armyofchuckness

Just for future searchers' sake, I wanted to update and say it was actually the throttle position sensor that failed. I did get a new fuel pump and strainer, and that is on the docket for replacement. Can't hurt after 160K to make sure that's freshened up. Thanks for the tips, guys!

Which old scanner did you get? I've only seen the Snap-On one that has the specific Jeep connectors. I'd spring for one at that price. As you go through the FSM to diagnose specific problems, if the problem can be diagnosed by use of a multimeter at the diagnostic port(s) it will be explained there. There is no single summary of all the tests on one page or in one chapter. If you are trying to diagnose a problem with the FSM and there's no mention of using the diagnostic port -- there's a reason. Thanks for the advice, Eagle. I thought I was losing my mind. Why show the diagram if they weren't going to show how to use it! That makes sense. Thanks again.

Thanks, guys. I'm thinking I'll swap it and the TPS out just to be sure, but I wouldn't be surprised if it's the fuel pump. Appreciate the advice. Drove it this morning, and it acted like there was absolutely nothing wrong. No hesitation. No sputtering. Weird. Better safe than sorry though. Jeep has almost 160K on the drivetrain. Wouldn't surprise me if that was what's wrong. Thanks again for the advice.

Hey, guys. I've spent the last two hours looking online for info on using a multimeter to use on the D1 and D2 connectors in my '86 2.5 liter MJ with no avail. I know that the ECU doesn't store codes. I know that Snap-On made a very expensive tool to read it. I know that you can easily test these systems with a multimeter, but I have yet to see anyone actually explain how! Even the FSM isn't particularly helpful to me. Here's what it says: There's nothing on the previous or following pages that explains this further. Do I just connect one end of the multimeter to the ground terminal at D1-3 and check for resistance everywhere else? What's "Primary circuit test (D1-2) B+ after ignition" mean? I'm sure this is all really simple and I'm asking a really dumb question here, but if there's anyone that can help out with this, it'd be really great to have this explained somewhere on the internet for posterity and the other 2.5 drivers out there. Thanks so much!

Here's the MJ: 1986 2WD 2.5 liter 4 Speed Freshly installed remanufactured long block with just over 500 miles on the clock. That last part I feel is important to the story. In early March, I spun a bearing in the old motor, but I got a killer deal on a fully remanufactured long block and did a neat-as-you-please swap out. The thing ran absolutely beautifully during the break in period. Not a problem at all. Right at the very end of that break-in period, a buddy of mine with an old Dodge pickup needed a jump start. We did a straight battery-to-battery jump (which he insisted was fine, and since he knows more about cars than I do, I didn't fight him on it). After the jump, I was driving back to work when suddenly the engine started sputtering all over the place and died. I was going about 40 MPH in third gear. I quickly turned the key and the engine fired right back up, but ran rough and continued sputtering, especially around 2000 RPM. It died two more times, but immediately fired back up. On the drive home, it sputtered, but not nearly as bad. The next day, it drove like a champ. No problems. Then it sputtered on the way home from work a little. Then it ran fine again. Then it sputtered again. Seems to do just fine under idle, but definitely presents itself most between 1500 and 3000 RPM. When it goes, it almost sounds like the engine is turning itself off more than its dying, but then it kicks itself back on, which makes me wonder... Is it electrical? I've checked all the grounding straps, the dipstick connection, etc. I even did the recommended ground strap upgrades from this forum a year ago, so I don't think it's a grounding issue. The A/C and brake light fuses blew within 24 hours of the incident, but I haven't had any issues with anything else electrical since then. No weird fluctuations in the dash lights, A/C blower, or radio. I poured through the forums, and kept running across O2 sensor symptoms sounding like this problem. Changed that out last night, and the sputtering was back in full force this morning. Other things that I've read that it could be: TPS CPS ICU Coil Distributor indexing issue (This one intrigues me, since it's a new motor with the old distributor, but it ran so strongly before the jump start.) But if it isn't electrical... Is it fuel related? I swapped the fuel filter out at the same time, just to see if that helped. It didn't. I haven't checked fuel pressure yet, but that's mostly because I don't know how. Again, I don't know if that would be a problem since I'm still pretty sure it's electrical. What do you think happened? I'm really stumped, and unfortunately, I have very little time to diagnose the issue as I'm helping my family through a bunch of issues this week, and I need the truck to get around. Any advice you can give would be greatly appreciated. I'm gonna keep looking around. Thanks for your help.

