaced the battery cables, added a battery to chassis ground, replaced the ignition module, checked for 12V at the ignition module on the occasions it won't start (it checks good, I was testing the wrong yellow wire before), had the battery load tested, and even tried tapping the ECU with the toe of my boot when it won't start. Nothing has changed. Today it did it while I was facing downhill in a driveway. It was running fine and I shut it off to go in the house. I came out 5 minutes later and it wouldn't start, just cranked and cranked and cranked. It roll started like a champ. I still haven't checked the cam sensor because I don't have any procedures for checking it. The parts store in town doesn't even list that sensor. I don't see it on the diagram in my crappy book, but I do see a "sync sensor" that I don't know anything about. Is that the cam sensor? I guess I'd have to replace the whole distributer if it's bad. Which of the sensors on this thing have the power to keep the engine from starting? Will it keep running if any of them stop working while the engine is running? I had a Dakota once with a bad CPS. If it couldn't make contact with the CPS while it was off it wouldn't start, but if it lost contact while it was running it wouldn't stop until i turned it off. I realize this is a diferent system, and I've already replaced the CPS, but it makes me wonder. Other than the cam position sensor I'm still out of ideas other than the starter relay and the ECU.

I messed with it again. There's a chance that I'm a retard. There's 2 yellow wires going into the ignition module. I think I tested the wrong one.

...or maybe not. I finally got the truck to not start in a place where I had someone who could crank it for me while I play with the multimeter. With the key in ON and START there was just under 5V at the yellow wire going into the ignition module. That wouldn't be odd on some vehicles, but I don't see on the diagram if there's a resistance wire between the ignition switch and the ignition module on this truck. If it's supposed to be 12V I'll just have to find the resistance that's not supposed to be there and eliminate it.

Springfield

Eagle, thanks. I'm familiar with the different systems and what years they were used, but I'm clearly still a rookie at troubleshooting them. I thought the book I'm using referred to the ECU as an ECM. My bad. Honestly I find it confusing that the folks at Renix would name the ignition module as an ignition module. It seems to me to be little more than a giant socket for the coil to sit in. I'm sure my incorrect nomenclature is doing the same thing to you guys. I've replaced the CPS and inspected the wiring as suggested previously. The old CPS cheked good and the wiring was zip-tied away from the manifold. The new CPS is routed the same. I don't see how the cam position sensor could create the intermittant problem I'm having, but just because I don't see it doesn't mean it's not the problem. From what I see on the diagram I have the only 2 components in the system that care whether the key is in ON or START are the starter relay and the ECU. The starter relay is woking properly because the engine is cranking. I'm going to replace the battery cables and add a battery to chassis ground before anything else. If that doesn't fix it what would you suggest next? I'm running out of ideas.

Messed with it some more and looked at the diagrams. I wasn't able to get the truck to not start all day today, so I didn't get much troubleshooting done. Looking at the diagram makes me think the ECM does most of the work I've come to think of an ignition module doing. Seems like the ignition module isn't anything more than a socket that the coil plugs into on this truck. does it really ever go bad? The ignition module gets 12V to the same pin straight from the ignition switch during cranking and running. The signal for advancing timing during cranking goes to the PCM. If the no-start happens again I'll test for 12V during cranking at the ignition module. If it's not there I'll check wiring, maybe replace the ignition switch. If there's 12V at the ignition module I'll check for 12V at the correct pin on the ECM plug. If there's 12V there I suppose I should try a new PCM. Thoughts? Please?

Are you referring to the magnetic trigger wheel in the dostributer? No, I haven't yet. I don't really suspect that as the problem because when it runs it runs well. It doesn't die. It just won't start again for 30 minutes after I shut it off. Am I overlooking something about the way the trigger wheel operates? I'm honestly a little confused about what a trigger wheel would actually do since there's a crank sensor. Does it just compare the crank and cam position for the ECM to provide more accurate timing information to keep things running smoothly as the timing set wears? I haven't really looked at the wiring diagrams too hard yet, but on a Wagoneer there are 2 seperate logic pathways for cranking and running. If these trucks are like that too I wonder if the cranking circut in the module has problems switching properly when the module is hot. There's an ECM on this too, right? I almost suspect that an ECM on this would do more of the work that I'm associating in my head with the ICM on a Wagoneer. This learning curve is killing me. I've finally landed for a few weeks on my road trip so I'll bust out the mulitmeter and start shooting wires tomorrow. I need to make sure the cranking voltage is making it to where it needs to. I've also given the starter relay a few taps, but I didn't figure that would do much since it always cranks, just doesn't light off. I'd love it if someone could point me to some better online diagrams.

