2002 TJ 4.0 Manual Will Not Stay Running After Warming Up

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BrentTXTJ

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New member here checking in from Texas, my TJ with 104,000 has some issues that I need some help with. This all started when we where driving it would suddenly die and loose all power and would not start back up at this point it kept blowing the ASD fuse under the hood. I traced all of this back to the a few breaks in the wiring to the dreaded stud behind the valve cover and fixed all of that and still the same issue, once the jeep gets up to around 205 it will shut off and will not start back up until cooling off. At this point I replaced the crank position sensor and cam position sensor and still nothing. I went ahead then and replaced the ECM with a new one and the issue is still there. At this point I gave up on it and put it in the shop for them to trouble shoot....they ohmed out all of the wires and couldn't find anything and now they are at a loss. The Jeep is throwing a P0161 and P0121 codes currently but it hasn't always thrown these coded. The Jeep also has a new alternator on it. It will start and run fine when cold until it gets up to 205 or so and then it shuts off.

Could the issue be with a MAP sensor and the signal to the computer to go from open to closed loop? Any idea what to look at next? I'm tired of loading the parts gun and firing blindly at this thing and need my Jeep back! We have also tried unplugging the temperature sensor and no change. The crank and cam sensors where replaced with OEM Mopar sensors.

Help and thanks everyone!
 
BrentTXTJ said:
New member here checking in from Texas, my TJ with 104,000 has some issues that I need some help with. This all started when we where driving it would suddenly die and loose all power and would not start back up at this point it kept blowing the ASD fuse under the hood. I traced all of this back to the a few breaks in the wiring to the dreaded stud behind the valve cover and fixed all of that and still the same issue, once the jeep gets up to around 205 it will shut off and will not start back up until cooling off. At this point I replaced the crank position sensor and cam position sensor and still nothing. I went ahead then and replaced the ECM with a new one and the issue is still there. At this point I gave up on it and put it in the shop for them to trouble shoot....they ohmed out all of the wires and couldn't find anything and now they are at a loss. The Jeep is throwing a P0161 and P0121 codes currently but it hasn't always thrown these coded. The Jeep also has a new alternator on it. It will start and run fine when cold until it gets up to 205 or so and then it shuts off.

Could the issue be with a MAP sensor and the signal to the computer to go from open to closed loop? Any idea what to look at next? I'm tired of loading the parts gun and firing blindly at this thing and need my Jeep back! We have also tried unplugging the temperature sensor and no change. The crank and cam sensors where replaced with OEM Mopar sensors.

Help and thanks everyone!
Click to expand...

Have you tried a different coil pack?
 
The coil pack could be an issue. The heat can affect them and make them not work.

Can a coil stop working when hot?
The overheating of ignition coils can hinder their ability to conduct electricity. Wear and tear is a common reason for ignition coils failing. It causes degrading of the insulation between the primary and secondary coil windings and the primary coil. The reduction in insulation can cause the coil to overheat.
 
I verified with the shop that when the Jeep dies it is triggering the ASD relay so I'm not sure how it would be the coil with it running fine before the ASD relay triggers.
Anyone know of a good Jeep specific shop in the Houston area that could take a look?
 
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Has anybody involved to to this point actually sat down and read the FSM? There are a finite number of things that will trip the ASD and they are detailed there. An informed search will be more fruitful than blindly checking the entire harness for continuity one circuit at a time.
 
freedom_in_4low said:
Has anybody involved to to this point actually sat down and read the FSM? There are a finite number of things that will trip the ASD and they are detailed there. An informed search will be more fruitful than blindly checking the entire harness for continuity one circuit at a time.
Click to expand...

Based upon the info provided it appears the fault occurs when the system goes into closed loop, the ASD controls a number of things, but only a few that impact closed loop operation exclusively, with the O2 sensors being the primary one. That and given the fact that a P0161 code was present, looking closely at that circuitry is, if not the only logical place to start. According to the book.
 
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Painfultruth said:
Based upon the info provided it appears the fault occurs when the system goes into closed loop, the ASD controls a number of things, but only a few that impact closed loop operation exclusively, with the O2 sensors being the primary one.
Click to expand...

