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Discussion Starter · #1 · (Edited)
Hello all, I replaced my battery today and while driving noticed the car seemed a little "sluggish". I had my ECM tuned a few years ago by PCM4less and currently have modified the exhaust (header and cat). I have read that disconnecting the negative terminus from the battery for a period of ~30 minutes will clear the ecm. Is it reasonable to presume this has occurred with my ecm? That is, the disconnect has cleared/deleted the tune and is presently "re-learning"? As always, any and all input to the matter is welcomed and appreciated.
 

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Nobody's helpin' a brother out here?

It is my understanding that the disconnect of the battery should not clear the tune. Those are variables that are stored in data tables of the code in the ECM. They have to be "flashed" into memory.

Soup may be able to shed more light on it, like whether it is stored in NVRAM, etc.

Anybody else that has a tune that can give more specifics? (I'm just going by what I've read.)
 

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You are correct chickenwire.....mine is tuned and I've disconnected the battery and also replaced a battery. Neither removed my tune.
 

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I have a general motors tune and the Trifecta tune installed. I have disconnected my battery several times; i.e. water pump change, battery change, and disconnecting the positive terminal to clean corrosion. Both of the tunes have not reverted back to the stock tune.
 

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The only thing that I can think of is that the ECM has to go through a relearn ? process if the battery has been disconnected or the car sits for a long time. I have had an issue with my car getting an E Check because of this. The procedure to clear this is to start the car and run it for around 10 miles to get it up to operating temperature then shut it off and repeat 7 to 10 times per my GM dealer this resets the ECM something to try .
 

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Your tune should never leave your ECM. It’s written in ROM, not RAM. ROM , for those that know nothing about computers, is Read Only Memory….it cannot be changed, even when power is disconnecte, unless overwritten by something else. ROM is like a hard-drive on your computer. RAM is Random Access Memory that is ‘volatile’. What that means is when power is disconnected from RAM, it loses all information. RAM is used for changing parameters of the engine on the fly, so for instance your AFR. RAM is faster then ROM. Therefore most of engine parameters are run by RAM, but those parameters are pushed on initial power-up by ROM. Make sense?

With that said, your tune SHOULD NEVER delete itself, unless your tuner has put a bug in the code to delete it by certain actions....
 

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That's bizarre. I was just about to start a similar thread.

I replaced my battery on Sunday, and when I took it for a drive I had absolutely NO BOOST. Nothing. Nudda. Zip!!

Thinking that I had lost my tune, I pulled out my laptop and re-flashed her. Went for a drive and back to crazy power. Then yesterday I was driving around doing errands and after 4 or 5 stops and starts of the engine, I once again had no boost! No codes or anything. No boost and incredibly sluggish. Felt as though I maybe had 80 HP.

I pulled over to the side of the road and let her sit for a minutes or so, re-started her and she is now back to normal.

What is going on.
 

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Discussion Starter · #8 ·
Thanks for the responses everyone. In the event that it needed to go through re-learn cycles I have been driving more aggressively (when safe enough to do so) and am able to fortunately inform you that the car is back up to or nearing previous performance levels.
 

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As Ghost mentioned there are parameters that get recalibrated on the fly.
You may also check your battery connections since the last thing you did was change the battery.
There are also cycles that the ECM needs to go through on certain parameters.
Not sure if this applies to your tune from PAW, but is a good place to ask.
 

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Ok let me wade into this moras . .. . LOL

The memory in the ECM is a combination of several types. There is "burned in" fixed memory on PROMS. Programmable Read Only Memory. This is generally true of every computer. The ECM is basically a dedicated single board computer that is used in multiple different applications within the range of GM products. The PROMS are like the BIOS, when the system boots up the data that tells the multi purpose hardware what instance it is usually is contained on the PROMs on the motherboard.

There is probably some type of non-persistent memory but the majority of the memory is persistent. Persistent means it retains its data when power is removed. But it is read / write memory accessable by both the ECM operating system and can be programmed externally.

