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needed ecm do it need to be reprogramed to idle?

This is a discussion on needed ecm do it need to be reprogramed to idle? within the General Help forums, part of the LSx Technical Help Section category; I took my car to the dealer about the charging issue and I was told that I needed a new ...

  1. #1
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    pewter
    99 Trans Am

    needed ecm do it need to be reprogramed to idle?

    I took my car to the dealer about the charging issue and I was told that I needed a new ecm I hope that's what he called it. Do you have to reprogram it in order to make it idle. This is whats going on with my TA that had a charging issue. The car was running fine when I took it to them but now they say they are trying to get it to idle after they installed the new ECM. I hope that they did not run my car hard and have messed up something in my car. what do you guys think? and is this something that happens when you change ecms?

  2. #2
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    '02 WS.6 / '07 Suburban

    After disconnecting the battery (first step in swapping the PCM) the engine will run like crap on initial start up. It should clear out though very quickly and then idle fine. I am concerned that they may have misdiagnosed your actual issue and created a new issue. Was the SES light on when you took it in to them? If so, what were the codes?

    Idle issues can be the result of a dirty throttle body or MAF (especially with a K&N style air filter), a faulty Idle Air Control Valve (IAC), a cam or crank position sensor going bad, loss of fuel pressure, etc. If it starts and runs if you crack the throttle open, then start with the first three in this list. Also, make certain they installed the correct PCM for your car. Question: Has your PCM been recalibrated in the past due to modifications?

  3. #3
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    pewter
    99 Trans Am

    There was no lights and no modifications done to the car or the PCM. the car run great but it would only charge the battery if driven below 70mph. The tech said that there was no voltage found coming from the PCM which control the charging of the alternator. when I took my car to them the car was running great, that was Thursday went back to them Monday to get my car and take it somewhere else and it was running ruff and died when I put it in gear,Tech told me that the car was not charging at all now because of no voltage coming from the alternator, what do you think? I thought that once you installed the new PCM the car would not need any tuning after running for a while.
    Do the ws6 carry the same PCM as the stock TA.I ask this because I have a ws7 decal on the rear of my car and I hope this was not used to order the new PCM.I took my car to them because I got tired of trying to solve this issue without the needed equipment to fix the car. I hope I have not made a big mistake.I have owned the car 16 years only 45,000 miles on it and never been in a shop before because I did all of my own repairs.
    Last edited by Street Fighter; 05-21-2015 at 05:52 AM.

  4. #4
    Spaz is My Mentor SMWS6TA's Avatar
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    Navy Blue Metallic
    98 T/A w/a little mods...

    check the thin small wire coming off the Alternator to the wire loom. If this wire is broken or not attached to the alternator the pcm will not charge the battery. This wire has a common history of getting broke when changing because they either don't know it's there or forget to reconnect.


    Here's a thread that will show you what I'm talking about.



    A Fix if You Break your Alternator Wire Plu

  5. #5
    Spaz is My Mentor SMWS6TA's Avatar
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    98 T/A w/a little mods...

    Rereading the thread I hope you weren't taken for a ride. It is very rare that a ECM needs changing.



    1) There are different ecms depending on the yr of car. 98's have on, then the 99-00's, then the 01-02 yrs. All three are different but have the same default tune. The difference is the processors, for example .. 98's = 256kb, 99-02's = 512kb, 01-02 = 1MB.

    2) Limp mode - if the ecm detects a severe decrease of voltage in certain conditions it will go into a limp mode. It will surge the idle to about 3k rpms to force the alternator to charge the system. You'll know your in limp mode because it get's loud as hell and you'll feel like it's running away. It should only last about a min, but if the alternator isn't charging it will try to keep it going. Need to shut car off other wise engine damage could result. The ecm doesn't always go into limp mode, it has to have certain conditions to do so. Not sure what all they are, I just know when mine did it it scared the hell out of me that I thought the throttle body was stuck open.
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  6. #6
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    pewter
    99 Trans Am

    The tech at the dealership told me that my trouble started when I replaced my alternator and broke the red wire that connects to it.
    ,I put the wire back together my twisting them and taping them back together. I was told that doing this instead of soldering them together caused resistance in the wiring and caused the ECM to short out. he said that there was no voltage coming though the red wire to the alternator. which caused it not to charge. I got the car back today they install the ECM and soldered the wiring,wanted to install alternator but it was under warranty so I did it myself. car is charging now and not falling to discharge when I nail it. hand stays at 13.5 volts, I noticed that the car seems to be ldling a little low at times is this because of the new ECM like stated to me and that it is going to take sometime before it learns the correct idle speed.how much of this is fact and what part may be lies.Either way it's charging and paid for now so it's too late to worry about it.I had it running after installing it's battery that was charged up because it was way down. The engine was ldling fine and jumped to 2000 rpms and would not come down. what's up with that?
    Last edited by Street Fighter; 05-21-2015 at 05:03 PM.

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