Quote:
Originally posted by JLemieux
I must take issue with all of the "Forced flashing" of the PCM that seems to be going on in this post.
For the super charger install, this is exactly what needs to be done. For all of the others doing this to their non-supercharged Jeeps, you are only making your engines run worse until the PCM has adapted the the fuel right back to where it was before you "Force flashed".
I think the piece of information that has been missed here is that adaptive learning is an ongoing process. It changes to current conditions of your engine.
If you have a cracked vacuum hose and a small vacuum leak, the O2 sensors see a short term lean condition and trims the fuel a little bit richer. This is referred to as "Short term fuel trim" or STFT. Since this cracked vacuum hose is not going to fix itself, this lean condition continues to exist and the PCM sees the O2 sensors still lean so it changes the "adaptive memory" to a richer mixture to compensate for the long term lean condition. This is call "Long term fuel trim" or LTFT.
The adaptation is different for every throttle position and load combination and is constatly being updated for current engine wear, sensor condition and any other item that will change the air/fuel ratio from where the PCM whats to see it.
So let's say you typed a 10,000 word essay on you word processor and didn't save it. On word 9,999 someone resets your computer (Forced flash). You get to type it all over again, but in the end you still have the same thing.
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Hi John,
Thanks for the post!
I think we are both saying the same things but with a slightly different understanding.
The
"Adaptive Memory" is set in the first 50 warm-up cycles that occur in anything greater then 500 miles of driving and it then DOES NOT CHANGE unless you force flush the PCM using this procedure.
Source = Project Manager Jeep PCM Engineering
Please understand I verified this 4 times with the this gentleman to make sure I understood this correctly. It is also what Avenger was telling me and that is what made me investigate. I have since validated it through a third source who dyno-tunes and reprograms most PCM's including the type in our Jeeps.
The Adaptive Memory uses as it's starting point the Volumetric Efficiency Tables which are burned into the PCM. From there it reads sensor signals and adjusts the VET over the 50 warm-up cycles to the condition of the engine.
Being the
Volumetric Efficiency Tables come into play, only during Closed Loop Modes, the O2 sensor does not enter the picture at all.
I am in full agreement and understand in your description of the
"Short Term" and "Long Term" Fuel Trim changes.
These changes are made on the fly and continuously based on the voltage (0.1 to 1.2v) sent from the O2 Sensor to the PCM indicating an A/F ratio condition, (it's actually Oxygen Content in gasses) BUT
only in Closed Loop Mode which is at Idle and Cruise Only.
The O2 Sensor signal is ignored at all other times. Source = FSM and Project Manager Jeep PCM Engineering.
Also an import fact the PCM will not go into closed loop mode until the Coolant Temp is above 160 F., further restricting when Short and Long Term Trim occur.
Here is a better picture of what is going on at a high level between the Sensors, PCM and PCM outputs concerning A/F and Timing.
The MAP and IAT sensors send Air Pressure and Air Temperature to the PCM. With that info, the PCM Calculates the Air Weight using the "Perfect Gas/Air Law" (Why? cause Air Fuel Ratio are based on weight, the weight of the Air and the Fuel).
Once the weight is determined, the PCM decided how much fuel (in weight) is needed. This comes from the Volumetric Efficiency Tables ("Adaptive Memory") when in Open Loop Mode,
OR
is calculated when in Closed Loop Mode with the help of the O2 Sensor Signal and Coolant Temp Signal.
Both "short and long term fuel trim" occurs here in Closed Loop Mode ONLY.
I am not sure I have explained that clearly, my apologies if I haven't. It has been a long day.
Have a great night. I'll be out of pocket till Sunday.
Frank
PS: I do not know what this is worth yet long term, but I have received emails and PM's from several dozen Jeeper's who have done this procedure. Every one claiming a major improment in perfromance. Guess we will have to wait and see it it holds up.