maybe another use for knock maps

[chris2712au]

Was thinking about this knock sensing and hence the other thread... Seeing it isnt really doing its job all that well... could it be used as a high low octane selection... like you have one for premium and one for E10 triggered by a switch that kind of replaced the knock sensor... Or have a mild and wild map... cause in effect it is really two complete sets of maps... as long as you could force the signal... what do you think...

[Matt]

that sounds like a really good idea. Its just a matter of disabling the knock feedback flag and then manually setting the flag which selects which set of maps to use

Now the trick is how we want to do that. Some special code is required

Perhaps TPS OFF whilst RPM = 0 to do the switch at the start. This will set/clear the flag

By default use the regular maps, but if this has been set then use the wild maps

[Matt]

if you use a resistor to replace the knock sensor then it would be permanently disabled.

if you then put a switch to short it to ground, then it will raise the knock DTC code and then use the knock maps. But I remember on CA18 it also pulled about 5 degrees extra timing too

[chris2712au]

i thought we might as well do something useful with it as people have little confidence in them working in the conventional way...

I would like to think we could turn off the feedback or have a set rpm and leave the feedback turned on just for that load point say at idle... the you trick the knock sensor... and you run off those maps till you turn the car off... well thats atleast how i thought it works... once the knock sensor goes off it runs the knock maps untill the car is restarted...

If we could do it with the type 4 board I would be loving it.... thats what i got.. also pete from plms might be interested..

[PL]

I fear it could be a tad more complex than this. Sure, we've got that DC level that the ECU likes to see so it doesn't raise a DTC.

But really what's going to be happening is the ECU will be counting knock events so it can work out whether it needs to jump to the knock maps or not. Plus as Matt mentioned, it looks like all the ECU's run a multi-stage strategy where they just jump to knock maps to start with. Then if they still reckon there's knock they'll pull even more timing. This is exactly what I saw while tuning an S14 on Saturday.

I'm not sure what they do when they raise a knock DTC. If they just jump to knock maps then your switch idea would work. If they go further and start pulling even more timing then you're screwed.

PL

[Matt]

Its definately a candidate for bench testing.

The first thing that is checked is the knock sensor input voltage is within range. If this falls out of range then the DTC code is flagged and the timing map is also flagged as used

The timing value itself if its pulled back. I thought CA18 pulled another 5 degrees on top of timing map but would need to double check each ECU on its own merrit

No knock counting etc is done when DTC is flagged so dont need to worry about that, nor firmware changes.