I have a good condition AFM from a 86 1g gte with part number 22250-70170. My 3rd gen 1g gte uses 22250-70200 which is obviously a newer number. Seems like there is no difference on the housing itself, and I measure the resistances across terminals and compared them, both are very close with each other. However, the air bypass screw depth seems to be differently adjusted. Measured from the top of the screw housing to the screw head, the 86 AFM has a distance of 19.5mm and the 89 AFM is 17mm. The 89 model has bigger air bypass opening. This is of course assuming that this bypass screw was never tampered with on both units. So my questions :
1. Since resistance values are the same, and assuming the air bypass screw wasnt tampered with, would backing out the bypass screw on the 86 AFM to 17mm depth allow me to use it in my 89 1g gte ?
2. Anyone knows the factory spec depth for 2nd gen vs 3rd gen AFM ?
3. If i just plugged in the older AFM on the 3rd gen 1g gte, would there be any adverse effects (running lean/rich or rough)
I am gonna answer this since I just found out. These 2nd and 3rd gen 1g gte run a Vc E2 of 5V, which slides downwards the more the flap is open.
Vc or Voltage constant is the 4th pin on the AFM plug, E2 is the 5th pin, Vs or voltage Slide is the 6th pin, and 7th pin is THA or temp sensor.
The voltage in Vc(+) to E2 (-) with ignition on engine not on, is about 4.75 V. The Voltage on Vs(+) and E2 (-) is 4V with the flap closed, and this voltage drops down to a very low value when flap opened to a maximum.
This was measure off the newer 22250-70200 AFM.
Now I hooked up the 2nd gen older AFM 22250-70170 and found the Vc to E2 is also 4.75V, but the Vs to E2 at closed flap is 3.75V, that means the engine will run richer from the get go. I knew this would happen so i tightened up the flap spring quite tight to open the door less, but still to no avail, I could smell the over fueling in the exhaust fumes, its running too rich. I cant tight up the spring much more as the flap might not open enough to keep Fc and E1 in contact for the fuel pump to activate at idle.
So in summary, you can run a 3rd gen AFM on a 2nd gen engine by weakening spring tension to compensate , but not a 2nd gen AFM on a 3rd gen engine in which the start voltage is lower from the get go making the ECU think there is much more air than its receiving.
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