Hi there,

i talked to someone tonight about fuel and timing interpolation between the high and low map.
He told me that there is a mut value where you can log, the percentage of interpolation. 100% = high map, 0% = low map, 50% = (high+low)/2.

But i don't remember the names or mut codes, he mentioned.

I found "octan value" on evoscan, but i m not sure what it is.

It was all about 90550001 rom. But the mut values should be same to all roms, because he referred to the orginal mitsu mut logger, i don't have access to.

Maybe someone knows what i have heard there.

I don't know what terms i should use for searching. And if its just one value for both maps, or if there is a value for each map set.

thx Jan

 

Hi - the octane value in evoscan is the number representing the interpolation between Hi and Low octane maps.

 

Agreed. The guy I go to for all my tuning advice and help uses the octane number and AFR's for tuning. While on the dyno we set both maps to the same values then once tuning is complete and safe we adjust the low maps to have a very safe margin for error.

Josh

 

These notes below is how I think it works, based on lots of evom reading.
Some aspects may not be right, but the dissasemblers can comment/correct as required. I have not seen any info on fuel map interpolation if different.



S3-KNOCK SUM, OCTANE NUMBER & MAP INTERPOLATION

These three functions are the parameters which combine to give the final ignition timing value, operating temperature aside.

In the short term, the timing will be reduced directly, based on the KNOCK SUM. In some parts of the map, a knock count of 1-2 will cause a -1° of timing. Other parts of the map, where the engine is not producing peak torque, it may take a count of 3 to get a -1° reduction in timing.

The octane ‘number’, which is used to control the ignition timing shift from the HI-OCTANE map to the LO-OCTANE map, starts off at a value of 255 or 100%. Not quite an arbitrary number, as its value would have an affect on the driving time it would take to transit from fully Hi to fully LO-OCTANE map operation (for a given rate of knock). The following equation describes the method for deriving the new ignition timing from the two timing maps:

(((255 -octane#) x LO-MAP) + (octane# x HI-MAP)) ÷ 255

Using a LO-MAP value of 10° and a HI-MAP value of 20°, with an octane number of 128 will yield a ignition timing value of 15, a 50% shift.

With the same map values, and an octane number of 250, ie 5 counts have been deducted, this yields an ignition timing value of 19.8°. Only a 2% shift, so the shift from the HI-MAP to the LO-MAP is gradual.

For the code bashers out there, if the starting octane number was lower, the shift to the LO-MAP would be faster. For example, if the start number was 50, and knock count had caused degradation to an octane number of 45, the result would be 19°, a 10% shift, not 2%.

If the knock sum is greater than 5 then the octane number will be decreased by 1 on a timer.
If the knock sum is 4 or 5 then the octane number is left alone.
If the knock sum is less than 4, then the octane number will be increased by 1 on a timer.

It has been reported that the octane number recovers to normal or near normal, quite quickly if the engine experiences some moderately high load with minimal knock counts eg 0-1. The ECU has to know it has been in an operating condition which would previously have produced knock. If it sees no knock, it will adjust the octane number back quickly.

This is good news, as it allows for rapid recovery by adding some better fuel or octane enhancer product if a dud batch of fuel has been supplied. The ECU holds the current octane number when the ignition is switched off. However tuners have reported that with some ECUs the octane number resets to 255 (100%) if the ECU is disconnected.

 

I don't understand this way of thinking, if it ain't knocking, why set them both the same. If it knocks high enough to cause a big octane dip during tuning, then get the foot out of it. The number recovers fast enough.