[Diy_efi] Flap-type Airflow Meters

[Torbjörn Forsman]

Hi!

Beware that there are no two types of flapper AFMs that have the same 
calibration. Typically, those intended for microcontroller based ECUs 
(for example, Bosch Motronic systems, Toyota TCCS, Ford EEC-IV on 
european cars) have a relatively linear angle - to - voltage 
characteristic, while those intended for analog ECUs (Bosch L-jetronic, 
LE- and LU-jetronic, Lucas and various japanese L-jetronic clones) 
rather have a logarithmic characteristic.

The potentiometer on the PCB is divided into 10 or 12 sections with a 
laser trimmed parallel resistor for each section. Usually, there are 
also series resistors at both ends of the potentiometer.

On AFMs for L-, LE- and LU-jetronic, there is a connection to the ECU 
from a tap at the "hot end" series resistor, on LE and LU the air 
temperature sensor is connected in parallel to a part of this resistor.

All other AFMs have the temperature sensor connected from ground to a 
dedicated pin in the connector.

When discussing different AFMs, it is best to mention the part number 
(Bosch number) of the complete AFM (0 280 20x xxx), the part number of 
the hybrid PCB (1 288 31x xxx) and the number of the return spring (only 
the three last digits are stamped on the plastic spring holder wheel, 
very old AFMs may lack this number). It might also be interesting to 
note if there is an auxiliary spring that balances part of the main 
spring's force at idling position of the flapper.

Best regards

Torbj?rn Forsman

Steven P. Donegan wrote:
> Now - if someone can just map those steps to airflow numbers I can make
> a GM frequency MAF to flapper MAF voltage translation table. Which will
> allow those of you out there who want to run 80mm MAF's on your (pick
> engine) car :-) That circuit board is already built - that's my little
> MAF interceptor project...
> 
> On Fri, 2007-01-12 at 15:23 -0500, ScottyGrover at aol.com wrote:
> 
>>Dan was asking about these Bosch/Nippon meters and how they were
>>calibrated. 
>>I put 12VDC between pins 6 and 9 and hooked a voltmeter between pins
>>6 and 
>>7. I then rotated the toothed wheel on the end of the rotating shaft
>>and  this 
>>is what I read:
>>Base       1.29V
>>1 tooth     1.75V
>>2 teeth     2.7V
>>3    "        4.3V
>>4    "        5.3V
>>5     "       5.9V
>>6     "       6.5V
>>7     "       6.8V
>>8     "       7.3V
>>9     "       7.6V
>>10   "       7.95V
>>11   "       8.05V
>>12   "       8.2V
>>max         8.21V
>> 
>>I hope this helps.
>> 
>>Scotty 
> 
> 
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