1998 4.0 stalling randomly - will refire every time - JeepForum.com
 
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post #1 of 12 Old 02-11-2020, 02:48 PM Thread Starter
8v-of-fury
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1998 4.0 stalling randomly - will refire every time

So it all started sunday morning. Started and drove fine, parked it for 4 hours while I roller skated at the roller rink and come out to just cranking, no fire.

Turn the key off and back on, listen for the fuel pump. Its priming. Still just crank, no fire. I thought what the hell, I'll give it some throttle to see if it changes anything. The 4.0 roars to life after a crank or two - weird. Drives fine rest of the day.

The next day, start it up normally and begin to clear the snow off of it. Stalls while idling. Wth, never has it ever done that before.. lean in turn key, fires right up. Runs fine rest of the day.

Today, no issues starting or driving. Except after a few minutes from the house it stumbles and stalls while trying to accelerate through town. Won't refire again without throttle. Dies once, starts and runs fine. Stumbles once more after another key cycle.

Get home, no codes. Nothing off that I can see..

I recently replaced the plugs because it was near time and it had a small miss and extended crank to start. Plugs seemed to fix those other issues.


'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
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post #2 of 12 Old 02-11-2020, 02:49 PM Thread Starter
8v-of-fury
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Kinda seems ignition related? Cause it just dies off hard. No decline and then off, just bam engines off.

It has happened hot, and stone cold. Very odd

'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
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post #3 of 12 Old 02-11-2020, 03:08 PM
jtec
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replaced plugs, tell us what brand and type.
You said no codes - how did you determine that - a scanner?

Engine Turning off, NO codes, restart without lots of cranking I would think about CKP.
Last time changed? troubleshooting vs replacing I error toward replacing CKP be sure to use a OEM component.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 12 Old 02-12-2020, 08:22 AM Thread Starter
8v-of-fury
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I do believe I used champion coppers.

Yes, determined no codes with a full read scanner.

CKP is crank position sensor? It's never been changed as far as I know. Jeep has 316k kms.

'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
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post #5 of 12 Old 02-12-2020, 09:14 AM
MrRoundel
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Well, FWIW, I had to change my CKP last year when my '98 4.0L ZJ had around 320,000 kilometers. And I think that mine outlasted those of many. I knew it was about time. And when my ZJ died while backing out of my driveway, I installed the one I had in my parts drawer.

As was suggested, and is really important, use a Mopar branded part. You really don't want to be replacing this thing anymore than once per 330k kilometers.

There are tips posted on the forum as to what extensions to use on your ratchet, etc. Pay attention and you'll only bloody a few knuckles. Good luck.

1998 Laredo 4.0L 4x4, 242 TC. Turned over 200K miles in 06/18. Original owner.
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post #6 of 12 Old 02-12-2020, 10:22 AM Thread Starter
8v-of-fury
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You'd think stalling from a loss of crank position would definitely light up a code, how primitive these things are.. lol

Odd how putting my foot in to it will cause it to catch and fire up as well.

'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
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post #7 of 12 Old 02-12-2020, 09:50 PM Thread Starter
8v-of-fury
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I just though of something I think i failed to mention, on the one stall while driving it bucked and backfired a time or two, possibly in to the intake is what it sounded like. But with both manifold being there..hard to tell really.

Is that common with a ckp failure? because is looses when it should fire the coil right?

'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
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post #8 of 12 Old 02-13-2020, 11:57 AM
terpsmandan
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An issue we had with the 98 4.0 was that on cold start, we have to cut and fill from where we park to the narrow driveway. Shifting back and forth from R to D would cause it to stall and it would be very hard to start without a lot of throttle. Never an issue cold starting, just this. We replaced the cap and rotor and now it doesn't stall. Was the cap and rotor worn just enough to cause bad contact when cold and the transmission created just enough drag when going from R to D to cause it?
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post #9 of 12 Old 02-14-2020, 11:55 AM Thread Starter
8v-of-fury
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Hmm, the cap/rotor/wires have about 45k kms on them. But I never pulled the cap to check, so I will do that.

'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
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post #10 of 12 Old 02-14-2020, 05:58 PM
F1wanab
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The crank position sensor and/cam position sensor will cause the engine to shut down, And restart as if nothing has happened.

I had this random shutdown problem and eventually traced it to the crank position sensor. No codes available via the odometer, but apparently some code readers will identify codes.

These sensors are basically proximity switches relying on magnetic fields. With time, the "perminent" magnet becomes weaker and they begin to randomly fail and recover, with increasing frequency.

When the PCM gets no crank or cam position signal, it shuts off the fuel injection. Which is why when the engine comes back to life, there's no coughing or smoke ie just like nothing ever happened.

Not sure about your misfire, perhaps a separate problem.
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post #11 of 12 Old 02-16-2020, 09:25 AM
LouC
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This is a pretty well known problem if all the sensors are good and your grounds and battery cable clamps are tight and clean, it can be bad solder joints in the engine PCM. I had this on mine back in 2012, went round and round checking things, only thing left was the PCM, had a Mopar unit installed and not one stall since.

2017 JK Unlimited Sport 6 spd
2007 WK Limited Hemi QDII
1998 ZJ Laredo 4.0 Selectrac
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post #12 of 12 Old Yesterday, 10:49 AM
MrRoundel
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A few years back my '98 let out a nice backfire when I was going a steady 50mph or so. I pulled over and thought about my 35 mile drive home after such an explosion. When I pulled the codes, a P0351 was thrown, IIRC. That pointed to a bad coil.
My coil was original on what was a 195K mile 4.0L Jeep so I replaced it with a Standard Motor Products coil. After doing so I read that this most often is the sign of a failing PCM, so I replaced the PCM with an Ebay/Junkyard unit. Not knowing for sure that my PCM was bad, I stuffed my it under my back seat for a spare. After all, I knew the car would at least run with it, as it got me home after backfiring that day. All that said, the fact that yours didn't throw a code on that backfire seems odd. Good luck.

1998 Laredo 4.0L 4x4, 242 TC. Turned over 200K miles in 06/18. Original owner.
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