Stall but restart after resetting CPS

toverbey21

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99 TJ 4.0 manual. I seem to be losing communication from the Cam sensor/distributor pick up to the ECU. The jeep dies when coming to a stop or once letting off the gas to stop. I lose all gauges and get the No Bus code on the dash. i tracked down the sensor causing the issue to the cam / distributor pick up. when it stalls i can get out unplug and replug the sensor in and the jeep fires right back up. Ive done it about 5 or 6 times driving around the neighbor hood last night pretty repeatably. When at idle everything runs smooth and when shifting through the gears driving everything is fine. ive replaced both the crank position sensor and cam sensor with new mopar parts along with swapping a Napa cam sensor just to rule out a faulty sensor. Am i looking at a bad computer?
 
battery is great. no hesitation to start after the reset or trouble turning over when the asd is tripped. when running charging is 13+/- volts when looking at aftermarket voltage gauge.
 
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Reactions: Jerry Bransford
Have you tried wiggling the PCM connectors? More than a few around have had loose connections there which can cause some issues. Mine wasn’t always even registering codes.
 
ive wiggled the sensor harness/ connection thinking maybe i didnt get it connected but wasnt able to get it to shut off. ill try at the PCM tonight. im hoping for a loose connection etc. dont want to just through money at it with a new ECM and still have the issue.
 
ive wiggled the sensor harness/ connection thinking maybe i didnt get it connected but wasnt able to get it to shut off. ill try at the PCM tonight. im hoping for a loose connection etc. dont want to just through money at it with a new ECM and still have the issue.

I hope you don't have to as well, I just ordered a PCM this week and know that pain.
 
What were your symptoms if you dont mind me asking?

Mine are typical of the later model (05/06) - all 4 o2 codes (even with them the right ones and replaced recently), random stalls, etc. I’m not 100% on the fix yet, but it’s the clearest direction I have for now.

Check the diagnostics for your year in the FSM:

https://wranglertjforum.com/threads...ice-manuals-fsm-technical-documentation.4618/
Sounds to me like you may have a issue in the idling system, IAC, Map Sensor, TPS, something in there since it’s all at idle from what I read. Jerry is much more knowledgeable across all the years though.
 
Sounds to me like you may have a issue in the idling system, IAC, Map Sensor, TPS, something in there since it’s all at idle from what I read. Jerry is much more knowledgeable across all the years though.

i would think the same if everything didnt go right back to normal after resetting the cam sensor. But again, im here because i dont have the answer so who knows
 
i would think the same if everything didnt go right back to normal after resetting the cam sensor. But again, im here because i dont have the answer so who knows

I used to think this too, but for some cases - the PCM runs in open vs closed loop. Meaning, it can either run based on a preset table (e.g. during warmup before sensors are deemed to be able to provide the data) or based on all the inputs (once the sensor data is being used to make timing decisions).

The FSM does outline when each mode is typically reached, I used to think: "hey, I swapped my sensor and it's happy again" until however long later when the old symptom came back.

All that to say, I'd take a read through parts of the FSM - for me there was a lot of unknown unknowns that started to click over time.
 
Soooo got to test some stuff after getting home. started the jeep let it get up to temperature.

unplugged VSS
Uplugged Cam sensor

believe it or not everything still ran at idle and when i reved it in the garage.

pulled codes and showed both sensors unplugged. plugged everything back up and cleared codes.

found and installed the "bad" cam sensor from the original issue. reinstalled it and the jeep started and ran. pulled up and down the driveway with chopping the throttle and coming to a stop and could not replicate the stall.


while at idle i pulled and pushed on all three ecu connectors, main ground, and cam sensor harness all the way to the main harness. still could not replicate the stall.

i was the only one home and about to rain so i couldnt do any road test. Im at a loss
 
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Reactions: Blondie70
Connected/reconnected most sensors, metered everything supply/ground, cleaned battery connections, connected and reconnected PCM. so far have driven around 40 miles stopping and going and also over gravel and big rock ( to shake a connection loose) and no stall or communication loss. Sooooo ¯\_(ツ)_/¯ canceled the pcm order
 
Connected/reconnected most sensors, metered everything supply/ground, cleaned battery connections, connected and reconnected PCM. so far have driven around 40 miles stopping and going and also over gravel and big rock ( to shake a connection loose) and no stall or communication loss. Sooooo ¯\_(ツ)_/¯ canceled the pcm order

My 98 Cherokee was like that. Pull everything, test, and if you held your mouth just right when you reconnect it would be fine for months.

Ran a couple of years acting up like that but finally traced it to a slight drain on the battery from splicing by the Previous owner. Found it while changing out the motor for the tailgate lock.

If it comes back grab a multi and go over every bit of wiring you can get to.