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Discussion Starter #1 (Edited)
Is there a "textbook" way for a PCM re-learn?



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Discussion Starter #2
AND......

Do I take the silence as there is no one right way, or no one knows:-?
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I don't know and would like to find out, but I seem to recall that you can RESET the PCM by pulling some fuses or disconn. the battery for a while. Then there's idle relearn and some other stuff.....anybody?:-?
 
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I have written several posts on this and can be seen at

Proper relearn Process

Depending on if the power was removed from the PCM for a few minutes is different then if the power is off for hours also clearing out the NVRAM.

John
 

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Discussion Starter #6
So.....

Thanks John.

So if you install the intake of your choice, must you disconnect the battery and then do the re-learn, or will the PCM "see" the change and make the needed adjustments during the re-learn without d/c'ing the battery?
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Re: So.....

The only time you really need to blow the PCM's two memory areas ( RAM and NVRAM) is when you make major changes and want to start with a clean slate.
A minor change such as swapping aircleaner will get re-learned within a short timeframe.

A negative of dumping PCM memory is all the EPA I/M tests are also lost, forcing PCM to suck up some of its time redoing those tests until they are back in a completed (passed) state.

Short term fuel trims are relearned within 10 minutes and long terms within 1 hour engine run time.

Do not confuse a idle relearn process with a full PCM relearn or crank position relearn process.


fyrcaptain said:
Thanks John.

So if you install the intake of your choice, must you disconnect the battery and then do the re-learn, or will the PCM "see" the change and make the needed adjustments during the re-learn without d/c'ing the battery?
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frycaptain,

I installed the Halltech T-1 intake a couple weeks ago and the directions from Halltech were similiar to what teamzr1 posted below (this is with or after a disconnect of the battery.)

Keep in mind that there also is a re-learn process that needs to be done for correct idle.
In most cases you would for a MN6 based C5:


Cold start and idle for 5 minutes ( all power functions are off)

Turn on A/C only and continue to idle for aother 5 minutes

Turn A/C off, continue to idle for 5 minutes


I went out for a 50 mile drive after that to check things out and so far no codes.


PCM idle relearn thread
 

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Discussion Starter #9
Thanks guys

TeamZR1 and MiZ,

BIG thanks!:)
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About 5,000 miles ago, I installed a Borla XR1 Race Exhaust system. For the first couple of weeks, it ran great. Then it gradually got louder with more resonance, to the point where the sound drove me out of the car. I got so disgusted, I yanked it off and put the stock unit back on, except by then, I had installed headers and removed the pre-cats. It seemed to run fine, but I felt I was losing performance over a competition exhaust system and I didn't care for the sound. About 3 weeks ago, I installed the Corsa TI (titanium) unit, which is also a competition system. It immediately woke up the car, the sound was awesome and I thought I was finally done with mods. After about two weeks, the exhaust got louder, the resonance started creeping back in, and it started to vibrate and sound tinny. Am I a victim of Computer Re-learn? If I understand the process, now that I have opened up the car with an intake, ported throttle body, headers and the Corsa, the PCM thinks I have too much air and compensates by running richer. In a recent dyno run my air/fuel ratio was 15.0 at 3600 RPM but it dropped to 12.6 - 13.1 from 4500 - 6500 RPM. However, that was when I thought the car was running well. Do you think I am running too rich? Any ideas? What about the MAFT and Ease Scanners solutions I have been reading about? Any feedback you can provide would certainly be appreciated. :-?
 

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I think this happens to anyone that modifies anything on the Z, although not to the extent you have noticed. MAF translater is the best solution I have heard about.
 

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Hmmm...I would say that you have reached the gray area of the modification spectrum...where comfort is compromised in the name of performance. The performance level you can achieve is directly related to your threshold for NVH...noise, vibration, and harshness.
 

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Normally I might agree with you, however, when my Corsa system was originally installed, it sounded great. The car has adjusted due to the absence of back pressure (my theory) and I'm trying to determine what to do. As I wrote in my post above, the same thing happened with the Borla system I originally put on the car. There was no vibration, no harshness, only a good, clean (loud) exhaust note. I'm dealing with a moving target and trying to find the best way to hit it - MAFT, programming, fuel injectors, etc.
:-?
 

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Sounds like to me the packing in the mufflers has burned down some and therefore caused the exhaust system to be a lil louder.

The cat back system I have on my 01 Yukon XL has gotten a lil louder since it was brand new.
 

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As an update to what I posted last week, sometimes my exhaust system sounds perfect. Other days, it is incredibly obnoxious with an irritating rattle/vibration around 2700 rpm. On those days, the exhaust note overall is much louder. It seems to vary with the weather, probably the humidity. After New Years, I'm taking it to my GM Corvette Specialist to look at some timing or air/fuel adjustments. I'll let you know if any thing turns up.
 
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