The shop can't figure it out, nothing they've done can be trusted at this point.

It provides power to the ignition coils, injectors, fuel pump relay, and O2 sensor heaters. If it gets de-energized it kills the whole works regardless of the fuel system status (loop).

Painfultruth said:
That and given the fact that a P0161 code was present, looking closely at that circuitry is, if not the only logical place to start. According to the book.
Click to expand...

At least for my 2006, the sensor heaters don't shut down the ASD, the ASD shuts down the heaters. The conditions listed that will cause the PCM to open the ground to the ASD relay coil are linked to the CPS and CKPS (already replaced), or the key left on with engine off (which would be detected by the absence if a CKPS signal with key in Run). He needs to figure out (or hire someone who will) whether the ASD is killing the engine or the engine is dying and the PCM is de-energizing the ASD as a result (indicating the ASD is a red herring), so he knows whether to look at things that cause the ASD to de-energize or just general things that will let the engine die. Watching the fuel system status in live data will help determine whether it's actually synchronous with hitting closed loop (mine does it well below 205) or just something getting hot.

P0121 is a TPS code. I don't know if the EFI logic has something that can overcome a bad TPS signal in open loop that falls apart in closed loop, but it's worth at least vetting out.
 
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freedom_in_4low said:
The shop can't figure it out, nothing they've done can be trusted at this point.

It provides power to the ignition coils, injectors, fuel pump relay, and O2 sensor heaters. If it gets de-energized it kills the whole works regardless of the fuel system status (loop).



At least for my 2006, the sensor heaters don't shut down the ASD, the ASD shuts down the heaters. The conditions listed that will cause the PCM to open the ground to the ASD relay coil are linked to the CPS and CKPS (already replaced), or the key left on with engine off (which would be detected by the absence if a CKPS signal with key in Run). He needs to figure out (or hire someone who will) whether the ASD is killing the engine or the engine is dying and the PCM is de-energizing the ASD as a result (indicating the ASD is a red herring), so he knows whether to look at things that cause the ASD to de-energize or just general things that will let the engine die. Watching the fuel system status in live data will help determine whether it's actually synchronous with hitting closed loop (mine does it well below 205) or just something getting hot.

P0121 is a TPS code. I don't know if the EFI logic has something that can overcome a bad TPS signal in open loop that falls apart in closed loop, but it's worth at least vetting out.
Click to expand...

He’s troubleshooting a JTEC, not an NGC.

The TPS is a passive circuit and the O2 is a reactive one. Given the over current conditions that existed, the area most likely impacted would be the reactive. Eliminate that first.
 
Painfultruth said:
He’s troubleshooting a JTEC, not an NGC.

The TPS is a passive circuit and the O2 is a reactive one. Given the over current conditions that existed, the area most likely impacted would be the reactive. Eliminate that first.
Click to expand...

Nothing I posted changed between 02 and 06...the ASD relay function looks to be a near copy and paste.

Screenshot_20231016-064524.png


I cant figure out what you're arguing against...are you disagreeing with the use of FSM-informed troubleshooting steps?
 
freedom_in_4low said:
Nothing I posted changed between 02 and 06...the ASD relay function looks to be a near copy and paste.

View attachment 465914

I cant figure out what you're arguing against...are you disagreeing with the use of FSM-informed troubleshooting steps?
Click to expand...


That is a generalized theory of operation, not actual troubleshooting steps, so yes I suppose so.

As published in the JTEC technical documentation.

“MAP Sensor Diagnostics
Listed below are the MAP sensor diagnostic routines:

• MAP voltage high: signal open or shorted to power, may be caused by a faulty upstream O2 sensor or circuit on JTEC vehicles only

• MAP voltage low: signal shorted to ground, or no 5-volt supply (No 5-volt: SBEC ONLY)

• No change in MAP voltage at start-to-run transfer (vacuum)

• No 5-volt (power) to MAP sensor (JTEC only)

• TPS Does Not Agree With MAP” - P0121 code.

It appears to me that evaluating the O2 circuitry is first, particularly given the fact that the fault is temp related. 🤷🏽‍♂️
 
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