[Diy_efi] Flap-type Airflow Meters

Sun Jan 21 14:32:58 UTC 2007

I am adding an RS-232 port to the MAF interceptor so folks can customize
this mapping any way they wish. The incoming GM MAF frequency will be
linearly mapped to 256 table locations (in flash) what you put in those
table locations (desired voltage output) is up to you... i.e. I have
neither the resources or the desire to pick up and MAP frequency to
volts for this. The MAF interceptor itself can be used to assist in the
mapping - build a poor-mans flow bench with a fan suitable for pushing
say 1000 CFM, duct that through your flapper MAF and then through the GM
MAF. The interceptor reads out voltage from the flapper and frequency
from the GM - use a variable speed control on the 'flowbench' fan and
voila you should be able to map voltage to frequency across a broad
range... The GM MAF I already have a decent map of frequency to
gm's/second...

Hz	Grams/Second
4500    25
6000    50
7500    100
8500    150
9500    200
10000   250
10750   300
11250   350
11750   400
12000   450

On Sun, 2007-01-21 at 14:21 +0100, Torbj?rn Forsman wrote:
> 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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