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

  1. #11
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    Quote Originally Posted by statesman View Post
    Log not needed... but if still has the idle issue, then give me a list of all the codes it's throwing (DTC's).
    So its a no go. Truck wont idle. Throws a p0103 code like one would expect. Same symptoms I describe above. Just doesn't even attempt to hold the set idle speeds. If i'm not holding the throttle open, it drops to 300-400 rpm.

    Loaded the other tune back in it, and idles great. Its like the ecm just freakin loses it without the maf.

    I've tried failing the maf in the tune... or removing the wire from the maf... tried removing the wire and making it fail quickly in the tune. All with the same result. Ecm doesnt even attempt to hold the idle speed.


    Now i have not in all this time attempted to drive it in Sd. i suppose even if a person couldn't make it idle in sd... he could still try to drive it around to tune the VE table? Im starting to believe i got a stange e38. Would straight maf only be a viable alternative?
    Last edited by Dragframe; June 30th, 2019 at 03:11 AM.

  2. #12
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    Quote Originally Posted by Dragframe View Post
    Would straight maf only be a viable alternative?
    Definitely.... that's how I run my own vehicle. Most people don't give the MAF sensor the love it deserves, but it really does work well when tuned correctly.

    I had hoped that if you still had the idle issue that your PCM would give us some codes to point us to the problem... it certainly is a weird problem that I've never seen before. I've got no idea why your PCM doesn't like going into SD, but if you're happy to run MAF only then it's something I would recommend.

  3. #13
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    Quote Originally Posted by statesman View Post
    Definitely.... that's how I run my own vehicle. Most people don't give the MAF sensor the love it deserves, but it really does work well when tuned correctly.

    I had hoped that if you still had the idle issue that your PCM would give us some codes to point us to the problem... it certainly is a weird problem that I've never seen before. I've got no idea why your PCM doesn't like going into SD, but if you're happy to run MAF only then it's something I would recommend.
    I enabled the maf from 500rpm up and the wideband seems to hold a more stable afr. Idle is a bit strange running maf only. Hard to describe. But it seems to drive well overall. Also seems to go into PE quicker for some reason. Might be something i play with going forward.

  4. #14
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    So what would cause low vacuum when on MAF only? Finding that with running maf only (no other changes), im dealing with vacuum/brake issues that i hadn't run into before. I have read a lot of guys have issues with "big" cams and maf only.

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    List everything you've changed/modified on your vehicle.

  6. #16
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    Quote Originally Posted by statesman View Post
    List everything you've changed/modified on your vehicle.
    its a 2007 4.8 with the Cam listed in OP... ls6 valve springs. 1 7/8 long tubes.. 3" Y pipe.. full 3" exhaust with open style muffler... 3200 stall converter... 4.56 gears.. and nitrous.

    I put on a cheap cold air intake on yesterday and it didn't seem to affect the tune (pretty much why i never bothered with a CAI lol)


    Also! Ever since i put the gears in the dash lights up like a christmas tree after 10 min of driving. Pretty annoying but have searched and haven't found a fix

  7. #17
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    Quote Originally Posted by Dragframe View Post
    its a 2007 4.8 with the Cam listed in OP... ls6 valve springs. 1 7/8 long tubes.. 3" Y pipe.. full 3" exhaust with open style muffler... 3200 stall converter... 4.56 gears.. and nitrous.

    I put on a cheap cold air intake on yesterday and it didn't seem to affect the tune (pretty much why i never bothered with a CAI lol)


    Also! Ever since i put the gears in the dash lights up like a christmas tree after 10 min of driving. Pretty annoying but have searched and haven't found a fix
    You need to change the gear ratio. I believe its called the final drive ratio on the ECM/TCM combo's

  8. #18
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    +1 on gear ratio. And also tire size.

  9. #19
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    Quote Originally Posted by joecar View Post
    +1 on gear ratio. And also tire size.
    I did hange the gear ratio in both the ecm/tcm. I didnt change the wheels/tires on the truck so i didnt mess with that. Though it does have some really freaking strange numbers in there for the tire size. But the speedo is dead on and it shifts fine and thats what it was when i got the truck and its was completely factory

  10. #20
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    Posting a response so the next guy with the same issue figures it out.

    b1703 is what table needed to be adjusted to allow it to idle without the maf. It had a really low number like 60 in the field. I just entered the values from b1701 into it and it idled I was able to get my VE table fairly close'ish. One thing to note though... the transmission must default to full line pressure without the maf because after setting everything up to tune the VE... the tranny was banging shifts and blew a cooler line. i didnt log any transmission parameters, i only took two drives to get my lower VE tables close ish, then turned the maf back on. Having a loaded dyno and being able to lock it in a gear would have been awesome to get all the VE dialed in. Maybe ill revisit the VE later

    I still have a crazy issue with turning on STFT. They jump all over the place with no rhyme or reason. Even at idle. I have them turned off for now. Maybe forever lol

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