Vane Air Flow Meter

Part 3 - 25th Nov 03 

Flap Tension

The air flow meter is often thought as a air intake restrictor and many attempts to fiddle with it in hope to have more power, more responsive, more fuel hence more powerful etc.

However ....... this is a controversial thinking. The engineers who invented it would have made the necessary compensations in the ECU to counter the lost of energy used by the initial stage to push the flap open???

May be they did, may be they did not.

However, this article is to supply sufficient information regarding to the "fiddling" of AFM. heheeh

Normally one would hold the tension lock open and force the ring-gear to turn a few click (counter clock-wise) to reduce flap closing tension. This is hoped that with less closing tension, it will require less air momentum to open the flap and hence be more responsive and more powerful etc.

However upon one stage the tension will be too loose and cause the fuel pump engage pin to fail, which lets the fuel pump to turn on upon key-ON, which is incorrect.

This can be remedy by release the needle's allan key lock and turn in counter clock wise a little to reposition the needle back to it's original position.

But............ since there is not enough tension to maintain flap closure, therefore after re-positioning the needle, it does not have sufficient strength to push the fuel pump engage pin open. Hahahahahahh what a contradiction.

The initial position of the needle may be used by the ECU to perform some compensation - it is vital that it is where it should be???

Whoever the inventor of AFM is??? salutee !!!!!!! hahahahhahahha

I know if I were the engineer, I would make the ECU take into considerations the followings before starting the car.

  1. water temperature
  2. air intake temperature
  3. for D-jetronic perhaps MAP sensor ................... no! there is no vacuum before engine start and must be ignored........
  4. however for AFM it is important to take a before engine start needle position, as this would act as a calibration technique.
  5. TPS, again to act as a calibration system - but it is known that this does not exists.
  6. and others?


Regardless, all kinds of combination have been tried and is no good. i.e.

  1. Flap - 1, Needle 0 - Engine feels lighter :)
  2. Flap - 2, Needle 0 - Even lighter feel :)
  3. Flap - 3, Needle 0 - fuel pump engage pin start to touch, engine responsive
  4. Flap - 3, Needle - 3 - Dull
  5. Flap + 2, Needle + 3 - Dull
  6. There were more, but forgot.

To whomever going to use this information, 

  1. Please mark down ring gear original position. 
  2. Please also remember to mark down where the needle rest originally. 
  3. Please also mark down how many mm does the fuel pump engage pin manage to push apart
  4. Please also mark down how tight is the flap when force open a little and let go softly like engine shut down. This is important to see under soft release condition if the returning arm is able to force the fuel pump engage pin to disengage.


Key Words References: -

  1. Flap - 1 = less tension one click counter clock-wise (flap open easy)
  2. Flap + 1 = Increase tension one click clock-wise (flap open difficult)
  3. Needle - 1 = Re-position needle 1mm clock-wise (ECU see flap open less)
  4. Needle + 1 = Re-position needle 1mm counter clock-wise (ECU see flap open more)


  1. AFM Breakdown
  2. Dismemberment
  3. Flap Tension
  4. Engine Warning Light On
  5. Warning / Tips - Buy Vane Air Flow Meter (AFM)



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