AFM revival for 8v and V6
I've been looking into this for a while and have quite a lot of info on the Bosch Motronic AFM.
The main problem with them is the contact strip inside the meter becomes worn as the sliding mechanism wears away the electrical contact surface. This will give erratic voltages and affect the fuelling of the engine. The lambda probe will "iron" out this problem to a certain degree, but it doesn't do it instantly. During my testing, if I had the mixture too rich or too lean, the AFM voltage would take a few seconds to stabilise and sort out the mixture. Imagine the affect of this few seconds as the throttle postion is constantly moved during normal driving !!!!
Anyway here goes:
To test if the AFM contact strip is OK, connect a voltmeter between pin 2 and ground. With the engine idling, you should see a nice smooth reading. Gently open the throttle - the voltmeter should rise accordingly. If it's diving about, the flow meter needs attention.
If the contact strip is suspect, you can do a little modification as follows:
Carefully prise off the black cover on the bottom of the AFM. It's held in place with strong sealant. Inside you will see the contact strip and the wiper arm which is connected to the flap of the meter. Undo the screw that holds the wiper arm in place (note the position of the arm at rest so you can put it back in position afterwards). Undo the 4 screws that hold the rest of the black plastic housing in place. You will now have access to the plate with the contact strip. Remove the 3 screws and carefully remove the plate.
You will see the contact strip is scored by the wiper arm. The idea is to reposition the plate so the wiper has a fresh bit of track to run on. I used a small file and "ovaled" the screw holes so I could slide the plate up or down a bit so the wiper was on a fresh bit of track. Put it back together and check the wiper is on fresh track for the whole of it's movement.
OK, now you have to calibrate the AFM !!!!!
Put the AFM back on the car and connect the cable. Put the AFM on upside down so you can access it's internals. Run the engine until it's warm. Disconnect the signal plug for the lambda probe but the leave the heater wires (the white ones) connected. Measure the voltage of the lambda at idle. You want it to be between 0.35 and 0.65 volts (ideally 0.5 volts). The voltage may fluctuate a little (mine was between 0.4 and 0.5 volts at idle after adjustment). If the voltage is too high, it'll be rich, too low and it'll be lean. If you need to adjust this, loosen the screw that holds the wiper arm and move it gently up or down to adjust the voltage. Once the desired voltage is obtained, stop the engine and carefully tighten the screw up, making sure you don't move it or you'll have to do it again.
So that's the AFM set at idle. What about on the move ???
Start the engine and open the throttle by hand to say 3000rpm. You'll see the voltage from the lambda reach about 0.9 volts as the mixture richens for acceleration. Hold the revs at 3000 and the voltage will settle. Again, you are looking for about 0.5 volts, if not you will have to alter the spring tension. You do this by moving the big black platic wheel. Increase tension to bring the voltage down and decrease the tension to bring the voltage up. Do this with the engine off and only move it ONE cog at a time. After each adjustment, start the engine and check the voltage at your selected higher revs.
Once this is done, replace the cover and put it all back together properly....FINISHED !!!!
I've done over 140miles in the V6 since doing this and the biggest difference is how smooth the car is. Even changing gears is smoother as the revs don't drop away so quickly like they used to.
Like others, I'm not responsible for any damage/loss/death etc etc that occurs from these instructions.
Good Luck...................BOOOOOOOOOM !!!!!!