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2000 4.0 XJ dies randomly while driving

DinoXJ

NAXJA Forum User
Location
OREGON
This has happened three times now and almost a fourth. The first time I was going 20 mph and it died. The gauge cluster and all other electrical systems stayed functional, the RPMs just dropped to 0 and I had no power. I pulled over, placed into park and it started right back up. About three weeks later (yesterday) I was getting onto the freeway and while accelerating on the on-ramp it died, same as before. Gauge cluster and other electrical worked, RPMs dropped to 0, no power. I pull over and put into park, only this time it doesn't crank right over. I wait a minute and then it starts no problem. I get at most 30 seconds down the road and it happens again. This time I was able to start it again immediately. I drive for 10 minutes to get home with no issues. Today when I was driving to auto parts store with OBD logging info the timing advance for #1 cylinder went from 7-40 range to negative 60 and RPMs dropped for a moment but didn't die. The log also shows the speed going from 0 mph to 140 mph when the incident occurred. No check engine light or codes any of the times it happened. There was no sputtering or choking, it just went from normal operating conditions to no power.

2000 XJ I6 with auto tranny (rebuilt 14 months ago) and 190k miles

Troubleshooting:
- Checked fuel pressure at the rail with a pressure test gauge. With key on and engine off pressure was ~46 psi. It might of gone up slightly when I turned engine on, but didn’t appear to. I turned engine off and pressure dropped to ~42 psi after 15 minutes.
- Checked cable for crankshaft position sensor, all clean and look good
- While idling I tapped the CPS with a hammer lightly and the Jeep didn't die


My main concern is this happening and me being in the middle of the freeway so I want to try to get ahead of this if at all possible. My suspicion is the CPS but I don’t know how to know that for sure. Is there any way to know if a CPS is going bad but isn't all the way dead yet? Are there any other possibilities than the CPS or fuel pump? Could it be the computer, and if so is there a way to test for that?

Any help is appreciated. Thank you.
 
The CPS is the most common and most logical sensor to suspect when there is random stalling. The CPS can be tested but may not test as faulty until it is hot. 150 - 175,000 miles is often when the CPS decides to go.
 
Got one on order from Amazon. It's a Mopar part as it sounds like the aftermarket ones are all crap. I'll update when I have it replaced. It apparently takes about 3 feet of extensions to access it... this should be fun
 
In my experience, when a CPS quits, due to heat, it takes a while for the CPS to cool off before it will restart.
They have never restarted immediately.
 
In my experience, when a CPS quits, due to heat, it takes a while for the CPS to cool off before it will restart.
They have never restarted immediately.

Mine would restart immediately in the beginning. Then it got to the point where I would literally wait for a minute. Then a couple minutes. Then going home about a week later almost did not make it.
 
Mine would restart immediately in the beginning. Then it got to the point where I would literally wait for a minute. Then a couple minutes. Then going home about a week later almost did not make it.

Only a week from first instance until it would barely restart? How long before it shit the bed?
 
Only a week from first instance until it would barely restart? How long before it shit the bed?

Never let it get that far. In the beginning it would stall as soon as I reached operating temperature but would restarts immediately. Might stall again 1/4 mile down the road or let me get to where I was going. Kinda of a crapshoot on that. Then it got to the point where it would take a minute or so to restart. Then one day leaving work, live a 1/2 mile away, it did not even get up to operating temp and stalled. Finally got it restarted, then stalled again. Thought I was dead in the water but finally got her started again and got home. Now in the drive she behaved better. But she never left the driveway until I put in the new CPS. I pushed my luck far enough at that point. LOL.

Oh and never really was sure it was the CPS. I tried the resistance test but it came back as good. I checked the wiring and it looked OK. Never actually but a fuel pressure gauge on her but it was just dying like you turned off the key. No sputtering so figured it was not fuel related. Obviously I was getting spark sometimes. No wonky gauges, no No Bus thing, no codes or pending codes. All the other things I read that could be associated with a Bad CPS. But went for it anyway and to frank got lucky that is what it was.
 
Good news for me. I was able to find a Mopar CPS on Amazon for ~$85. Then, the shop I had the tranny rebuilt at decided to replace it for free (labor) even though it was already past the 1-year warranty. Turns out they did in fact use an aftermarket CPS.

After a few days of driving with the new CPS, no problems.
Thanks all for the input.
 
In my experience, when a CPS quits, due to heat, it takes a while for the CPS to cool off before it will restart.
They have never restarted immediately.

Just went through this issue and this is the exact symptom. I'm trying to find the thread that helped me but have had no luck so far. I have a 97 with a new 4.7 stroker. Same thing would happen, it would take me 20-30 min before I could restart the jeep. I thought at first it was a vapor lock issue since I've seen 2 stroke boat motors seem to have the exact same issue in very hot weather.

Long story short it was the cps. Cheap sensor but a little difficult to replace.
 
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