Z31 Air Flow Meter
The Air Flow Meter measures the mass flow rate of intake air. Measurements are made so the control circuit emits an electrical signal in relation to the amount of heat dissipated from a hot wire placed in the stream of air.
The air flowing around the hot wire removes heat from it. The temperature of the hot wire is very sensitive to the mass flow rate of the air. The higher the temperature of the hot wire, the higher its resistance. This change in temperature or resistance is determined by the mass flow rate of air.
The control unit regulates current (I) in relation to the varying resistance value (Rh) so that voltage (Va) always equals (Vb). The Air Flow Meter transmits the output for voltage (Va) to the control unit (ECM) where it is converted to an intake air signal.
*WARNING* - Do this modification at your own risk. We Are not responsable for any issues of your own doing.
Differences
There were two different Air Flow Meters (MAF) used on the Z31: "Adjustable (FED - Yellow Sticker)" and "Not Adjustable (CAL - Blue Sticker)". The differences are explained below.
Adjustable (FED - Yellow Sticker)
Behind the "Seal Plug" is a variable resistor (potentiometer or POT). While this is called a “variable” resistor, it actually sets the constant resistance on wire #31, which sends the MAF signal back to the ECU (Ra and Rb in diagrams). You can manually adjust this resistance by removing the plug and turning the resistor, as shown here.
Non Adjustable (California Smog Blue Sticker)
On the California-spec (blue sticker) MAF, pin #30 at the ECU connects to an Exhaust Gas Temperature (EGT) sensor instead of a variable resistor. This means the “constant resistance” is always changing based on actual EGT. Yellow sticker (federal) MAFs only change if you manually adjust them, while the blue sticker MAFs vary with exhaust temperature. To modify the blue-sticker MAF’s resistance, you would need to physically access the circuit.
Common Problems
- Can not rev above 2000rpm
- Fouling out plugs (rich)
- Black smoke
Troubleshooting
To test, measure the resistance (Ohms) across the terminals. If there is no connection (open circuit) between any of the pins, the MAF may be faulty.
| Terminals | Resistance 1 | Resistance 2 | Resistance 3 |
|---|---|---|---|
| A - B | 663 Ω | 609 Ω | 580 Ω |
| B - C | 72 Ω | 73 Ω | 72 Ω |
| C - D | 0.9 Ω | 0.9 Ω | 0.9 Ω |
| D - E | 1.68 kΩ | 1.75 kΩ | 1.74 kΩ |
| E - F | 11.1 kΩ | 11.1 kΩ | 11.1 kΩ |