ECU Compensation Factors

[bz888]

I think our R8 ECU has a Compensation Table very similar to this.
Fuel Compensation for Air Temp, Coolant Temp, Barometric Pressure etc.

Do you ever notice your car feels sluggish on a HOT day? That's because the ECU has just pushed you from the 29deg row to the 44deg row on the Map, and uses the compensation factor stored. Which reduces your power...

So, although we think Intake Air Temp and Cooling isn't important when producing max power (Rule of thumb = 10deg C equals 1% power difference), if you are on the borderline of the map, 1-2degs extra/less Air Temp can mean moving from one compensation map to another...which could be upto 5% difference in power.

Very interesting...Does anyone know much about this topic? I would love to know more about the ECU Mapping for our Bosch Motronic 9.1...

[Yspokes]

Hi,

I've been lurking since December, but since I have experience tuning OBDII cars, I have to say this would be normal. Why? Because of the different fuel grades available in the US, for one. I live in CA, the land of 91 octane premium, and I have found what you say to really apply here. Especially in the hot summer. And when I had a Dyno in my shop, I could really "see" the different mappings at work on hot days. Those of you with 93 octane available are really lucky people!

Example: Most US cars (OBDII) start up in "Open Loop", which reads only a few basic sensors while the car warms up. Then when it reaches a certain temp, it goes into "Closed Loop" which reads all of the sensors to tune the car in "real time". The most important being the intake air temp (IAT), throttle position (TPS), coolant temp sensor (in most cases, there are 2..one for the gauge, and one for the ECU, normally located in the cylinder head), and "knock" sensors, which often live in the valley under the intake, in between cylinder banks. If the ambient air is cold and dense, the knock sensors won't normally go off when you step in it unless you have crappy fuel, and the ECU will use the proper map to add fuel and timing accordingly....hence, the car runs and feels great, and is very snappy because it is getting full timing advance, and it will add fuel accordingly. If the ambient air temp is hot, and the coolant temp is hot, it is likely the knock sensors will go off because they sense detonation (PING) when you step in it (TPS), and the ECU will PULL timing advance and a little fuel (not too much fuel) to protect the pistons, and the car feels a little sluggish. So, as the ambient air temp, and octane change, the car tunes itself to get the most performance without doing any damage to itself. Most people try to get around this by using cold air induction packages, which work to some extent, but on a 100 degree day (or more here) the only way to stop this would be to use 100 octane UL fuel all the time (read:EXPENSIVE). And, humidity plays a role here too, but I won't elaborate on that at this time. So, if you've ever driven your car on a cold, dry day in the winter and had a smile on your face, now you know why.

This is basic info, and I hope it helps.

[gazza1]

OMG..We have a stalker who has been lurking:

Where have you been my man,with such excellent knowledge to share.

Please be invited to post more regularly

[Yspokes]

Greetings Mate,

I haven't posted because I don't own an R8 yet, but I'm working on it.

[SebringSilver]

Greetings Mate,

I haven't posted because I don't own an R8 yet, but I'm working on it.

That never stopped anyone else! Great info, by the way. Thanks for sharing.

[M3R8]

Good stuff and keep on posting. Good luck on getting your car, soon.

You should feel fortunate, however, since what you pay per GALLON we pay per LITER here.

With ~3.5L to the Gallon, you're doing pretty well down there

[Yspokes]

M3R8... I hear you loud and clear. When I was in London several years ago, I had to buy fuel for a rental, and my Boss was appalled. But the car guy in me appreciated the fact that European fuel is much better quality with higher octane.

SebringSilver... I followed your posts on your new wheels, and agree with the general opinion that the brushed gun metal looks great on your car!

[rawg]

Where have you been my man,with such excellent knowledge to share.

Please be invited to post more regularly

+1 and go get urself an R8...... Now!

[Yspokes]

Works for me........

[SebringSilver]

SebringSilver... I followed your posts on your new wheels, and agree with the general opinion that the brushed gun metal looks great on your car!

Thanks for the compliment!

On the topic of ECUs, and specifically ECU-tuning, I'm wondering if the V8 engine is pretty much maxed out, with Audi basically leaving very little on the table, so that even as you're moving those 1s and 0s around, the result is a very negligible amount of gains in terms of horsepower and torque.