[jlm]

I'm looking for more info on the details of this system. In particular:

what is happening at wot with respect to open loop running? does the computer use a pre-programmed fuel and timing map for this range that is not affected by the previous running conditions? Since wot conditions require a richer mixture that falls out of the range of the O2 sensor, this would seem reasonable.

is there a detonation detector that can change the timing (or anything else) and can it's sensitivity be tuned?

does anything react to override the intended throttle position, like intake temp, water temp, etc,?

[minimini36]

John

Here a few bits of information from the MCS powertrain article and another web page that was discussing the GM system used in the LS1 engine. See sections 4.2.3 for a brief description of the engine management system.
http://www.apqv05.dsl.pipex.com/m07-02-11.pdf
The reference to a torque based system means the gas pedal position is interpreted as a request for a torque value and the ECU translates this to a throttle position. In some cases this many not force the throttle wide open when the pedal is floored. Also it indicates the load or airflow is calculated based on manifold pressure and RPM as opposed to a mass airflow sensor like some cars.
Section 6.1 discusses the knock control that allows the use of 91 to 98 RON fuels with the design optimized to 98 RON.


This link also has some useful general information.
http://www.vetteguru.com/mods/howto/

"Power Enrichment Mode
When going to WOT or Power Enrichment Mode. The PCM does several things.

It no longer is concerned with maintaining economical or environmental operations. It freezes the fuel trim adjustments, stops monitoring the O2 sensors, and looks briefly where it was at in “closed loop mode”.

It then starts to rely almost exclusively on the MAF (mass airflow) sensor input for proper a/f adjustment."

Later on "In this mode the PCM will add fuel as a percentage, greater than it would normally during PE Mode, if the Ltrims are positive (correcting for a lean condition). However if the Ltrims are correcting for a rich condition (when they are negative), then the PCM will not take away any percentage of fuel that it normally adds during PE mode.

You will find that if you are running positive Ltrims during non PE mode, and you go WOT, you will see a correlating locked positive Ltrim value at WOT. On the other hand, you will see the trims locked at 0 if you normally have negative Ltrims during non WOT."

To clarify what I think he is saying. When you go to WOT the ECU adds more fuel since max power is at about 12.6 to 1 and the ECU is adjusting for 14.7 to 1 for the best tradeoff between emissions and economy. The O2 sensor switches at the 14.7 to 1 mixture point. If the long-term fuel trims are positive (correcting for a lean condition) the WOT enrichment is added to this positive fuel trim. If the long-term fuel trim is negative (correcting for a rich condition) the trim will be set to 0 and the WOT throttle enrichment is added to this value. I think this is done to avoid the possibility of going to a lean condition at WOT and doing damage to the engine. The last time I looked at my MCS the Ltrim was +5.5%. This may partly be due to the reformulated fuels required here in Phoenix that results in a slightly reduced MPG figure. The preferred condition would be a positive trim since the WOT mixture will be closer. If the trim was negative the result might be an over rich condition. The good news if you examine the graphs (2-6) showing changes in power as a function of mixture you will see changes on the rich side have less effect on power then changes on the lean side. I would think that all ECU have a similar approach to WOT. The problem is these control approaches are quite complicated and I think most of the information I have found is from individuals who have some inside information or who have spent a great deal of time reverse engineering these systems. The system used in the MINI is a Siemens EMS 2000 that is also used in several Volvos and Rovers. It uses an 80c167 16 bit microcontroller. This chip was designed for control applications such as this and includes addition hardware required for engine management. I did find an application note specifically outlining the fuel control of a F1 engine. I will see if I can find that link.