ECU Adaptation and Power Outputs

[sitas3]

A question that has been floating around my mind recently -

If an ECU is reset, and the ECU begins to adapt to the car/driving etc, then during the ECU Adaptation period (which I'm told can last for up to 3 hours of driving), will the engine's power/torque output vary considerably compared to the final 'Post Adaptation Period' power?

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[Prawn]

My understanding is that reseting the ECU will move the ignition map back to its optimum point.
As you drive the ign will <beep>/advance in response to the fuel etc you are using, however is retards a lot quicker than it advances.
If I am right (would be good if someone in the know could confirm)then as long as you are full of optimax + millers when you reset the ECU you are putting the map in the optimum place.

[sitas3]

Thanks Prawn.

so anyone else noticed this?

is it feasible to say that on a rolling road, if the ecu is reset just before the car goes on the rollers, then the power output on the rollers will vary with final power outputs on the road a couple of days later maybe?

[Andiroo]

I have noticed this at least twice now I think about it. At least I think it could be adaptation and not just better cooler airflow on the long drive home. Very hard to tell IMHO.....

Also say for example on the RR someone is logging and coding my car real-time, would I still get adaptation after this? And is adaptation always for the better?

Andiroo

[sitas3]

is adaptation better? well i suppose it depends on the logic of the tuner's code to a certain extent and also if you can ensure you are going to use the same octane fuel (probably unlikely as I bet some 'iffy' garages dilute optimax with 95 ron)

It would be great to get the full story on adaptation and its effects though. Plus I can imagine that some tuners 'Could' theoretically use adaptation to their advantage for Rolling Road before/after outputs, marketing etc..

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[Mo_S3]

Resetting the ECU...... is there another way of doing this without having to disconnect the battery for 20 mins at a time ? Can it be done by using a Vag-com ?
What about when u do a Throttle Body Adaptation ? isnt that supposed to make a big difference too to the cars overall responsiveness ?

[david7m]

Does switching between APR chip modes on an S3 class as resetting the ECU?

I've noticed that if I have an hour or so on chipped mode, then revert to standard, the pre turbo power is excellent. Not sure if this fades over the week, or if I am just getting to used to it?!?!?!?

Can the ADT's re-set the throttle bodies with there computer? Will this improve performance?

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[Dippy]

My understanding is that reseting the ECU will move the ignition map back to its optimum point.

I don't know for sure but I doubt that. I would expect that it would move to a 'safe' point which is whatever Audi set it to in order to prevent knocking with low grade fuel. Then it would try to advance the timing in order to find the optimum point for the fuel.

The reason I think this is because of the fact that knocking can cause damage. What if the engine did not <beep> quickly enough? Safetywise it is best to set the point low and let the ECU advance over time.

[DavidR]

This is a little overinclusive but may be helpful. Info provided by 'mutley' from another resource

Having read a few posts about the pros and cons of super unleaded / optimax vs standard (premium 95RON) unleaded fuel, just thought I'd elaborate on why higher octance values should be any better.

First - back to basics:

I'll assume we all know the four stroke cycle (induction, compression, ignition, exhaust) - or 'suck, squeeze, bang, blow'.

When the piston is approaching the top of its stroke during the compression phase, the fuel and air mixture is about to be ignited by the spark plug.

It is important that the mixture does not start to burn, and hence rapidly expand before the piston reaches top dead centre (TDC), otherwise the resultant burn will attempt to force the piston back the wrong way.

It is also important that the piston has not travelled too far past TDC before the burn, since this will result in wasted power.


Burn Speeds:

Contrary to popular belief, high octance fuel does not burn faster, it simply burns in a more uniform fashion. I have deliberately used the word 'burn' here instead of 'explode' - it is highly undesirable for the fuel/air mixture to explode - more on that later.

This uniform burn is very important in achieving maxium power from an engine.


Ignition Timing:

For maximum engine power (actually 'torque' at a given RPM - but same thing), it is critical that the fuel/air mixture has just started its rapid expansion in its burn phase just as the piston passes TDC.

In order to achieve this, the spark must actually initiate the burn process before the piston reaches TDC.

Since the fuel/air mixture will try to burn at a constant rate, whilst the engine will operate at different RPM, it is important to vary the point at which this spark ignition takes place, otherwise the correct piston position : burn rate would only be matched at one particular engine speed.

Engine load is also a factor, since if the piston is more reluctant to be pushed down its bore, it is desirable for the burn process to occur later in the cycle.


Octane:

The octane rating of the fuel is another way of saying 'the fuel's reluctance to explode when mixed with air'. The higher the octane, the higher this reluctance.

This is important for the following reason:

If the fuel/air mixture is ignited just before the piston reaches TDC, and the resultant rapid gas expansion cannot start to push the piston down the bore very quickly, the burn process takes place in a space smaller than a critical volume. If this happens, the burn turns into an explosion, or detonation, and the engine will exhibit a knocking noise, or 'pinking'.

The way round this is to make sure the ignition happens a bit later in the phase, so the burn takes place in a space always slightly larger than the critical volume.

This is exactly what happens when the ECU fitted to Audis detects pinking. Piezo-electric transducers are fitted to the cylinder head, often next to each combustion chamber, and they produce a voltage proportional to tiny vibrations caused by pinking. When this happens the ECU 'retards' the ignition (makes it happen later in the phase).


The Power Relationship:

If we use a fuel with a higher octane rating, we are effectively decreasing its liability to produce an explosion when the burn takes place in a space slightly smaller than the aforementioned critical volume. This is great news, since where we would have to previously <beep> the ignition, we can now leave it where it is.

The more ignition advance we have, up to a point, the more power we can extract from the engine.


