i recently bought a dash monitor (great piece of hardware) and yesterday i saw that i was getting -ve knock correction during cruise.

i have an MY05 STi, aus/sa spec. car is completely stock, only difference is that i permanently run a 50/50 mix of 102.6L and 95UL. i do that do combat the -ve knock i was seeing across the entire rpm range on normal 95UL. since running the mix i've never seen -ve knock until now. car has done 10700km.

i did some logging last night and can replicate this problem very easily. it seems that the ecu gives -ve knock correction when the engine load is very small and throttle position in the range of 8% to 17%. this is also in any gear. anything above or below this throttle range and it's 0 or + knock correction.

what could be causing this sort of behaviour. car is very happy (AM of 16 for ages) and this is proven in the fact that i can be cruising (10% throttle, -2 KC), boot it to WOT and KC jumps up to +12.

i have logs if you need to see...

thanks,
calvin.

 

Are you running the stock aibox and filter?

I used to see 0.5 or 1.0 degree of positive correction when running a big K&N Cone Filter.
As soon as i replaced it with the standard airbox and K&N panel filter the KC value has remained at 0

 

car is completely stock - airbox, exhaust, ecu. it shows negative (-ve) KC at cruise (10% throttle) in all gears and when on WOT it goes to +12 KC which is the most the ECU can advance through KC, so the car is very happy.

just why -1.5° under cuise...quite puzzling...

 

Could be a function for emissions, NVH or fuel consumption. Subaru Owners often believe is the care is tuned for maximum power, safely. This is true, although what they dont take in to account is the fiddling that the stock ECU does to satisfy NVH, MOT, emissions and consumption "requirements". Just a thought and my 2c.

 

any guys out there more familiar with the ecu's mapping?? comments please??

its been mentioned to me by a local tuner that this has been observed on other stock cars. result is that car runs lean and egt's go very high. poor mapping by subaru??

afr's through logging seem to remain very close to stoich, but the stock lambda sensor isn't very reliable so i guess its time to fit a wideband unit and make sure..

calvin.

 

Hi Calvin

It is possible that your ECU has learned to retard in that area during a lower octane fuel batch and is just a bit slower to relearn to advance. The settings in different years/models of ECU vary considerably and the re advance learning rate may be many times the retard rate.
The later ECU's are much more active with the timing control and a 2 degree correction value (from map figure) is not a cause for concern, especially at low loads.

It could even be something as simple as a heatshield rattle or other external mechanical noise that is being picked up only at certain rpm.

Andy

 

Are you on the coast? maybe your local gas station got some J'burg 93 rubbish?? that could possibly cause it. I've noticed that my standard SA spec STi ecu allows just lean of stoich at small throttle openings and medium rpm's. (I've got a wideband to monitor) and that combination of low octane and lean will certainly give a knock or three!
Chris.

 

possible about the rubbish fuel but i doubt it. after some more quizzing of a local tuner and paul from mrt it turns out to be the following:

under the low engine load, low boost and low throttle opening the car is running its closed loop maps, its trying to get the best emissions possible. this means running high advance to burn all that fuel, which in turn means high egt's...its on the brink of det...not quite there but almost. flooring the throttle causes the ecu to switch to its open loop maps and its no longer concerned with emissions and is now concentrating on generating maximum power, which is why i see the KC of +12.

SA has no emissions control standards but because we get the same spec vehicles as AUS, which is concerned about emissions, we have to live with this downside of the stock mapping. a remap would sort it out...

 

Emission control is where a lot of aftermarket chips make their power. I.e. they disregard emissions and by doing so, allow the chip to "make more power" with the same risk / stress on the engine.

 

Calvin, you need to get rid of that front lip spoiler mate, thats the cause of all your problems


Botswana WRX, are you in Botswana?? please pop me an e-mail at gerardo at thwane .co.za