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Thread: Openloop commanded afr issue

  1. #1
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    Openloop commanded afr issue

    Finished my heads and cam swap about a week ago. I drove the car over to a friends house and all the afr's were looking good. I just did some minor tweaks to the ve table on the way and everything looked good. It was ideling for awile when all of a sudden the afr's started going lean. I tried adding more and more fuel and it was like it wasn't doing anything to the afr. I limped it home and started checking everything!

    Here it is a week later and I have literally gone through it top to bottom. The car runs fine, idles fine, everything is good other then the fact that if I take it out of closed loop the thing just leans out and no matter how much I add to the ve table, it just wont correct it!
    Even in closed loop, the fuel trims are all over the place (lean).
    I have tried going into maf only mode and tried correcting the fuel that way to no success.

    Im at a loss if solutions at this point and the only other thing I can think of is something in the ecu just let go if that's even possible for one to do this.
    I have searched and searched for vacuum leaks ect. And no dice.

    Is there possibly a ground or something in the ecu that would cause this?
    any help is greatly appreciated! Has anyone else had a issue like this or am I in a boat by myself here?
    I have even tried putting the stock tune inand put it in open loop and same scenario.

  2. #2
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    Forgot to mention that I have checked fuel pressure also and its rock solid at 58

  3. #3
    Advanced Tuner vette_c6's Avatar
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  5. #5
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    that was a log of just driving around the block. Dont really want to go much further with afr's in the 16-17's.

  6. #6
    Senior Tuner mowton's Avatar
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    Did you clear the trims via the VCM control? Or as you said, maybe you have a thermal issue with an injector or a bad ground connection that opens up when hot. Log the injector duty cycle of the injectors to see if the PCM is trying to drive them full on to get you back to stoich.

    Ed M
    Last edited by mowton; 03-17-2012 at 05:12 PM.
    2004 Vette Coupe, LS2, MN6, Vararam, ARH/CATs, Ti's, 4:10, Trickflow 215, 30# SVO, Vette Doctors Cam, Fast 90/90, DD McLeod, DTE Brace, Hurst shifter, Bilsteins etc. 480/430

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  7. #7
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    I did clear the trims. I will log the duty cycle in closed loop and check on that. It cant be the injectors, I have a brand new set of fast 36lb. that i threw in it just to verify that it was doing it on both sets. I of course re-adjusted all of the injector data for them.
    Im in the process of pulling the intake back off to check all of the grounds on the back of the head.
    If that dosnt work I'm going to try putting the ecu from my trans am in it to see if its just a fluke ecu problem.
    Any other ideas would be greatly appreciated!
    Im running out of ideas.. lol

  8. #8
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    Another thing I just thought of... The cam being a tooth off or the cam just being ground wrong wouldnt cause this would it?

  9. #9
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    What happens if you put it in closed loop do the fuel trims go positive and bring it back to stoich?
    1997 Trans Am WS6 - LS1 swap - TR224 - Pacesetter Longtubes - Yank SS3600
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  10. #10
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    Sure does. Im heavily leaning towards either something in the ecu took a dump or a bad ground.
    I am almost done putting the intake and all that back together after cleaning all the grounds.
    If it still dosnt work, then its ecu swap time.
    I just dont understand how it can go from doing everything i was telling it to do, to just being numb to fuel changes but yet still accepting various other commands like open/closed loop, timing, ect.
    Its one mean gremlin whatever it is. This has turned out to be a real PITA!

  11. #11
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    you dont got a exhaust leak sucking in air and lean out your sensors?
    My setup is a 356ci with a 260/268 (212/218 at .050 lift) duration cam with aluminium corvette heads and flat top pistons running 11.3 comp. ratio. with tuned port injection and vortec crank pick up and dizzy running a 411 pcm and 60lb bosch injectors, 1.6 ratio roller rockers. For transmission its a 4l65e built with the monster in a box mega ss kit. All in a 92 chevy ext cab 4x4 pickup with a 98 cab now installed with a third door! running only e85

  12. #12
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    I do have a slight leak at the collectors where the y pipe slips on but thats after the o2's and if it was that causing it, then cranking the fuel in the ve table should still have a effect on it shouldnt it?
    It was doing just fine until it just magically all went to hell after the drive over to my buddies house.

  13. #13
    Senior Tuner mowton's Avatar
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    I was thinking one or both of the injector grounds to start

    Ed M
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  14. #14
    Senior Tuner edcmat-l1's Avatar
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    Attachment 33085

    Easy fix. You had the MAF codes set to 'no error reported' so it wasn't in SD. This one should get you going.

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  15. #15
    Senior Tuner mowton's Avatar
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    Quote Originally Posted by edcmat-l1 View Post
    Attachment 33085

    Easy fix. You had the MAF codes set to 'no error reported' so it wasn't in SD. This one should get you going.
    See....its always the simple answer. Good catch Ed assumed again

    Ed M
    2004 Vette Coupe, LS2, MN6, Vararam, ARH/CATs, Ti's, 4:10, Trickflow 215, 30# SVO, Vette Doctors Cam, Fast 90/90, DD McLeod, DTE Brace, Hurst shifter, Bilsteins etc. 480/430

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  16. #16
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    Edcmat you are the man! Lol I have no idea why I had put no error in there! Must have been delirious when I finished the work on the car or something..
    would have been easy as cake to find if I would have just did a compare on the dtc screen
    between this car and all the others that I have in speed density.
    owell, my newb mistake is fixed and the car is tuned! Thanks again!

  17. #17
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    man I was just fixing to ask this same question with the very same problem. While I am tring to tune the ve table as soon as I would hit the throttle it would go lean. it would be fine at idle and in closed loop but in open loop it would go lean with any throttle at all. I checked and damn sure set the mass air to no error.
    1993 reef blue Mustang coupe
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    Fast 92/92 intake
    PAT G./ EPS Custom cam 230/234 .600”/.602” 112LSA +2 advance
    century Built 4l60e with Circle D 3500 converter
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  18. #18
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    Well just be glad you didn't end up tearing the car apart looking for vacuum leaks and bad grounds like I did lol

  19. #19
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    Quote Originally Posted by zman420 View Post
    Well just be glad you didn't end up tearing the car apart looking for vacuum leaks and bad grounds like I did lol
    Yea. for some reason on this camaro I just got if you set the po103 code to 2 and no mill light I still get a code for po103 and a service vehicle light not a check engine light. I think this is a first. The car is a 2002 z28 camaro is that normal?
    1993 reef blue Mustang coupe
    Ls1 conversion
    1 7/8 cooks headers
    AFR 205 heads
    Fast 92/92 intake
    PAT G./ EPS Custom cam 230/234 .600”/.602” 112LSA +2 advance
    century Built 4l60e with Circle D 3500 converter
    4.11 gears

  20. #20
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    I have the same car. Just uncheck the ses boxes that deal with the maf. But make sure the actual code is "no mil light". Should turn off the light.