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What controlls the A/F ratio once warmed up?

Discussion in 'General Tech and Maintenance' started by phyregod, Aug 5, 2005.

  1. phyregod

    phyregod !!YTINASNI

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    Well, my car is surging again. After it is warmed up, it surges between 750 and 900 rpm. The air fuel is going rich to lean with the surges.

    DONT tell me that the air fuel guage is a lazer light show.

    I went through everything that had anything to do with the idle and fixed/inspected it. It was fine for a while but is now back. What controlls idle and idle mixture once warmed up?

    I've tried switching ECUs just to be sure, and it did the same thing.

    Ideas?
     
  2. B16RacerN2NR

    B16RacerN2NR Working Hard VIP

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    bleed the head for any air pockets
     
  3. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    O2 sensor with the ECU controls the air/fuel ratio, but that's probably not what's causing your surging problem.
     
  4. 4DRB16A

    4DRB16A Senior Member

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  5. pissedoffsol

    pissedoffsol RETIRED

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    aside from the problem, this is how efi cars run.

    the ecu gives it gas until it gets to a certain richness. then it cuts it. when it gets to a certain lean point, it adds fuel. and thus repeats. this happens 100s if not thousands of times a second, and it appears to us to idel steady.



    you're right, it isn't. laser is spelled with an S, not a Z :)

    but that aside, the narrow band a/f gauges are slow to react, and what you are seeing is the back and forth action. this is normal. at 0 throttle, it SHOULD go back and forth.



    but, you have a problem. :)

    90% of the time, if you aren't throwing a code, its air in the coolant system.
    bleed it.

    easest way is just let it boil over with the cap off. squeeze the upper hose slowly, and get the air pockets out (make sure the car is warmed up first, and has passed coolant past the water pump)

    another problem could be timing issues. throw it on a timing light, make sure you're at base 16* at idle... might be hard to judge with the surge, but you can probably get a full revolution out of it before it dips.

    the fast idel could be the issue (the link posted above) but if it was runing good befre, and just started doing this, chances are, thats not the problem. what the link describes is a common problem first start up after swap or something. but it could be. can't hurt to try it.
     
  6. phyregod

    phyregod !!YTINASNI

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    I'm going to try everything again.

    I've bled the coolant.. like 5 times now.
    Tightened up the FITV, also tried a different one.
    cleaned out and checked the EACV
    triple checked all vacuum hoses
    calibrated the TPS
    new oxygen sensor
    swapped computers

    but like you said, I still have the problem. Or, the problem is back.

    Time to do it all over again I suppose.

    Not throwing codes BTW, of course it couldn't be that easy. Ah well..
     
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