Interesting. Looks like it has a bad frame, motor, and transmission though. I was able to find a good remanufactured one locally through a friend this morning though, so I think I'll be ok. Thanks for looking!

Welp, after nearly 160,000 miles, the little engine that could just can't any more. Today I threw a bearing on the interstate and the engine is toast. It did its best to get me to a safe location before dying for good. This is my daily driver, and I really hate to part with it if I can help it. Is there anyone with an hour or so of Gainesville, Florida that has solid 2.5 liter they'd be willing to part with. The truck is a 1986 with an AX-4 manual transmission, if that helps. If you also have an AX-5 in decent shape, I would be probably be interested in that as well. Thanks so much for looking at this. It's been a really difficult day.

Yeah. I think the CPS still needs to be replaced. I'm ordering another one that will hopefully be better quality. Jeep Driver wins the diagnosis award though. I replaced the fuel injection relay and it hasn't stalled since. Thank you all for the help. I'd have been stumped otherwise, and probably spent big bucks with a mechanic trying to fix a $10 part.

Thanks for the tip, JD. Yes, it's a 2.5. I mentioned it in the post title, but I should've been more clear in the body of the post. Here's what I've established so far: A proper CPS should display .5 VAC while cranking. The replacement I got (which didn't solve the problem) pulled. .3 before I tried a mod I found on another forum and broke it. I put the old one in and it's pulling .2 VAC, so something is definitely not right there. Someone has suggested to me that it's the ECU, which I'd really rather not replace if I can help it. I don't think it's that anyway. (That's what I'll keep telling myself.) The relay is definitely a possibility. I'm sure it's a much cheaper fix than a new ECU. That would be a very difficult thing to test for failures, as it only fails for a matter of seconds. I've gotten it to repeat the scenario in three different drives. It always only happens once per drive, and it only fails for about 60 seconds at the most. Tonight, I got it started again after about ten seconds. Thanks again for the advice!

Thanks for the tip! I've got a new CPS and I'm going to swap it out and reroute the wires away from the exhaust. We'll see what happens.

Hey, guys. I'm a bit perplexed on this one. Two days in a row now my 86 MJ has done the same thing. Cruising at around 30MPH the engine cuts off. Just dies. Nothing else changes. No flickering lights. No other signs of failure. Just the engine cutting out. Both times I coasted to a stop and started cranking the engine. After two minutes of just cranking (no catch, no sputter, just the starter spinning), I'll hit it again and it immediately turns over and runs like a champ the rest of the commute home. Both times were in the evening. Both times the headlights were on. I have a full cluster and nothing on the instruments indicates any problems. I'm completely stumped. Anyone run across something like this? I've checked everything on the electrical and nothing seems to be out of place. I can't replicate it in the driveway. I've left it running in the driveway for 20 minutes. Nothing. I've driven it five times in the last two days and it's only failed twice. Any help you could offer would be greatly appreciated. Thanks!

This is really handy. Thank you! I'm hoping to one day do the same thing you're doing in my '86. Nice to see you blazing the trail with your build. Now I'm going to live in a never ending state of hope/fear that I have a late 86 firewall, although that sounds like all I need is a good hammer to make things fit.

Was that the solution? My MJ just started doing the same thing! I have a 2WD I4 with a 4speed. It starts around 35 and doesn't go away until I get back below that speed. It doesn't matter if I'm in gear or not. Turning the wheel does nothing. The vibration doesn't change pitch with speed. I just bought four brand new tires thinking that it was a balancing issue caused by improperly sized tires. (They were old and needed replacing anyway.) I was dismayed to see that it didn't solve the problem. I had to immediately leave to drive three hours to the inl-aws and had to leave the Jeep behind, so I'm stewing trying to figure out what the problem is.

Yeah, I'm a moron. All I did wrong was over tighten the cable connection at the transmission. I disconnected it, oiled the the end, and slapped it back in. Works like a champ. Thanks again, Jim.

Yeah, I hear you. I'm not a fan either. I'm restoring a '64 Valiant right now and finding gaskets for it is a pain as well. I don't like using goo if I don't have to, but I'd rather save the floor of my MJ if I can. I'm lucky I got to it before it got too bad.