A Question to the ECU Guys

[shebangs]

This question is directly to the ECU guys on the forum, we know who you are, but I prefer not to mention names incase I forget anyone.

This is something that has had my curiousity for a while now. I'm a software engineering, but I have no experience in ECU programming. I do know how engines work.

I don't understand why people insist on resetting there ECU after any/some mods? They claim it's to reset the A:F ratio's (fair enough) - but based on my experience, why wouldn't the car always just use variables to control these values? Granted it would probably want backup values for any extreme sensor readings but other than that, I can't see it wouldn't.

So..not having seen the code and algorithms Honda (or any car) ECU uses, what's the answer? Are most people talking crap and the ECU always does use variables to control it's timings based on realtime sensor relay, OR does it use semi-static values? If it uses semi-static values, why?

Cheers,
Matt

[Weq]

ecu's in general are getting alot more advanaced. There is no one answer to this question, you have to be specific to a generation of car.

I know i will probably be corrected, but my abstract understanding of 0db1&2 honda ecu's is that they have basemaps, then they use the o2 sensor and maybe a few sensors to refine these maps. Specifically they have varaible correction tables (variables) stored in a RAM type memory configuration. By resettings, these correction values are lost. An ECU will adjust to any mod in due time, but some people (ie n00bs) think resetting the ECU will quicken the process. Theory dictates otherwise though, unless of course the mod's make 'corrections' more like the basemap, then without.

An example of where resetting an ECU will actually give noticely u less performance was with my old liberty B4. It had variables which indicated the car's health on a scale from 1-15. 15 being optimal and hence a more agressive fuel and igintion mapping. Therefor if you currently were running a value of 13, apon resetting the ECU, the default value of 8 was restored, giving the car less performance.

[ProECU]

The Honda ECU's, specifically OBD0 & OBD1 and i would assume the later OBD2 & K variants in particular (however I cant confirm this for the K's as I have not seen the code...YET) use trends in O2 voltages over time to make adjustments to fuel trim.

There is a Short term & Long term parameter which the ECU stores in RAM
essentially, the short term is used as a reactive response to the current O2 voltage and its relation to rich lean.

The Long term trim essentially is a trend over time, again for O2 voltage which is used by the ECU to determine the overall bias of the car towards rich or lean.

By resetting the ECU, you erase these parameters, and the ECU reverts back to sock parameters for these trends.
The short term is arguably irrelevant to long term performance, and is re-learned instantly.
The long term trim is erased and the car will need to re-learn this bias.

Does it give a performance gain.... I say no it doesn't, but I guess its arguable.

Following from this, the later K ecu's have a wideband O2 sensor, so one would assume the trends are much more specific and accurate.

Hope this helps.

[shebangs]

So it keeps a short term and long term trend analysis? But whats the definition of long term? Surely from my experience anything beyond a few minutes would be useless information? To me (and maybe this is what is done is new ECU's, even if in other manufacturers) it would be alot more beneficial to have the sensor feedback determine the realtime information, and any exceptional information be controlled by static mapping tables?

[saxman]

it's also important to realize that the ecu operates in open and closed loop. closed loop being where o2 readings and such effect driving. When you're giving the car a good amount of throttle to where performance would be noticable, the car doesn't care what the o2 sensor is telling it anyway, so resetting the ecu will not make any performance difference.

[bennjamin]

dosent resetting the ECU simply bring it to "adjust" to "relative" mods alittle quicker than say waiting a few k's worth of driving ?

[saxman]

dosent resetting the ECU simply bring it to "adjust" to "relative" mods alittle quicker than say waiting a few k's worth of driving ?
it basically resets the saved info from the o2 sensor, so it's starting the readings over from scratch. But it only effects low load, part throttle driving. Won't make a bit of difference when you give the car any gas.

[Weq]

dosent resetting the ECU simply bring it to "adjust" to "relative" mods alittle quicker than say waiting a few k's worth of driving ?

I called it a myth for a reason, and the above should explain why :)

[EG5[KRT]]

where i work we need to initialise any new parameters that are involved when doing work to a car i.e. change of voltage.. less resistance ..

so if any airbag(example) work is done it all needs to have all the faults cleared and re initialised to factory settings.

so wat ur saying is like that when u reset teh ecu it reinitialises the base factory settings b4 so pretty much off the shelf spec.. then once u drive the car hard the ecu will learn these new parameters ?

i thought only "reflashes" of teh ecu could really change the specs....

[saxman]

the ecu has the base fuel maps that everything is based off of, and then can make adjustements to that according to o2 readings, etc. It isn't rewriting the fuel maps or anything, just a small modifier to make minor adjustments for how the car is driving in part throttle/low load situations. I recall reading somewhere that the o2 sensor readings can only make about a +/- 5% change in fuel output, so it's not a huge change or anything.

[ProECU]

If you are really interested in how the Honda ECU's operate, get yourself a Decompiler and a .bin file, and start decyphering code.

It's the ONLY way anyone can confirm what I have said in this thread.