Running GREAT then just died

Stats:

'96 XJ Country 4.0 California Emissions
5-ish inch lift, AW4

I'm having a very annoying problem right now. Yesterday I was heading out to go wheeling. Jeep was pretty loaded up, and it was warm. outside temp 96, AC blowing cold, engine temp around 220. Cruising happily down the highway at about 70 when the Jeep hitches a couple times then loses power. I get it to the breakdown lane, where it runs REALLY rough for a few seconds, then dies. Before it died, I was able to rev the engine a little, but it had a bad miss. It almost felt like my 2000 TJ with the coil packs did when it would get heat soaked. I could always clear that out, though. This just got worse until it died.

It cranks, and *wants* to start, but just never quite gets there. It'll catch for a few seconds, but it sounds REALLY rough. My '73 Dart sounds exactly like this when the float valve gets stuck and it floods.

Some things I checked. STRONG flow at the fuel rail. All fuses are good. I decided to not do any further roadside troubleshooting. A good samaritan stopped and pulled me back to town on my tow strap, and I got ahold of a friend who came and got me with his truck and trailer.

Some other things:

It had a similar problem 2 months ago on a long trip to Ridgecrest. Turned out to be a bad spark coil, but in the process of working down to that, I also changed the fuel pump and filter. They are all brand new. Knowing that new parts go bad all the time, of course the very first thing I will check is the coil, but I suspect that isn't the problem this time.

I have not yet had a chance to plug the scanner in. It's at my friend's shop right now. I'll be going over there later this morning to see if I can get it running.

I'm currently leaning toward a clogged CAT, but if anyone has any other ideas of where I should start looking, I'm all ears.

Need to check for spark and fuel first. After you see which of them you have or don't have it will be a easy fix i would think.

I found it if fires off in the morning and runs fine i would look at the coil getting hot and shutting off.Had a old truck do this to me a few times before i found it.

Cps

I'm not leaning toward CPS, since it does actually try to start. My experience with CPS is it either works or doesn't, and you either get spark or you don't. Perhaps I'm not understanding it properly, but I always thought the CPS just sent a signal to the PCM telling it to go ahead and let the spark go. It doesn't actually affect the timing. That's what the Cam Position Sensor is for. I have spark, or it wouldn't try to start.

I also checked the ASD. When I pull the relay, it just cranks; doesn't try to start. Put it back in, back to trying and failing to start. Swapped it with the AC relay. Same thing.

Did you pull a plug to see if it was flooded? Weak coil would be my guess, even being new

Have you pulled those codes yet? They're always a good starting point.

scottmcneal said:

Did you pull a plug to see if it was flooded? Weak coil would be my guess, even being new

Click to expand...

That's one of the first things I'm planning to do when I get back to my friend's shop. I'm also going to buy a basic tune-up kit on the way over. Cap, rotor, plugs, wires. Stuff that needs to be done anyway.

But yes, I'm going to look at the coil first. Luckily, we have no less than 3 other XJ's over there, all '99s, which have the same coil as mine. I'll swap one and see if anything changes. Can't hurt.

Of course, the troubleshooter in me says IF it is the new coil, then something else is causing it to fail prematurely. So even though that may be the cause of the engine not starting, I'll still have to figure out what's killing the coil.

1. Install all tuneup hardware. Failure to do so can result in chasing of your tail.

2. Test or swap ignition coil

3. Can't tell for sure about fuel delivery unless you test. WITH A GAUGE. For a 96, you need 49 psi, plus or minus 5 psi at the rail for the engine to start. You can test without the engine being started.

4. While the crank sensor usually fails catastrophically, it doesn't always fail that way.

1. Install all tuneup hardware. Failure to do so can result in chasing of your tail.

2. Simple check for spark would be a good idea. Remove a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground. Have a buddy crank the engine while you watch. You are looking for a strong, BLUE, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine, which would lead you to step #3.

3. Test or swap ignition coil

4. Can't tell for sure about fuel delivery unless you test. WITH A GAUGE. For a 96, you need 49 psi, plus or minus 5 psi at the rail for the engine to start. You can test without the engine being started.

5. While the crank sensor usually fails catastrophically, it doesn't always fail that way.

Hey, I have a 94 Cherokee with the 2.5 and it did the same thing yesterday. Ran fine, then died on me after it sputtered and ran rough before finally quitting. Then i went back to it later and it started right up. Got it home, changed cap/rotor/wires/coil and took it for a test drive. Ran better but still had a small miss that I have been fighting for a little while. But then it quit again. So I let it cool and it refired but ran rough. So questions are:1) Crank positioning sensor cause this problem? I got codes 11,12,14,54,and55. 2)if it is the CPS, could that cause the miss I am fighting? 3) am hearing that the CPS is a hard item to get through Mopar. Is that true, and if it is does anyone think NAPA would have a decent part or is there an aftermarket CPS that someone would suggest?

Check CPS wiring, my old 89 had a bunk wire right near the connector, on days when it was warm out, if I would drive 10+ miles, turn the car off to go get some dinner or something I would come out, and it wouldn't start. Got to the point where I would just open up the hood, turn it over, shake the wires, and repeat until it started. After about 6 mos I took about 2" off CPS and harness wire, put a new connector on, and ran fine until transmission died 75K miles later.

Just an FYI, sputtering was never a symptom of the CPS wiring failure.

My CPS gets heat soaked and then the jeep shuts off. It does the same act like it wants to start gig, then cools off and fires right up.

I know it's the CPS because I can pour a bottle of water on it and the jeep starts. Not a recommended fix for long trail rides in the summer.

They aren't always an on/off switch.

ok, well, after 6 hours of throwing parts at it, it runs, better than ever (and it ran great before).

After sitting overnight, it still wouldn't run. I plugged my scanner in and watched all the parameters (I have a good Snap-On scanner that gives me everything). It showed that I was getting all the right signals, but still nothing.

I put on all the tune up parts (I would have done it anyway....it really needed it), but still nothing. As I pulled out the old plugs, I noticed that they were all gapped at .070..TWICE the OEM spec. Sure, it ran, but that's hard on the coil and other ignition components. But still, nothing.

Next I decided to test my clogged cat theory, and cut it out with the sawzall. Nothing, but I'm glad I cut it out, because it's badly rusted. I planned to buy one through work...er....go to a qualified repair shop and purchase it and have it installed by them....yeah...that's my story, and I'm sticking to it. Stupid California.

Anyway...

We pulled out the FSM and read up on the PCM start-up routine. After going through the checklist, I plugged the scanner back in and noticed something I should have noticed right off: The injectors weren't firing. Hmmmm....

So I went back and looked again, but all the right signals were coming in (yes, including the CPS and Cam Sensor). However, I went ahead and changed the CPS with a new one from CarQuest, and...

It fired right up. Weird. I understand that the CPS can get flakey, but it's very, very strange that I could SEE the signal coming in yet it wasn't working. I'm guessing that it's a combination signal, and something wasn't right. At any rate, it got a great tune-up, and now runs.

Here's what I think caused my problem, and my earlier failed coil: About a year ago, I overheated BAD. So bad that the engine heat-siezed. I fixed my cooling issues, and it ran great. I felt lucky. However, I think the massive heat soak stressed my solid state components that were attached to the engine. That put me on borrowed time, and this summer finally caught up to me.

The good side is that I have basically at this point replaced every system on the Jeep over the last year and it should (hopefully) become reliable again. Time will tell.