Post-ECU tweak my car now better with 95 compared to 99 fuel

[Calza]

I assume you've tried this on a couple of tanks?

I.e. you didn't get a dodgy batch of Momentum or something?

[anonymous-user]

hora said:

If I used 95 or 97 it'd feel like the clutch was slipping under load.

eh?


"Clutch slipping" means the engine revs increase, but the vehicle speed doesn't. I'm pretty sure you don't mean that!


A transient roll off in engine torque, or non linearity to throttle inputs feels, well, hesitant, is the best way of describing it ;-)

[mikeyr]

How old is your car Hora?

[Otispunkmeyer]

Surely this is all just an ignition timing thing?

The timing sounds optimised for 95 but not for 97/99. The higher knock resistance of the better fuels mean you can advance the timing a bit over 95 which nets you more work done/out per power stroke.

Your car needs a knock sensor usually so that it can adjust timing to the quality of the fuel. Cars without often dont see much benefit when using higher octanes.

Or at least that is how I understood it.

[mikeyr]

hora said:

Its an 2008 (last of 05-07) 2.0R 160bhp Forester.

Ah, ok - was just curious as my "classic" Impreza Sport would occasionally have a slight hesitation which was a common thing but no one ever seemed to find a solution.

Never mind - as you were folks!

[TheEnd]

Otispunkmeyer said:

Surely this is all just an ignition timing thing?

The timing sounds optimised for 95 but not for 97/99. The higher knock resistance of the better fuels mean you can advance the timing a bit over 95 which nets you more work done/out per power stroke.

Your car needs a knock sensor usually so that it can adjust timing to the quality of the fuel. Cars without often dont see much benefit when using higher octanes.

Or at least that is how I understood it.

Yea, that's what I'm thinking, it was high advance, liked 99, but 95 and 97 would cause it to pink a little and it would pull back the timing a touch.

Now it has been lowered a little, 99 becomes average, but 95 octane is perfect and full power.

[ging84]

why does this surprise you?

chances are you were not the only person to notice the lack of power on 95 so they altered the map to improve it

[ging84]

if the issue was the knock retard was slightly too aggressive then the problem would effect any fuel, but lower octane to a greater degree
could also have something to do with long term adaptation tables for ignition timing if it has any being reset due to the software update