Another Afm Question

[mad082]

when the AFM is dirty (rb25) does the car run leaner or richer?

i thought it would run leaner as it wouldn't read as much airflow, but i read somewhere that it runs richer due to it taking more voltage to keep it hot.

[Sydneykid]

when the AFM is dirty (rb25) does the car run leaner or richer?

i thought it would run leaner as it wouldn't read as much airflow, but i read somewhere that it runs richer due to it taking more voltage to keep it hot.

My experience has been that there is no consistency, at low airflows they seem to run leaner but at mid range airflows (boost building plus a bit) they run richer. Then at high rpm they go lean again.

It also seems to depend on why it is dirty, 100% oil is a better insulator than oil contaminated with dirt/dust.

The true sign of as dirty AFM is inconsistent and non linear readings. For example rev it to 2,000 rpm and it shows 3 volts, then the next time you rev it to 2,000 rpm it shows 1.7 volts. Or rev it to 3,000 rpm and it still shows 2 volts. That’s how I pick a dirty AFM.

cheers

Edited September 14, 2006 by Sydneykid

[otto]

when my afm gets dirty mainly from the oil on the pod filter it runs rich ie, when its clean at idle it will read 1.6-1.5 on the safc but when its dirty it will read 1.9-2.4 this seems to take me maybe 2 or 3 months to happen and by this point the car will also r&r under acceleration and hunt at idle sometimes completly conk out when things are real bad. but give it a quick squirt with electrical contact cleaner and it goes back to 1.5 and runs sweet! I think it has something to do with the dirt or oil reducing the resistance of the resistor in the afms hotwire maybe by letting current pass around it and with a decrease in resistance theres gonna be an increase in output voltage without an actual increase in airflow hence run richer...GOSH i hope i got that the right way around.

Ps. i cant remember weather those figures i gave on the safc readout were percentage readout or voltage i think they were a percent but you get the idea anyway.

Edited September 14, 2006 by otto