bowmanm98

It wasn't even the same Dyno. How is this going to show you anything? We all know they are calibrated differently. Can you go back to the one you did the baseline on?

JimB

So if WOT is based on a predetermined fuel map, then anyone with a more efficient intake and/or exhaust is running lean? Now that would be something worth checking on the dyno.

1999Porsche911

Not at all. The mapping will accommodate increased fuel if the computer sees that there is additional air....just like it accommodates for cooler air (more fuel), different timing (more fuel), etc.

On the opposite end...if the Maf reads less air, the fuel will be reduced at WOT regardless of the maximum mapping.

10 GT3

It is correct that o2 sensors only work in closed loop: constant speed and light acceleration. At WOT the car does run on the fuel and timing based maps. There is no O2 sensor in a production automobile that will react quickly enough for this condition. At this point it is a "best guess." The actual maps are fixed when in open loop, but that is not the end of the story. That is except for a couple changes that came along with self-learning an OBDii to improve this: these are the Alpha (base registers).

These are set in the self learning part of the ECU. Alphas are applied to the maps to modify the readings for measured running conditions. These are some of the things that are set in OBDii drive cycles. Alphas are set by accerating, crusing and decelerating at certain speeds and taking measurements off engine sensors. They are tied to the rediness monitors (part of OBDii). Once they are set, if the sensor inputs are out of range of the monitors then the ECU will re-enter self-learning mode. If it can't adjust the Alphas to correct the readings, it will start tripping codes or the rediness monitors will fail to set (showing a "not ready" or "fault" condition).

1999Porsche911

What does this have to do with a dyno run at WOT. FACT: Make a change to the airflow, air temperature, coolant temperature or altitude and the effect is immediate. Not learned, but immediate. This is why some people like to put a fan on the engine or intake or radiator so the dyno results will be higher. Do you think they make a few dozen runs so the ECU can learn that there is a fan blowing?

bnewport

So
with a K&N, the CEL is because the computer is having troubling settling the variables and not that you have a serious problem. If the computer is reset then will it learn it correctly? Is it a function of bad driving style during learning or the initial conditions being not reset?

ianwallwork

It has EVERYTHING to do with a dyno run at WOT. If you make a change to an intake that alters how the accuracy of the MAF is maintained with increasing airflow (like the K&N does with no flow straighteners for example) then the ECU will re-learn whilst in closed-loop mode. One thing it learns is how the MAF accuracy varies with airflow and these corrections are extrapolated to keep the MAF in calibration when out of the closed loop area.

You are right that it does not learn when running 'open loop' but if the extrapolated closed-loop learning mode has not been fully completed then the lambda values at WOT will not be what they will eventually be once the learning mode is completed. hence why cars pick up power over many miles after a mod is made.

So you are correct in one way - at WOT the car is running on map only with no intervention from the O2 sensors - but wrong in another. At WOT the cars run from a MODIFIED map with the miodifications being made during learning mode and extrapolated up to WOT. If you dyno before the car has re-learnt, it will run from the already-stored modified map. If there is 5% more airflow or 10degrees less temp or whatever, it will instantly use the values in the current map appropriate to the new airflow and temp. However these will not necessarily be optimum settings. What will happen over time is trhat this map will be modified and the car will eventually run on those more accurate settings.

Ian W

nycebo

That's a damn fair point.

Moreover, read this from Car and Driver.

mdillian3690

Well not sure how long it takes the computer to relearn new air intake, but my CEL has come on twice in 3 days with the K&N CAI.

1999Porsche911

Sounds all good and techy, but the fact remains that the computer does NOT calibrate the MAF in anyway. ANY and ALL changes to the MAF readings (like increased or decreased air flow) immediately effects the amount of fuel to the engine at WOT. The MAF is nothing more than a current producer that reports to the computer. At WOT, there is a specific current and that is what the computer uses for fueling.

The learning you are referring to is for closed loop ONLY. The CEL's you are getting are from closed loop ONLY. When changes in current from the MAF occur, it can take a few miles for the adjustments made by the O2 sensors to effect the LTFT. And this occurs ONLY in closed loop, not at WOT. This is the learning process. At WOT, the computer does not even look at the fuel trims so they have no negative or positive effect on performance.

mdillian3690

You you mean closed loop, is that why my CEL came on twice while idle at a red light?

1999Porsche911

The computer goes closed loop after a few minutes of warmup. Idle is the primary time for O2 sensor generated CEL's.

JimB

I'm staying out of this because it's not my area of expertise but I have to say it's a hell of a lot more interesting than posuer or income threads.

1999, my understanding of the ecu maps much closer to Ian's. Where are you getting your info? I'm not saying you're wrong because I don't know. Are you as sure that there are no "learning" adjustments at WOT as you seem to be?
Jim

1999Porsche911

I think our disagreement is between open and closed loop. Other than adjustments due to knock, there is no learning by the ECU in open loop. All learning is done in closed loop. At WOT, the ECU no longer cares what the O2 sensors or fuel trim are saying and takes it's instructions from the current from the MAF, including intake temperature and air volume. It also continues to read coolant temperature and will adjust timing accordingly.

Ever notice how much faster your car is when it is cold outside? MAF is sending more current (lower intake temp reading) to the ECU. This is telling the computer that there is nore dense air coming into the engine and it had better increase the amount of fuel to keep the A/F ratio as demanded by the map. Does your car perfom better as soon as you start driving it, or does it have to wait to "learn" that it is getting colder air?

The orginal comment made by 02 Carrera was that a change in airflow will not give you the same results at WOT as it will 2 day later. This is simply not the case with a properly functioning MAF. I really don't know what else I can say. A fact is a fact. If you are getting more air and the MAF is reporting this increase, you will get the appropriate amount of fuel increase and your power will increase immediately. Not much to learn there.