Upgrading 1984 - 1987 Mass Air Flow Meters

WARNING: No warranty on this information. No responsibility accepted for blown up engines, computers, AFMs etc

Earlier Z31/CR31

1. Locate the op amp surface mount board in your ECU

2. Remove pin 5 on LHS and pin 1 on RHS by applying heat to the top of the connector and then pushing away from the mini board with a flat blade screw driver. Then using tweezers to hold the connectors, heat the opposite side of the circuit board to remove the connector completely.

3. Solder a jumper wire on the reverse side of the ECU to where you removed the jumpers

4. Verify continuity at pin 40 of the HD46510 A/D converter that against pin 31 of the ECU

HR31 / Y31

1. Locate the HD46510 Analog/Digital converter chip and the OPAMP board in your ECU

2. Get a multimeter and set it to 'continuity mode' so it buzzes when there is a closed circuit

3. Put one probe on the ECU connector pin 31. This is for the MAF input 

4. Use the other probe to locate the connection on the OPAMP board. It will buzz when you have the right pin

NOTE: Use Acetone or IPA to clean the conformal coating from these pins before probing. Otherwise it will never 'buzz out'

Mark this pin with a permanent marker.

5. Locate the HD46510 A/D chip. This takes the translated MAF voltage as a 0 - 5 volt signal on pin 40.

Clean around the pin as before and put the probe on it.

7. Using the same method as before, probe each pin until it buzzes out and mark that

8. Mark them on the bottom side of the PCB for later reference

(On the HR31 ECU I had pins 7 and 8 used for the MAF)

9. Use a desoldering gun and remove the solder from both pins.

10. Cut the pins from the board on the top side

11. Bridge the two pads together with solder

12. Use your multimeter to check continuity from ECU pin 31 to HD46510 pin 40

MODIFY YOUR MAF

5. Get the pinouts for your AFM. The RB30 and VG30 AFM pinouts are different

RB30 AFM pinouts

1. Sensor ground
2. Chassis ground
3. AFM output (2-7 volts actually...)
4. Hot wire cleaning
5. 12 volts from ECCS relay (ignition)
6. Calibration pot

Note: VG30 is different. Check against your service manual

6. Wire in your new AFM to map correctly

See http://paulr33.skylinesaustralia.com/diagrams/airflow-meter-wiring.html for most common Nissan AFMs

Notes:
- On the RB30 the sensor ground and chassis ground are the same. I connected the RB25 grounds together
- Hot wire cleaning is not used on later AFMs. Leave this wire disconnected (it is heated for 1 second after vehicle travels over 20kph when igniton powered off)
- Calibration pot wire from the ECU will either need a variable resistor or resistors matched close to 382 ohm added. This is wired against ground

7. Now  install your new AFM. For this test I used a piece of intake from a Ford with 85mm diameter one side (RB25 AFM is 80mm) and 70mm the other side. Obviously a wider intake all the way through to the inlet manifold would be best.

8. Monitoring: Check pin 40 on the HD46510 when the new AFM installed and running is between 0 - 5 volts if you can get your car running after tuning or monitor with NIStune

NIStune SPECIFIC TUNING

9. Turn on the ignition and click USB Consult inside NIStune.

Download your maps using the PC sync button

10. Open up the VQ map and K Constant windows

11. Under operations menu, change the Mass Airflow Meter

12. This will change your AFM map setting and global fuel adjustment (K Constant) based on HP figures inside NIStune.

The HP figure for some vehicles are approximations, so K constant may need to be tweaked further.

From the comparison you can see how these have changed:

13. Next connect up your wideband, start the vehicle and adjust K constant until air fuel mixtures are correct.