The ECU Problem:

As already mentioned, the ECU's fitted to most Audis (and all turbo / s / rs versions), have the ability to 'listen' for the onset of detonation or pinking, and if detected, will <beep> the ignition slightly.

This retardation is carried out very quickly, since excessive detonation can cause severe physical damage to an engine.

Once the ignition is retarded, the ECU will 'listen' for further detonation, and if none is detected, will leave things as they are for a while.

If, over time, no detonation is detected, the ECU will tentatively advance the ignition in stages.

(Don't confuse this process with the dynamic advance / <beep> process which is initiated from the ECU's RPM / throttle position or vacuum map. The advance we are talking about here is the 'benchmark' figure which will move this whole map up or down.)

The ECU's reluctance to advance the ignition gives us our problem...


Good days / bad days:

Suppose we fuel our Audi with premium (95 octane) unleaded and go for a hard drive. If the engine has a resultant basic ignition advance caused by the use of 97/98 octance fuel, it is highly likely the ECU will detect pinking and <beep> the ignition. This will cause a drop in the power output.

Now if we fuel with optimax and go for a drive... power will NOT be restored (assume we ran the tank almost dry so there are no issues from cross-contamination)

This is because the ignition is still retarded - we could put 100 octane aviation fuel in, but without our previous ignition advance, we will still get no more power. This is the important point.


ECU Wake Up Call:

Over time, if with the previous example we used only higher octane fuel, the ignition setting will again become advanced. However, if we perform an ECU reset, the ECU performs its search for the basic ignition setting more rapidly, and we get full power restored immediately instead of sometime next week...


ECU Reset:

1. Make sure you have your radio code handy
2. Disconnect the battery for 60 secs or more
3. Reconnect the battery and turn on the ignition (don't crank it) but DO NOT touch the throttle pedal for 20 mins (this allows time for the ECU to recalibrate its drive-by-wire throttle position sensor) If you accidently touch the throttle, start again.
4. Cycle all electric windows and sunroof to allow auto calibration
5. Activate the radio
6. Go for a drive - go gently at first and slowly increase the pace up to full bore and maxium RPM
7. If you have a tiptronic then this will take a short journey to re-learn the change points to a certain extent.

(If you know where the ECU fuse is this will save bothering with the windows / radio etc.)


Summary:

High octane fuel produces no benefit unless the ignition is suitably advanced
High octane fuel does not explode faster than other fuel - its reluctance to explode is what allows an engine to yield more power
Audi ECU's <beep> ignition more quickly than they advance it again - a shortcut is to perform a reset.

[Nige_RS4]

Good post David, I would like to clarify point 3.

3. Reconnect the battery and turn on the ignition (don't crank it) but DO NOT touch the throttle pedal for 20 mins (this allows time for the ECU to recalibrate its drive-by-wire throttle position sensor) If you accidently touch the throttle, start again.

This method does apparently work, but the easiest (and most reliable) way is to carry out a TBA (throttle body adaption) using VAG-COM or via the cruise control switch on suitably-equipped APR-chipped cars. This can be very noticeable on S4's, as they seem to have a tendancy to un-calibrate themselves over time, which means you may never actually get 100% throttle, even if both feet are on the 'go' pedal. Worth doing every 3-6 months IMHO.

Nige [img]images/graemlins/thumbs.gif[/img]

[sitas3]

Thanks for the info David. [img]images/graemlins/thumbs.gif[/img]

so is the conclusion to this that you could expect a little more power for a while after resetting the ECU?

[DavidR]

Thanks for the info David. [img]images/graemlins/thumbs.gif[/img]

so is the conclusion to this that you could expect a little more power for a while after resetting the ECU?

My interpretation of what happens is that immediately after the reset, with optimal fuel, you get the optimal ignition timing and therefore optimal power. When the ECU has to adapt to inclement environmental variables it can leash in the power of the engine, and is slow to reinstate it (i.e. after a tank of 95ron) and resetting ECU gives a more perceivable increase in power as it is immediate instead of the gradual adaptation when ECU slowly advances timing to get back to the optimal position.

[DavidR]

...so yes, assuming your ECU is running retarded timing, an ECU reset will give more power, but if all environmental variables are favourable the ECU should be running optimally anyway, so no more power gained.

[wazza]

...so yes, assuming your ECU is running retarded timing

on the other hand, if the map you are resetting to on the ECU is meant for a lower grade of petrol than you have in the tank (i.e. set for 98RON, but you are running Optimax & Millers), then the power would decrease until it adapts slowly upwards. [img]images/graemlins/thumb.gif[/img]

[DavidR]

on the other hand, if the map you are resetting to on the ECU is meant for a lower grade of petrol than you have in the tank (i.e. set for 98RON, but you are running Optimax & Millers), then the power would decrease until it adapts slowly upwards. [img]images/graemlins/thumb.gif[/img]

No. The ECU will select optimal settings immediately after reset as it will fully advance ignition to these settings. So if you have 98ron it will stay advanced, if you have 95 ron it will detect the predetonation and <beep> ignition appropriately (and very quickly). The role of the reset is to kick the ECU back up to max power when you change fuel (for example).

AFAIK with regard to specific aftermarket maps (i.e. APRs 95 ron and 98 ron) the same applies. The 95 ron map will be optimal after ECU reset and will not advance to the 98ron settings (as there are programmed upper limits for ignition timing). The point of the 98 ron program is that the upper limits are altered in the reassurance that 98 ron fuel is there. Also, with the 98 ron map, the ECU is less likely to appropriately <beep> the ignition as well as stock, as it assumes user responsibility that 98 ron or above will be avaialable. APR warn not to use lower octane fuel due to potential damage caused by the high octance programs not retarding ignition quickly enough.

With all this to bear in mind, i'm not envious of tuners...