Originally Posted by RevCo666
Correct me if I'm wrong but would just disconnecting the battery for an extended period of time clear out the CPU on the TJ model?
Just do a google search on Chrysler PCM reset and this is discussed on MANY forums with basically the exact same discussions
I have not done it on the Jeep but have done it many times working on My 99 Durango. After disconnecting and reconnecting the battery (even after long peroids of time) the vehicle starts and runs just the same. After disconnecting the battery and turing the ignition to run for 30-45 seconds, then reconnecting the battery, it is slow to fire and idles very poorly for a brief while. Something is different.
Resetting the '97-'01 PCM - NAXJA Forums -::- North American XJ Association
This is from a post on jeep forum:
Resetting the PCM Adaptive Memory
Does this really work? From another Jeep forum:
PCM Fast Learn Mode
I think most people know that the PCM performs several functions controlling Air Fuel ratios via Injector Pulse Width and Ignition Timing.
These “outputs” are controlled using the “inputs” received from all the sensors and then comparing these reading against a set of data tables burned into the PCM.
These “memory tables” are the brains that keep the engine running at low emissions and peak economy across the RPM band
What most people don’t know is that these memory tables change. They are “adaptive”, based on sensor readings, driving habits, engine performance and sensor tolerances.
Over time, the PCM Memory Tables become tuned to your engine.
Most folks know that disconnecting the battery for 15 to 20 minutes will reset the PCM to get rid of a Check Engine Light or Error Codes stored in the PCM.
However this DOES NOT reset the Adaptive Memory Tables in the PCM. Until recently I did not know how to do this.
This procedure first came to me from the folks at Avenger. I then verified it with a phone call to a Chrysler Engineer who had called me a year or so ago to ask about my experiences with a certain part on my TJ. I figured he owned me a favor. He had to check up on this for me. He called me back a week later and did indeed verify this procedure and what it does.
To the best of my knowledge it isn’t documented in any of the FSM.
This very simple procedure will Erase the “Adaptive Memory” stored inside the TJ PCM and allow a new “Adaptive Memory” to be developed.
After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.
[L]Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.
Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”[/L]
Adaptive memory has nor been flashed, or erased from the PCM.
When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.
When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.
The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
A warm-up cycle happens when all of the following conditions exist.
Engine is running
A raise of 40F in engine temperature must occur ABOVE the engine temperature at start-up
Engine Coolant Temp must reach at least 160 F.
Once your engine has gone through 50 warm-up cycles in at least a 500-mile distance the PCM adaptive memory is set. It WILL NOT Change unless you flash it out and start all over again.
This procedure is vitally important for this installation as the install includes much larger fuel injectors and a lot more air being forced into the engine.
However I believe a lot of folks may find it useful on their won Jeeps.
Does it work?
You best performance will happen when the Adaptive memory is set to the current conditions of your engine. I tested this on the Dyno.
My test was to dyno run my Jeep after flashing the PCM and resetting the adaptive memory as I described above, with 50 warm-up cycles over a 525-mile distance.
You see the results in the charts posted above.
The last dyno run I did was performing after I flashed the PCM Adaptive Memory while on the dynamometer. We then ran the test again, using in essence the Base Setting that come in the PCM from the factory. This resulted in a loss of 9 HP and 17 ft/lbs of torque.
While this was only one test it certainly is an indicator to me of the importance of having the “Adaptive Memory” inside the PCM controlling the engine outputs based on the most current engine condition and not those set by the factory or those set in Adaptive Memory 83K miles ago.
I hope some folks will find this useful. I do believe it is a worthwhile task to do from time to time.
PS: We do not check for emissions here where I live, I would imagine if we did and if My Jeep failed I would be flashing the PCM Adaptive Memory and running the 50 warm-up cycles over 500 miles to reset things to optimum performan