Part 1

In the EVO ECU, there are two fuel tables and two ignition timing tables. The fuel tables are laid out in a 15x18 cell arrangement and the ignition tables are 20x19. One pair is for high knock conditions and the other pair is for low knock conditions. The high knock tables are richer and less advanced. Conversely, the low knock tables are leaner with more ignition advance. The "space" between these fuel and spark advance values is where the engine operates at 99% of the time. When it comes to reflashes the factory code, the tuner can make this in-between "space" narrow or wide as the Grand Canyon-- either approach offering different pros and cons. It's basically a trade-off between consistency, adaptability and margin of safety against knock. The best compromise will depend upon under what conditions the car is subject to (drag race, road race, dyno bragging, etc,.)

First let's look at the ignition table(s). There are 19 load points and 20 RPM points. The RPM points are spread out in 400RPM increments from 400RPM to 8000rpm. The load points are spread out in calculated boost increments from heavy vacuum to approx 22psi. (Since the EVO does not have a MAP sensor of sufficient range, boost is calculated internally by comparing MAF with RPM). With a resolution of 20x19, there are 380 cells in the ignition tables to play around with.

The 15x18 fuel table(s) follow similar suit with just 270 cells to play with. Each RPM point is separated by 533rpm (8000/15). And the 18 load points covers the area from heavy vacuum to approx 22psi.

more to come....

 

Good info for everyone to be aware of.. This isn't common knowledge for alot of people.

 

Shiv, to your knowledge are there gear-specific maps in the stock ECU? If so what role do they play?

 

I just want to say how much I appreciate being told this kind of information. It seems that this kind of informaiton isn't much of a secret when it comes to tuning shops, but for some reason none of them want to tell us(the consumer). I hate not knowing what kind of changes are being made in my ECU(flash) or how a piggyback will interact with the ECU. Makes me want an Xede that much more. [yells through the house]honey... I need to spend a grand on my car[/yelling]

Mad props Shiv.

 

So, the ECU can't, for example, see more than 22psi unless the MAP sensor is changed?

 

So, although there are only two maps for fuel and two maps for spark, the ECU isn't limited to one or the other (like a light switch)? They can progressively shift in either direction (like a dimmer knob)?

If I'm right, how does that differ from the AEM knock feature?

 

I don't think the MAP sensor can sence much boost. I'm not sure what the limit is, but its way under 22psi. I'm not sure why.

Load or Boost is calculated by esentially dividing the Mass Air Flow(MAF) by the RPM and multiplying by an offset. This gives Lb of air per engine revolution. Right?

 

The AEM allows you to set knock thresholds based on engine RPM and adjust fuel and timing if knock is detected (based on settings).

If your threshold is reached, then you can add a specific amount of fuel per volt and retard timing the same. You can also set values for how much to correct once knock is eliminated.

The stock ECU is way more advanced when it comes to knock detection

Mark

 

There are no gear specific maps. It isn't really required.

 

More please



Bump

 

I'm working on it

As for gear-specific maps, yes they are there. Well, actually they are road speed specific maps. But road speed and RPM are used to determine gearing

shiv

 

Shiv, no kidding? Is it just an addition/subtraction factor based on road speed?

What you mention about the two maps is also in the DSM ECU. One map is the high octane map, and the other is the low octane map. When the ECU wants to look up timing for a particular load and RPM, it reads the value out of both maps, and then uses an octane number, or long-term knock number to pick a value between those two map numbers. On a DSM, long term knock is usually zero, so the high octane map is used. The low octane map should only ever be used when someone pumps gas into the car that does not meet the factory's minimum octane requirements. The long term knock value (which Todd Day called octane) really shouldn't budge in a perfectly working DSM.

How does the Evo ECU choose a number between these two tables?

 

That isn't too much of a suprise, but it's nice to know. As drag increases and the engine needs to work harder in a give RPM range, the tuning requirments would change.

Thanks for all the great info!

 

Shiv, by any chance that you can post up the two EVO's factory fuel and Ignition maps (absolue value). I just want to see it as a reference to start tuning. It will also be very interesting for us to see how much difference between the two map. Thanks!

 

It's been almost a month... please feed my brain... it NEEDS Part 2!!!