Originally Posted by Opticon
Refering to my Turbododge days... This was true in closed loop (14.7 A/F). But since the narrowband O2 sensor couldn't read and relay the ideal range for WOT A/F (11-12), the PCM resorted to a pre-determined injector pulse calculation relative to Manifold Absolute Pressure (which was sadly replaced by MAF in our Crossfires) so a larger injector resulted in a higher volume of fuel @ WOT (to be taken advantage of by the fairly large snail shaped pinwheel toy hanging off the exhaust manifold).
Now, I have some questions I suspect has not been answered yet. But I'll ask them just in case...
Will the stock crossfire PCM adapt to larger injectors and the introduction of more air?
And what % of additional fuel and/or air can we push (or pull) into an N/A Crossfire before we exceed the stock PCM's adaptive range?
I noticed someone speculating about 20% fuel adapt in the PCM. But does the MAF have 20% of range left?
Good questions... First let me start by saying that only the NA Crossfire has just the MAF sensor, the SRT has both MAF & MAP.
The PCM is programmed to maintain the optimum air/fuel ratio. This is done by making short term corrections in the fuel injector pulse width based on the O2S output. The programmed memory acts as a self–calibration tool that the engine controller uses to compensate for variations in engine specifications, sensor tolerances and engine fatigue
over the life span of the engine. By monitoring the actual air/fuel ratio with the O2S (short term) and multiplying that with the program long term (adaptive) memory calculation, then comparing that to the limit, it can be determined whether it will pass an emissions test. If a malfunction occurs such that the PCM cannot maintain the optimum air/fuel ratio, then the MIL will be illuminated.
FUEL SYSTEM
• Fuel System Similar Conditions Window — An indicator that ’Absolute MAP When Fuel Sys Fail’ and ’RPM
When Fuel Sys Failed’ are all in the same range when the failure occurred. Indicated by switching from ’NO’
to ’YES’.
• Absolute MAP When Fuel Sys Fail — The stored MAP reading at the time of failure. Informs the user at
what engine load the failure occurred.
• Absolute MAP — A live reading of engine load to aid the user in accessing the Similar Conditions Window.
• RPM When Fuel Sys Fail — The stored RPM reading at the time of failure. Informs the user at what engine
RPM the failure occurred.
• Engine RPM — A live reading of engine RPM to aid the user in accessing the Similar Conditions Window.
• Adaptive Memory Factor — The PCM utilizes both Short Term Compensation and Long Term Adaptive to
calculate the Adaptive Memory Factor for total fuel correction.
• Upstream O2S Volts — A live reading of the Oxygen Sensor to indicate its performance. For example, stuck
lean, stuck rich, etc.
In Closed Loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other signals. In Open Loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.