I decided to try a little experiment with the scooby yesterday to see how well sainsburys Super unleaded compared with BPs ultimate unleaded.

I let the tank run to near empty and put in £20 of Sainsburys stuff.

I noticed from my SECS unit that the Knock Correction was showing 0.5 Degrees, under almost all conditions, both on boost an motorway cruising. The car did not feel a responsive as usual and this is the first time I have ever seen the Knock Correction parameter read anything other than 0.0.

Presumably for the ECU software to adjust the timing it must be sensing the presence of knock or a differing fuel mixture. Even after an ECU reset - there was no difference. There are no fault codes being shown for the car - I am convinced its down the fuel being poorer quality.

Can anyone offer me an explanation for what is happeing here? By the way, the AFR reading on a separate meter showed what it always does 15.5 - 15.6 when cruising.

Car is a lightly modded MY00 UK turbo 2000.

Comments welcomed,
TT

 

I sometimes see a reading on the KC on my SECS (03 STi PPP) but am unsure if this is in fact adding advance as was mooted on here some time ago. If the ECU is pulling back the timing, would this appear as - 0.5 for instance? Clarification on this would be appreciated.
What is the AFR reading on the SECS? 15.5 seems a tad lean? On my STi I've only seen leaner than 14.7 (stoich) on trailing throttle.
JohnD

 

Isn't positive knock correction a good thing?

I think it means your car is happier with the new fuel and is comfortable advancing ignition timing a little further (But don't go thrashing it until someone who KNOWS for sure confirms it!)

Quote ** "Presumably for the ECU software to adjust the timing it must be sensing the presence of knock or a differing fuel mixture." **

The ECU can adjust the timing (advance) based on the ABSENCE of knock too - which is what I think may have happened.

 

cheers guys, I too am confused by what is happening. Would like a good explanationi before abandoning Sainsburys totally and going back to BP Ultimate.

Hopefully the mappers and stuff will pick up the thread when they are back at work later today..

TT

 

Where in northern ireland ya from dude? my kc on my secs unit gets quite high at some points but i have knock link too and there is no det, i think it sould increase if its happy with the fuel ur using

 

+ve knock correction (KC) is good. -ve KC is bad!

the ECU has 2 ignition timing maps. the base map and the correction map. the ignition timing value shown on DD/tari/SECS is a combination of the 2.

the ECU uses the Advance Multiplier (AM) to determine how much KC is applied above the base map. the ignition correction map can go as high as 12°. typically you should see high KC mid-range and lower KC values (still +ve though) at redline.

if you're seeing -ve KC then it means the ECU is detecting knock and is pulling the timing back to prevent it breaking.

calvin.

 

I'm from Belfast - fuel bought at Sainsburys Holywood Exchange if you know it. Only 86p a litre, saving of about £6 on a full tank compared with the usual BP ultimate station I use.

Thanks for your input guys.

TT

 

TT, it would be interesting to see what happens with optimax..!

 

there are up to 6 (5? I lose track) knock correction related parameters available from the ECU, and they all convey wildly different things. From the sounds of it the SECS is displaying the learnt correction which is stored in the ECU. This can be positive or negative, or just 0. Without knowing what the other parameters are it's difficult to know exactly what's going on, although no negative numbers is going to be a good thing.

Paul