Fuel & ECU Question

[gavkt 0]

Just a couple of questions. Last year I had my ECU remapped. Firstly I have been told that to get the full benefit quickly from higher octane fuels, (Tesco 99Ron) it is best to disconnect the battery and then reconnect it, so that the ECU can re learn the way the engine handles the higher octane fuel. Is this true, and if so will disconnecting my battery for any length of time affect my remmap? Apparently the ECU will learn how to handle the new fuel, but it takes a couple of tanks worth to do it.

 

Also the directional control above the heater control appears to have stopped working.

Does anyone know the cause of this and preferably a quick solution to it? As I am very short of time at the moment?

[Kevin Bacon 5]

What engine? VR6?

 

Yes I would reset the ECU if you've been using 95 previously as it will reset the knock tables. I wouldn't b'gger about with the battery though, you lose your radio settings.....just pull the ECU plug, leave it off for a couple of minutes then reconnect it. You won't lose any map information as it's stored on a chip, the reset just wipes any learned data offboard of the chip.

 

Try a search on the heater dials, it's come up many times before

[Trig 0]

If you are disconnecting the ECU to reset you should take it on a varied drive after and then hook it up to a VAG-COM after for basic settings.

[dr_mat 0]

From what I've read, just switching the ignition off and re-starting the engine will cause the ECU to go back to "0 degree ignition timing retard" and it will then continually adapt the ignition timing back from there as the engine runs and it detects knock.

The full ECU reset has other effects which may or may not benefit you.

[RW1 0]

Firstly I have been told that to get the full benefit quickly from higher octane fuels, (Tesco 99Ron) it is best to disconnect the battery and then reconnect it, so that the ECU can re learn the way the engine handles the higher octane fuel.

 

Best to leave well alone. Neither disconnecting or allowing the ECU slowly to adjust will solve your query.

 

In disconnecting, the ECU is in a rapid learn mode for 10 minutes but this only makes the car's ECU reach a driveable emission level quickly. It then settles down and continues to adjust very slowly. It will take several more hours (at least 5 hours running time) to reach somewhere near the peak settings.

 

If the ECU is left untouched, the continual adjustments will acheive just the same in a similar time.

 

In the case of the Corrado VR6, the only way is to run the engine using the same fuel (brand & grade) ALL the time and let the ECU "move" to the new settings that it's using to adjust the factory dyno map (or remapping) by.

 

Even each fuel load from the same brand & grade will vary slightly.

 

.

[gavkt 0]

Thanks guys,

It's a 92 VR6. Sorry should have mentioned that!

So according to RW1, i shouldn't do anything? A little frustrating as i can't really afford to keep running my car on more expensive fuel. Therefore if i'm not going to benifit from using a higher Octane fuel on occasion, i probably should just stick to the 95 stuff??? :?:

[ben16v 0]

gavkt, it doesnt cost much more to fill a tank with optimax or equivalent

[double-6s 0]

does it really take 5 hours to adjust the timing or whatever?

i can't notice much difference between fuels on my C vr, but on the golf vr a tank of optimax 'seemed' to have an imediate effect.

i guess it could have been psychological? just putting my foot down that much more??

[RW1 0]

does it really take 5 hours to adjust the timing or whatever?

 

It never stops (timing, lambda, temperatures etc.). Arbitary value. The driver wouldn't notice the very small increments of change. It just a continual drift one or another to meet emission requirements, performance, fuel economy.

 

can't notice much difference between fuels on my C vr,

 

Remember the situation is driven by emissions, not performance. That is what the ECU reset process is a about, returning the engine back to (as soon as possible) and then maintaining the best emission standard possible.

 

Change of petrol will change performance but the ECU will also adjust continually for the best emissions possible.

 

Therefore if i'm not going to benifit from using a higher Octane fuel on occasion, i probably should just stick to the 95 stuff???

 

Yes you will get a benefit from a tank of 98/99RON, but to get the best all round, cos of the C VR6 engine/ECU design, the fuel grade needs to be maintained at the higher octane it was designed to give the 190bhp stock power.

 

gavkt's original question was looking for a magical switch. It doesn't exist. The alternative answer to that is to look at changing the intake temperature probe reading, to change the fuelling a little. BTW, factory dyno plots show very little engine performance difference below 4,000 rpm but from own experience there is a slight change. So it depends how you want to drive the C..

 

.

[double-6s 0]

quickly?

[Kevin Bacon 5]

The alternative answer to that is to look at changing the intake temperature probe reading, to change the fuelling a little.

 

If you disconnect the intake sender, the ECU assumes and intake temp of 20 deg C, which can sometimes smooth off slight rough running....but with it disconnected you won't get optimised temperature related timing and fuel trimming.