The ECM operates on a set of rules and algorythms. These rules and algorythms are persistent and generally can't be changed without pulling the SBC and operating on the fixed memory PROMs. For example, if it is built as a C6 corvette, it takes reprogramming of the persistent and probably the PROMS to turn it into a Solstice 2.0 ECM.

The non persistenct memory contains data only as long as power is applied. When you shut down the computer and turn it OFF, the non persistent memory will loose its charge and its state. Ones and Zeros become no state probably zeros. non-persistent memory is used as input output or scratch pad short term memory. A register that contains the current input from the MAF for example. It is needed "on the fly" by the OS to receive or send data but not kept long term. It is generally cheaper and faster.

Persistent memory is used to hold the "tune" data. As stated above, the tune is a set of rules and algorythms. They do nothing by themselves, but they operate on input information (data) and use that input information to figure out how to operate on information (data tables) that are used by the rules and algorythms to command the various bits and pieces of the engine.

Stated another way, the temperature sensor sends a data word to input memory. The operating system "pulls" that data word, inputs it into the appropriate algorythms which then point the operating system at specific cells in the "tune data tables". The tune data tables hold the verious values that drive the commends to the engine through the algorythms and rules. For example, if the temperature is read as "high" then the value drives the operating system through the proper algorythms to specific cells in the data base which might be timing information. When, how long etc.

The "tune" then consists of the rules and the data tables.

The rules are generally "permanent" on PROMs and never go away. Some can be reburned but that is a different subject. Think of the rules and algorythms as fixed imutable and permanent.

The "tune" that is added either as the GMPP tune or an alternative tune generally changes the data contained in the tables. The algorythms and rules do not generally need to change to realize performance changes, and frequently are not accessible without the proper hardware tools and knowledge.

All the above suggests that
The basic program is persistent and will not change with change in state of power

the data tables used to control the engine paramaters is persistent and is not affected by change in state of power

the non persistent data is zeroed out every time that the power is cycled as it is throw away data used only for real time control

There is a special case of data which is non-persistent but which is "kept alive" when the car is powered "off". This data, codes, state information needed for the next start cycle etc are retained in non-persistent memory. This means that the ECM / BCM keeps power applied to this special memory even when the car is in an off state. And this memory is cleared when you force the ECM / BCM into a zero power state. By removing the battery cable for ~30 seconds you can clear this state memory of codes and trim data that was saved from the last run session. The ECM / BCM is designed to work this way.

My experience is that if I want to clear a code, I pull the battery cable for a count of 30, then reattach the cable and the car will start and run normally but the codes are cleared.

If I pull the battery cable for 30 minutes, then most or all of the non-persistent data is cleared. This the equivalent of factory reset.

So, short power removal clears codes and some memory state data. Long power removal clears most / all of the non-persistent data and returns the ECM / BCM to its "factory baseline" state.

If you clear codes, 30 second power off, my experience has been that the learned tune / trim data is retained so the car does not have to "re learn" to a higher performance level.

If you clear memory, ~30 minute power off, then the ECM / BCM clears all non-persistent memory and returns to its factory tune settings and will need to "learn up" to the maximum potential over the course of several key cycles.

I do not have actual engineering data that supports this understanding but I ahve worked on a lot of computers and this is what I have observed. If anyone has better information or has a different interpretation then I am happy to see it.

:grouphug:
 

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Rob, is there a webpage that one can understand and learn on how the onboard engine electronics for the GXP or the NA are computed for attaining the performance targets in the data table, or is this proprietary info only?
 

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ROM = read only memory. It's burnt into the chip and cannot be rewritten. The chip would have to be replaced.

PROM = programmable read only memory. Can be altered in the chip with the correct device.

NVRAM = Non-volatile random access memory. Can accept new data and retains it until it's desirable to modify it. So it shouldn't change when the power is disconnected. Example would be station presents on an electronic radio.

