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Thread: Interesting Issue: MAF failure = Idle tables ignored. Cant tune VE because of it

  1. #1
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    Default Interesting Issue: MAF failure = Idle tables ignored. Cant tune VE because of it

    So im working on my 2007 Silverado with a 4.8 and ran into something interesting.

    I put a 224/230 .553/.546 111+2 Cam, bolt ons, stall, various stuff in the last week.


    What i found is when i cause the maf to fail by reversing the values in c0301 and c0302 (So i could dial in the V VE tables), the ecm completely ignored what seems like all the idle tables. It attempted to idle at 500 rpm with 28 degrees on timing. I did everything... changing the idle airflow, max idle area, and idle set points all over with no change in the way the engine tried to idle.

    After a lot of searching i found a obscure post about a similar issue stating on some e38's... the ecm ignores the idle tables when a map/maf failure is detected. So.....

    I put the maf settings back so it would not fail... and boom... it instantly idled and appears to respond to my changes in the idle tables.

    So if i cant fail the MAF.... how am I supposed to log and tune in SD to get my VE dialed in?

    I appreciate any help. TIA

  2. #2
    Joe (Moderator) joecar's Avatar
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    When the ECM ignores idle tables on MAF fail, which tables is it using...?

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    it is worth pushing your VVE table up and down. For example try 15% up and see if it gets better. SD MAF on scan should match Real MAF. Roughly that is. If your setup has moved the airflow away from stock too far, yes idling may be a challenge.

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    Quote Originally Posted by joecar View Post
    When the ECM ignores idle tables on MAF fail, which tables is it using...?
    It uses the high octane spark table rather than the idle spark. B1829, B1821, b1651, b1652, all what seems like all the idle tables are not referenced Whatsoever. You can change the values to whatever you want and log it.... it will act exactly the same. Tries to idle at 500 rpm using the high octane spark table. Its like the ecm loses its mind without the maf. Really frustrating.

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    Quote Originally Posted by gmh308 View Post
    it is worth pushing your VVE table up and down. For example try 15% up and see if it gets better. SD MAF on scan should match Real MAF. Roughly that is. If your setup has moved the airflow away from stock too far, yes idling may be a challenge.
    Have tried this with no luck unfortunately. Im nearly positive it is not referencing the idle tables.

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    Can you post your tune file?

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    Yes sir I can albeit a bit reluctant due to embarrassment lol

    I had a turbo car i built when i was 19 back in 07-08... Put a SD operating system on it and tuned the car easily. Car is still driving around 10+ years later with my tune. But this e38 has me really screwed up.

    Its currently set up totally open loop with DFCO turned off. I basically turned all that off... started with idle stuff till it idled well enough to drive (intending yo return to it and do it right). Then was going to put it into SD and tune the VE table. That is where i can into this issue. So i hacked up the maf table and a number of other htings till the truck ran ok and left it there lol. The Truck idles fair and driving it is surprisingly bearable with this hacked up tune. But id like to do it right!

    Be easy on me lol.


    5.29.19_R0005.ctz

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    Try this tune file, it's set for SD.... let me know if you still have the idle issue.
    Attached Files Attached Files

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    Quote Originally Posted by statesman View Post
    Try this tune file, it's set for SD.... let me know if you still have the idle issue.
    Thank you. I'm Nashville till Saturday so ill load er up on the truck when i get back! Illl report back then. Though your changes look pretty similar to that which i already tried.

    Would you like me to post a log of me trying it when i get back ?
    Last edited by Dragframe; June 27th, 2019 at 01:14 PM.

  10. #10
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    Quote Originally Posted by Dragframe View Post
    Would you like me to post a log of me trying it when i get back ?
    Log not needed... but if still has the idle issue, then give me a list of all the codes it's throwing (DTC's).

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