Airflow and PCM memory.........GMPX, Blacky, gojo, Delco...

[bink]

I have 2 questions:

1.) When we do an Idle Relearn (Y-Body) what value is retained in memory and what type of memory is it?? Is it the long term idle value-> IAC_LTD_DMA ?? This value is erased when we flash the PCM.

2.)What Airflow value is retained after a PCM flash and is erased by battery disconnect ( of more than 2-3 minutes)?


Cheers,
joel

[Delco]

I have 2 questions:

1.) When we do an Idle Relearn (Y-Body) what value is retained in memory and what type of memory is it?? Is it the long term idle value-> IAC_LTD_DMA ?? This value is erased when we flash the PCM.

2.)What Airflow value is retained after a PCM flash and is erased by battery disconnect ( of more than 2-3 minutes)?


Cheers,
joel
A reflash or a battery disconenct erases all the learnt trims , idle,fuel and gearbox.

[jfpilla]

I have 2 questions:

1.) When we do an Idle Relearn (Y-Body) what value is retained in memory and what type of memory is it?? Is it the long term idle value-> IAC_LTD_DMA ?? This value is erased when we flash the PCM.

2.)What Airflow value is retained after a PCM flash and is erased by battery disconnect ( of more than 2-3 minutes)?


Cheers,
joel

Joel,
I'm not sure about the question but if I understand it, as Delco says, all trims are removed with flash or a battery disconnect. Table values are not removed, only the trims, that's why a really good tune doesn't need a lot of relearn. That's a dream though. The LTFT's are constantly trying to force the STFT's to 0. External conditions keep the trims working hard.
Idle relearn, I think, is only a method for getting the idle acceptable, quickly, by keeping the idle cells active exclusively. Hope I didn't miss you're point.
Joe

[bink]

Thanks for the replies! :D

I should be more specific. I'm open loop- so fuel trims aren't involved.
ETC here (C5) - of course you know this Joe :lol:.

If I flash the PCM my Long and Short Airflow trims reset . But there is a learned value(s) held within the PCM that is/are only erased with removal of power (battery disconnect). Seems like this would be the same type of memory as the clock??

If I flash a new tune the idle will improve more quickly IF I don't pull the PCM fuses. If I pull the PCM fuses it takes longer to learn and improve.


If I scan cold startup DESIAC AFTER, a flash and pulling the fuses and then do a second flash and scan, on a different day and don't pull the fuses, the second day DESIAC values will be about 2 g/sec less than the 1st.

If I flash Tune A. drive the car for 45 minutes and then reflash with Tune A (always doing an Idle relearn) it will transition to idle from a rolling stop (throttle cracker) very well.

If I Flash Tune A drive 45 minutes Reflash AND pull the PCM fuses (and do an Idle relearn) it will stumble or fall on it's face as it transitions to idle from a rolling stop. Also the Throttle Cracker and Throttle Follower Airflow will be inadequate between shifts. If I drive it for about 40 minutes it will learn itself "in" but I have nothing I scan that would indicate this.

I think there must be a compensatory value(s) held in the PCM.
I was hoping you guys would say " Sure, It's xxxx". :mrgreen:

This isn't a big deal...it's just something I've seen since way back when NoGo and gameover were hashing out the VE equation. My AFRs were leaner if I didn't pull the fuses with each reflash. I'm just curious about the cause/effect.

Have a great and safe weekend!!

Cheers,
joel

[Ira]

Flash memory can't be erased by removing power. Because so many things change when power is removed there must be a section of battery backed RAM in the PCM that's used to store persistant information. It might be something in that area that's causing your issues. You'd have to ask Paul or GMPX if they touch that area during a flash and if so, what they do to it?

Ira

[jfpilla]

Joel,
I didn't think we answered the first question. It was too easy. However, this question is hard, since I and others I know experience similar inconsistancies. Some of it has to be a result of changing conditions, but not all of it. It does seem like there is some information saved under certain conditions. So, like you, it would be interesting to me to get an answer, but not too important since it all clears up quickly with little impact. I do sense that a well done tune goes to running well right away. By the time weather affects that tune, with an MAF, the trims are helping.
Joe

[bink]

Joel,
I didn't think we answered the first question. It was too easy. However, this question is hard, since I and others I know experience similar inconsistancies. Some of it has to be a result of changing conditions, but not all of it. It does seem like there is some information saved under certain conditions. So, like you, it would be interesting to me to get an answer, but not too important since it all clears up quickly with little impact. I do sense that a well done tune goes to running well right away. By the time weather affects that tune, with an MAF, the trims are helping.
Joe

Joe - Thanks! :D It is a small issue ....but it bugs me since we can't "see" it.
Oh well. :lol:

Cheers,
joel

[GMPX]

Pulling the battery or reflashing looses everything 'learnt'.
We clear the NVRAM in the PCM on purpose, I am told that not all programmers do this :roll:
After every flash it will re-initialise it's RAM as though the battery was pulled.

Cheers,
Ross

Edited due to jetlag brain fade, I meant RAM, not NVRAM.

[jfpilla]

Ross,
That's good to know. Glad it all clears.
Thanks,
Joe

[bink]

Pulling the battery or reflashing looses everything 'learnt'.
We clear the NVRAM in the PCM on purpose, I am told that not all programmers do this :roll:
After every flash it will re-initialise it's RAM as though the battery was pulled.

Cheers,
Ross

Edited due to jetlag brain fade, I meant RAM, not NVRAM.

Thanks Ross and Joe.
Could it be a value learnt at startup - after a flash?
At start up- as the start up and friction air decay out???

Cheers,
joel

[GMPX]

The PCM does put some 'default' values in various RAM locations if they have not been learnt, look at the A/C offsets for example.

Cheers,
Ross

[bink]

The PCM does put some 'default' values in various RAM locations if they have not been learnt, look at the A/C offsets for example.

Cheers,
Ross

Thanks Ross.:D
This makes some sense. Could pulling the power ( for longer than 3-4 minutes) interrupt the default values??

Cheers,
joel