So a combination of all the above could be at play, but everyone's contribution, collectively, is correct. (We tend to do that alot, don't we?) lol

Yell - as for the data tables being "proprietary" I'd say, yes, kinda. Many who got into the tuner market are former car company employees that learned that kinda stuff. As it is their business, I'm sure they're not going to just go out and publish a "how to".

However, given a good search engine and some persistence I wouldn't be surprised if you could learn a few things out there on the interweb...
 

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Alright Chicken, when I went to school it was all called ROM! LOL... Rob, as far as clearing your codes after 30 seconds....kind of. While a code reader won't see the code and you CEL will be off, the code is still stored in memory and can be pulled at anytime. I, for instance, have had an O2 sensor code set 8 different times. Also, my computer has been re-written 6 different times. How do I know this? A friend of mine is an engineer that works for GM and he pulled all of this out of my computer. So all of you with a Trifecta tune that you turn on and off....are in fact, re-writting you ECM. Therefore many of you that turn it on and off have accumulated times that you've re-written your ECM..... a safety feature that GM put in the ECM so that they can tell if you tuned your car or not if you had a major failure but had a factory tune in your car when it came to the shop. In other words let's say you had a Trifecta tune with a 7000rpm rev limit....you throw a rod racing one night and immediately "turn off" your tune. Let's say that you've had the tune in your car for over a year and you turn it on and off from time to time. An engineer is called out to look at your engine to "figure out why you threw a rod". Upon inspection he figures out that it was because of excessive rpms. He then hooks up a computer to your ECM and finds out you have rewritten your ECM over 200 times.... chances are, your warranty won't cover the damage....
 

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I bought my GMR TUNE ecm off of another forum member, installed it in my sol, had to do the crank position relearn and that was it, It runs better.

1 thing is that I didn't know what performance parts the previous owner had...... so I dont really know if my car is getting any real performance? Is there Anyway of knowing this?
 

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You left out EPROM's :). anyway, that's enough knowledge for one day, think I'll go back to bed now.
 

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Just one more, there are also EEPROMS...:D

EEPROM (electrically erasable programmable read-only memory) is user-modifiable read-only memory (ROM) that can be erased and reprogrammed (written to) repeatedly through the application of higher than normal electrical voltage. Unlike EPROM chips, EEPROMs do not need to be removed from the computer to be modified.
 

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Alright Chicken, when I went to school it was all called ROM! LOL... Rob, as far as clearing your codes after 30 seconds....kind of. While a code reader won't see the code and you CEL will be off, the code is still stored in memory and can be pulled at anytime. I, for instance, have had an O2 sensor code set 8 different times. Also, my computer has been re-written 6 different times. How do I know this? A friend of mine is an engineer that works for GM and he pulled all of this out of my computer. So all of you with a Trifecta tune that you turn on and off....are in fact, re-writting you ECM. Therefore many of you that turn it on and off have accumulated times that you've re-written your ECM..... a safety feature that GM put in the ECM so that they can tell if you tuned your car or not if you had a major failure but had a factory tune in your car when it came to the shop. In other words let's say you had a Trifecta tune with a 7000rpm rev limit....you throw a rod racing one night and immediately "turn off" your tune. Let's say that you've had the tune in your car for over a year and you turn it on and off from time to time. An engineer is called out to look at your engine to "figure out why you threw a rod". Upon inspection he figures out that it was because of excessive rpms. He then hooks up a computer to your ECM and finds out you have rewritten your ECM over 200 times.... chances are, your warranty won't cover the damage....
Agreed. Good points.

Early on when we were discussing the upcoming GMPP tune, there were questions about the ECM software. A GM engineer indicated that there is a record kept of each time the ECM software is modified as you referenced above. At that time they said that it could not be acessed unless you pulled the computer and hooked it up on a bench with the proper GM tools. I was not aware that each time you turn on an after market tune it was counted but it does make sense.

:thumbs:
 
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