Petrol Octane Change - Would it cause this...?

[j_richards123]

Hi All,
I usually run my car on Shell V Power simply beacuse ive noticed the fuel consumption is better and seems to run better on the stuff.

Yesterday the level was low and the wife filled the car yesterday with regular 95 unleaded. I was on the M25 yesterday afternoon and the car didnt seem to run as smooth as usual and almost seemed a bit hesitant at times.

The question is, would it be possible that the timing is adjusting to the different fuel here or am I looking at something more? The car seemed to running fine before.

By the way the car is B7 A4 1.8T

Cheers

[RobCrezz]

I think your car does have a knock sensor, so yes it would be more hesitant on 95RON. Its likely that the ECU has detected knock and retarded the timing to protect the engine, the result is less power.

Use up all the 95RON as low to empty as possible and refill with Super. Run it for another 10 miles or so then reset the ECU.

[j_richards123]

I suspected this might the case, cheers mate!

It shouldnt take too long to dispose of the 95 stuff

[Marf]

j_richards123 said:

It shouldnt take too long to dispose of the 95 stuff

But it will likely take a long while for the ECU to advance the ignition timing back to where it was when you were running on VPower.

[sinizter]

Marf said:

But it will likely take a long while for the ECU to advance the ignition timing back to where it was when you were running on VPower.

Really ? How long would you expect it to take ? I have heard 3 tanks, but personal experience proves otherwise.

On my old BMW it was very quick.

The difference was almost instantly noticeable when I went from a tank of 95 to better, when it was close to empty.

[5lab]

you'll probably only notice any difference on full throttle openings. on light openings, if its hesitating, the problem is elsewhere

[RobCrezz]

Marf said:

But it will likely take a long while for the ECU to advance the ignition timing back to where it was when you were running on VPower.

Yeah, once your sure all the 95 is gone, reset the ECU.

[j_richards123]

Surely doesnt the ECU reset itself?

I am not too sure if the "manual" reset (or at least I wasnt aware or is it just a case taking the negetive terminal off the battery and refitting after a few minutes or is it a VAG COM thing..?

[RobCrezz]

j_richards123 said:

Surely doesnt the ECU reset itself?

I am not too sure if the "manual" reset (or at least I wasnt aware or is it just a case taking the negetive terminal off the battery and refitting after a few minutes or is it a VAG COM thing..?

Most cars you can either pull a fuse, or like you say, remove the negative terminal for a little while.