Getting my head around fuelling and mapping...

[Darren S]

I'm wondering if the tech bods can answer this scenario for me?

Car A - Standard 182, fed a tankful of 95RON petrol once a week for say, 6 months. ECU mapped to 98RON.

Car B - Standard 182, fed a tankful of 98RON petrol once a week for say, 6 months. ECU mapped to 98RON.

All other factors being the same (driving style, same mileage, etc) how does Car A handle the crappier spec petrol? Does the ECU take into account the fact that it's being fed skimmed-unleaded and try it's best with timing, retardation, etc to maximise the usage of the 95RON?

What would happen at the end of the 6 month period if the cars swapped their types of petrol? Would Car A happily adapt to the new 98RON which is what it was optimised for in the first place? And would Car B's ECU throw a hissy-fit being downgraded to 95RON after using 98RON for so long?

Cheers,
D.

 

[Fred@BTM]

the earth would come to an end, your engine will blow up, and you might cry

 

[Batman]

damn the world would come to an end? may have to try that

seriously your engine would blow? it better not as i wanna start usin 98ron

 

[Darren S]

LOL! :rasp:

Ok, it was a spazzy question, but I just wanted to know what the answer would be. You hear so many conflicting stories and opinions, that the geek in me just needed to know the truth. The whole truth, and nothing but the truth.

D.

 

[BenR]

Both would be fine once the short term trim tables have adapted to the new fuel.

Either way in the clio, the fuel makes very little difference.

 

[Darren S]

Both would be fine once the short term trim tables have adapted to the new fuel.

Either way in the clio, the fuel makes very little difference.

Cheers Ben. Could the tables be adjusted in a short time, such as a single tank of petrol? Or would it change gradually over time?

D.

 

[John D]

Think it would take at least a couple of tanks to adjust. Maybe dependent on how hard the car was driven (?)

 

[fmp_]

its called a knock sensor. stops running lean on lesser fuels etc.

hence why u can run 95 (i have most of the cars life) or run something like 101 ron without worry.

 

[stan*]

The ecu uses the knock sensor to r****d ign. It will liekly detect det on lower octane fuel sooner, and so lower advance. On higher it will not det so soon, so will allow more advance.

 

[BenR]

It'll only adjust the areas where it feels abnormal combustion. So going from 98 to 95 it might not have to 'adjust' the trims that much. When it senses a pink or so it will knock back the ignition at that point by a set amount, usually 3 deg. It will then over a period of crank revolutions try to advance the ignition again by tiny increments until it pinks again, where it will back it off once again and set a trim value.

Going from 95-98 will be the same as the ecu will periodically advance the ignition to 'see' where it can set longterm trim tables.