Hello
I have a MAF from 1990 with an adjusting screw.
how much ohm has to be set between pin 1 & 6?
at the moment it is set to 650 ohms
Thanks
Thanks
There is no pre-defined setting for MAF sensor. Those were adjusted on the car to match 1-2% CO at 800rpm (idle). Potentiometer was installed since 87 in XJS (non-CAT). It cheats the heater a little bit. Increasing resistance will bring voltage on the hot wire down making it cooler (more fuel injected as higher air flow is simulated)… Or maybe other way around 
Before you’re going to fiddle with it - use a lot of WD40 or you’ll snap it off internally.
This should be done only with gas probe in your exhaust pipe to get to the required 2% or slightly above that (for non-CAT only).
My advice - run rich.
I have the same Lucas/Hitachi 5AM AFM on my MGB V8 (Land Rover 3.9)- if using the oxygen sensors, you adjust it to 1.8 volts with ignition on, but not running.
If running open loop mapping, it ends up 1.3 to 1.4 volts.
I assume it would be similar voltages as displacement is similar.
Hello. where can I measure the voltage while idling?
At the AFM connector; back probe the black/red (signal ground) and blue/red (idle trim). Have to use sharp probe to get through the weatherseal where the wires come out. I used furniture sewing needles…
Don’t know if your wire colors are the same, I can look later today for the wire positions in the connector.
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Hi.
thanks for the help,
it should be GK (green / pink)?
then you measure against earth and then when the engine is idling and the engine is warm, there must be about 1.3-1.4volt?
No, idle trim which is Green/red according to your diagram and signal ground (black/yellow on your diagram).
The AFM signal measures .3v with key on, and measures 1.5v idling if I recall.
ahh okay, I slipped. the 1.5v at idle with a hot engine? if I am not connected to the 1.5v then turn the screw on the MAF … do you know whether less volts is fatter or leaner,?
No. The potentiometer only directly adjusts the idle trim (green/red) measured to signal ground. It has a slight affect on the AFM signal to about half throttle.
The AFM signal (Green/pink on your diagram)is in relation to airflow; ignition on not running should be .3v; it will go higher (1.5-1.8v at idle and close to 5v at full load, high rpm) as the engine starts. If it doesn’t, you may have a dirty or failed air flow meter.
As far as idle trim, lower is richer and higher is lean.
okay, and what can I adjust on the screw on the MAF ???
If you have oxygen sensors, 1.8v. If you do not have oxygen sensors, start at 1.4v. If it hesitates, adjust a little lower (1.3)
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