1uz running better with AFM unplugged

Discussion in 'Diagnostic & Repair Tech' started by Jay351, Sep 18, 2017.

  1. Jay351

    Jay351 New Member

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    Hey everyone,

    I have been doing some searching but I still feel the question I have has not been directly answered.

    Im running a 93 ls400 1uz in my 91 hilux. Im running the factory ecu. With everything plugged in the truck runs pretty good but at around 3800rpm at it seems to gain noticeable power all the way up to redline.

    When I unplug the AFM the truck has amazing power from way down low all the way to redline, it feels much smoother and seems to run better. Aside from it running rich.

    So far I have Adjusted the TPS, replaced the water temp sensor, cleaned the primary o2 sensors, tested the AFM, replaced the caps in the ECU.. nothing seems to help.

    Now I am currently running no sub 02 sensors and no EGR, so the ecu usually has three codes for those.

    My question is, what sensors are ignored once the AFM is unplugged? Something must be pulling alot of timing out because this is a very noticeable amount of power being lost/gained. Any suggestions from the veteran 1uz people out there?
     
  2. Jay351

    Jay351 New Member

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    I forgot to mention. When the engine is cold and the AFM is plugged in, it runs very similar to once its warm and the AFM is removed.

    Im running an oem toyota thermostat with a giant aftermarket aluminum radiator and a 16" puller fan. Could it be running too warm?
     
  3. eicca

    eicca Member

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    Bump for more experienced people than me.

    My first guess is to try another AFM for good luck. With the AFM unplugged it defaults to preset fuel maps, which you probably know. It looks like there is an air temperature sensor in the '93 AFM, and my guess is that it's pulling timing because it's getting a falsely high reading.

    My next guess is that the ECU doesn't like having the EGR/secondary O2s missing, but I would expect the power loss to be on the high end, not the low.

    Too bad it's not OBDII or this would be a whole lot easier.
     
  4. Jay351

    Jay351 New Member

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    Thanks for the reply!!

    So recently I began to modify my y pipe to add the secondary o2 sensors, although they are only two wire sensors. This should be done in the next week or two depending how cold it gets in my shop.

    I also tried running the truck with no hood to eliminate potential false high readings for temperate due to ambient standing air, no difference.

    I'm going to grab a spare afm from my friends parts car and will throw that in after I'm done with the exhaust.

    As far as the egr, I will throw in a resister to trick the computer but I doubt it would have this drastic of an effect as I'm experiencing.

    In addition I swapped in another throttle body and will try adjusting the tps on this to confirm it's not the issue.
     
  5. cribbj

    cribbj "Supra" Moderator Staff Member

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    Try a different coolant sensor as well.
     
  6. Jay351

    Jay351 New Member

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    Should I bother going oem?
     
  7. eicca

    eicca Member

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    Coolant sensor. Forgot that one. Always go OEM if you can.
     

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