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How-To: Air Flow Meter Adjustment

By: OldMage (oldmage@hotmail.com)

Shopping List:

  1. New AFM (If you screw this up)

Tools Required:

  1. Sharp knife
  2. Phillips head screw driver
  3. Pen or other permanent marker

Process:

A well-known technique used with AFM (Mass Air Flow Meter) sensors is to "fool" the EFI computer into thinking that there is more air entering the intake than there actually is. This results in a richer mixture and often, improved power and throttle response. Here's OldMage's explanation of how to do this for the 22RE:

Modding the AFM involves cutting the silicone seal around the black cover to gain access. Once inside, there's a "curly brace" looking metal clip in the upper left corner being held down by a Phillips screw. Mark with nail polish or similar, the original position of at least one of the ends. Then, WHILE HOLDING THE LARGE GEAR WHEEL, loosen the screw allowing the metal clip to go slack. Turn the gear wheel clockwise to lean the running mixture, and counterclockwise for richer. The idle mixture is largely unaffected by this adjustment. Do not adjust any more than 3 teeth in either direction with a stock system. Once you have the gear wheel where you want it, tighten the Phillips screw again to make the metal clip hold the wheel in place. Supposedly, a stock system shouldn't need any adjustment, and won't benefit much from changes. It's a tradeoff; leaner helps off-the-line, richer adds to the top-end.

You can adjust the idle mixture by carefully drilling out the aluminum plug in the lower right "corner" of the AFM near the outlet to the throttle-body. Tightening the screw beneath the plug makes the idle richer, loosening it leans the mix.

Another item to consider adjusting is the throttle-position sensor itself. It's the black square box on the driver's side of the throttle-body. There's 2 screws that hold it in place. Loosening them allows you to rotate the sensor. Clockwise advances the changes relative to throttle position. Too far and you'll "disable" the idle position. If you retard it too much, you'll go into lean misfire around 3000 rpm. It should go from idle setting to mid throttle around 2500 rpm, I think. I wish I had throttle-plate degree measurements or something more precise, but I don't. The plastic cover comes off so you can see the switch actions inside, which may help in adjusting it.

OldMage
83 Celica GT-S coupe
Portland, OR USA

oldmage@hotmail.com
http://www.speedtoys.com/~oldmage/

Article reproduced with permission from OldMage.
Copyright © 2001 OldMage.

Footnotes:

  1. Thanks to: OldMage

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