I've been having an intermittant no start. When it runs it does fine, but when you shut it off it won't start again unless you let it sit for 30 minutes or so. I've been into full size Wagoneers for awhile now, and if this happened on a Wag I would have replaced the ignition module in a heartbeat. I got some good suggestions on here saying I should start with a CPS and then try a coil. I've replaced the CPS, coil, cap and rotor, and I've tested and inspected the plugs and wires. It's still happening. Other than battery cables and grounds all I can think of that's left to try is the module. I borrowed a spark tester and I'm not making spark at the coil. The battery cables don't look great, but all the accessories work fine, it cranks, and when it runs it goes until I shut it off. I'm not making a weak spark, I'm naking no spark at all. Is the module a waste of time? It's killing me that I haven't replaced it already, but that's alot of money.

Replaced the air filter, fuel filter, cap, and rotor. Much better starting. We'll see if it fails me again...

$#!&!!! I just started it and shut it off a few times to mess with the heater. Now it won't start. :headpop:

You may want to check your vacuum supply reservoir. It's that football looking thing behind the front bumper on the passenger side. It controls quite a bit of the heater controls that require vacuum. :cheers: That ball is making vacuum, no leaks. The heater doors work fine. Oizarod115 says that valve defaults open, so that means it would require vacuum to be closed. That makes sense since my last MJ had no vacuum to the heater controls but I still had a hot defroster. Seems to me that I've got 2 problems... 1. The valve has failed, and it's stuck closed. 2. My heater control panel isn't porting vacuum to the valve when I turn the heat off. If I can free up the valve so it operates smoothly and get the vacuum porting from the heater controls correctly I'll leave it like it is. If not I'll replace the valve with a "T" fitting so it works all the time. There's no A/C in the truck so it won't hurt anything. I'll just go through the vacuum lines behind the heater controls real good to be sure nothing is leaking. Looks to me like that valve's only job is to eventually fail and make my heat stop working.

No cracks in it, in fact it looks pretty good. It never really failed the tests with a multimeter that my Haynes book says to run either, but it just made sense that the coil would cause the problem. I've only run it for a day since replacing it. Watch it die on me again later today just to be spiteful because I think I've got it fixed...

Replaced the coil today. Haven't had it happen since I replaced it.

I'm not as worried about the valve as I am curious why the hose that goes to it never makes vacuum. I'll get the heat blowing hot one way or the other. I like to leave things stock if I can so I'll probably look at the back of the heater panel in the cab when I mess with it tomorrow.

My wife bought my current MJ while I was stationed overseas. Now I'm back and we were moving a bunch of stuff from UT to VT. I rented a tow dolley and threw the MJ behind my Grand Wagoneer and we set off on the trip. Yesterday my Wag's timing went out on the highway just west of Toledo. We took the MJ off it's trailer and I drove it into town. I haden't had a chance to do much of anything with this MJ before yesterday, but she came through. I hadn't checked any of the fluids or inspected anything on the truck, just fired it up and drove like hell. We got the Wag stored safely and I finished up my road trip in the MJ. We're in NY at the in-laws now, pressing on to VT tomorrow. I'm sad to see my Wag gone, but I guess this is my MJ's time to shine.

Is this valve supposed to get vacuum to pull it open or vacuum to pull it closed? Mine isn't getting vacuum and my heat blows cold. I'm gonna tinker with it tomorrow. I can't get the little vacuum hose going to it to make vacuum no matter what position the heater switch is in. If I can't get it working right I'm either going to wire it open or replace that whole section with a "T" fitting.

That was going to be my next guess at it. I can't imagine changing that CPS in a parking lot :eek: KUDOS to you... :cheers: they aren't THAT bad... a 1/4" drive wobble socket and a few foot long extension its a 20 minute job. (of course working above your head is always better than working on your back) Sooo, you're telling me that when you're at a hotel you have enough 1/4" extensions on you to get the ratchet clear of the transmission. Wow, you are prepared. Seriously, it wasn't that bad. I'd rather have done it on a lift, not in february, and not with a glovebox toolkit, but it wasn't that bad. Like 3 seconds after I asked for help figuring out the coil connector I realized I was looking at the coil mount and that the coil pops out of it. I ran the tests in the book, it checks good. Maybe I should start the truck for a few minutes and test it again.

Pulled the coil to put a multimeter on it. I have a Haynes book. The picture in the book doesn't match the plug on my coil. Can anyone talk me through what each terminal is?

Thanks for the replies. I do recall now from the last time I had an MJ that the CPS is a known weak link. Changing it in a hotel parking lot was the least fun I've ever had in a hotel parking lot. It also didn't fix the problem. :wall: I'm probably not going to mess with it anymore this week. I'm towing the MJ from UT to VT behind my Grand Wag. We're rolling out tomorrow morning. If I can get this problem licked we're planning to ship this truck overseas next month with us. I still haven't done the plugs and wires and crap, so I'm not freaking out just yet. Guess I now have a spare CPS. Any other suggestions are welcome. What's wierd is that when it's running it never dies. It waits until I shut it off, then it just won't start. Seems like if I give it an hour or so it's ready to start again. Vacuum stuff all looks good. Maybe a bad coil?