ECU learns

[gomez]

http://www.350z-tech.com/forums/index.php?showtopic=25195

thought id share something i just read..its about how the stock ECU learns our driving habit..i think..

 

[Applejuice]

dam it. got to log in to read. i dont have an account. mind sharing what its about?

 

[gomez]

oh sorrry bro didnt realise that.. ive attached a screenshot of the webpage

 

[gomez]

damn screenshot not clear =_=" sry2 ill fix it up soon

---------- Post added at 05:33 PM ---------- 6 hour anti-bump limit - Previous post was at 01:48 PM ----------

here are the posted stuff on the page:

I've read on quite a few posts where people say that the CPU will change to different performance settings based on your driving habits. This is puzzling. Is this true and what would be the reasoning for this - optimal gas mileage, minimal engine wear? I can comprehend that it will dynamically change certain parameters during normal driving based on feedback loops (e.g. fuel/air mixture).

Can anyone explain this in more detail? I had always thought that your CPU (ECU) was flashed once with a fixed range of settings. So I infer that there must be some type of dynamic memory in the CPU. Again I would've thought that it always would reset to a nominal set value each time you started the car.

So is there a way to keep it in its highest performance settings without always having to drive like a maniac? Would shifting at a higher RPM do the trick to keep it in the high performance mode? Excuse my ignorance but I'm very interested to learn more.

Thanks

The ECU assigns an "offset" or "long term trim" to correct for continual deviations from the fixed values that are stored in the ECU's lookup table. These deviations are caused by engine variances, weather conditions, grades of fuel and driving habits.

The idea of a "high performance" mode is more of a myth than reality. If you drive fast a lot, and an offset is required for high RPM operation, then this information is stored as part of the long term trim. If you don't drive fast, then the ECU will assume that the factory defaults are good when you hit high RPM. If they are wrong, then basic closed-loop operation will correct this.

When people give the advice of resetting the ECU after a mod, all they are accomplishing is clearing out the long term trim. Which the ECU will then get back to work rebuilding. You're just speeding up a process that will occur on it's own.

I can clarify a specific point more, if need be. But that is the basic gist of things.

Regards,
Ronin Z

No, that's perfect Ronin and thorough as usual. Thanks for the explanation. That makes total sense.

My only follow-up question is whether there is some type of defined 'averaging' cycle that the 'long term trim' uses. In other words, are these driving-habit induced values fixed in the ECU once they're set? If I drive moderately for 3 months (i.e. gentle highway cruising), will the long term trim then change back closer to the factory default settings versus having a higher 'offset' value due to previous point in time that I was driving fast a lot? If so, is it like applying a rolling average?

So in conclusion, I'm formulating an understanding that those folks, who in response to complaints about atypical sluggish response, are partially correct when they recommend that you go push your car harder in order to reset these offsets. Is that correct?

Basically the ECU is recieving either a RICH or a LEAN signal from the O2 sensors. When it receives the signal it will adjust trim in the opposite direction until the opposite reading is achieved, then reverse course. So if we get a RICH, it will lean up the mix until it gets a LEAN. If everything is perfect we will see a constant alternation between RICH and LEAN. When it starts to get a bunch of RICHes (or LEANs) in a row that's when it uses short term trim offsets to correct the situation. If these short term trims are required for an extended period, they become part of the long term trim.

OK, with that said. Once the engine finally warms up, it will swicth to the default factory base map, and will stay there if it can meet its target AFR using that map. If not, it will then default to the long term trim map, and use short term trim to adjust accordingly. So if driving conditions change dramatically the long term trim can be rebuilt in the space of a few miles of driving.

1. Prolonged low RPM use will result in excessive deposit build up in the combustion chamber. Routine romps on the throttle help clear and prevent these types of buildups. 2. If you never see high RPM the ECU can't build an offset for those RPMs. So it comes down to, would you rather have an offset that is at least close (that was pre-built from previous jaunts) or do you want the ECU to have to build one on the spot... right when that punk kid in the Eclipse rolls up next to you?

Regards,
Ronin Z

 

[Applejuice]

this is good info, thanks.

 

[gomez]

no problem, bro. just passing around stuff i read from other forums.

 

[TamanLinkin]

1. Prolonged low RPM use will result in excessive deposit build up in the combustion chamber. Routine romps on the throttle help clear and prevent these types of buildups.

so, guys...