『1990 Miata Air Flow Meter: OEM MAF Replacement and Testing Procedures』Related information(flow rotameter|digital flow meter|balo meter|hydraulic flow meter|volumetric meter|positive displacement meter|pitot tube flow meter|displacement meter|cfm meter|variable area flow meter|inline flow meter|differential pressure flow meter|calibrated flow meter|velocity meter|paddle wheel flow meter|oval gear flow meter|anemometer hvac|multiphase flow meter|doppler flow meter|thorpe tube flowmeter|heat flow meter)
1990 Miata Air Flow Meter: OEM MAF Replacement and Testing Procedures
Quick Answer
The 1990 Mazda Miata uses a vane type air flow meter, not a hot wire MAF. You can test it with a digital multimeter before you buy an OEM replacement. Release the wire clip. Do not unscrew the two small screws on the connector body.
Most lean misfire and hard start problems on this car come from cracked intake ducting or a damaged AFM connector. A tested OEM AFM often works better than a cheap aftermarket MAF on the 1.6L B6ZE engine.
What the 1990 Miata AFM Does
The 1990 Miata 1.6L engine has a swinging door air flow meter. The ECU reads the door angle as a variable resistance. This signal sets fuel injection time. The AFM also contains an intake air temperature sensor and a fuel pump cut contact.
Mazda calls this part an AFM. Many owners call it a MAF. The 1990 to 1993 Miata does not use a hot wire MAF. The 1994 and newer 1.8L engines use a hot wire sensor. That difference matters when you order parts.
Signs of a Failing AFM
A bad AFM can cause hard start, lean surge, hesitation between 3000 and 4000 rpm, and cold stalling. Some cars show black smoke if the ECU runs rich from an unstable signal. On OBD I cars, the ECU may store Code 8 as an airflow meter signal fault.
Do not replace the AFM before checking the intake tube. A split rubber elbow after the AFM lets in unmetered air. That creates lean idle faults that look like a bad AFM. We have seen a good AFM replaced for this reason on customer sites in Southeast Asia.
Testing the 1990 Miata AFM
Disconnect the negative battery cable. Release the wire clip from the AFM connector. Pull the connector off by hand. Do not unscrew the two Phillips screws on the connector. They hold the terminal block to the circuit board. Removing them can break the solder inside the AFM.
Set the multimeter to resistance. Measure the intake air temperature sensor across the THA and E2 terminals. At 20 degrees Celsius the reading should be around 2.21 to 2.69 k ohms. At 60 degrees Celsius it drops to about 290 to 354 ohms. An open circuit means the thermistor is bad.
Check the fuel pump cut contact next. With the AFM door fully closed the contact should be open. Open the door a few millimeters and the contact should close. A stuck contact can cause no fuel after cranking.
Measure the variable resistance across the Vs and E2 terminals while you slowly move the AFM door by hand. The reading should change smoothly. Look for jumps or dead spots. A flat reading or infinite resistance means the AFM is bad.
Reconnect the harness and battery. Backprobe the Vs signal wire with the ignition on. The voltage should move with the A
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Replacing the OEM AFM
The replacement is direct for most mechanics. Disconnect the battery. Loosen the clamp at the air filter box. Loosen the clamp at the intake tube. Remove the vacuum hoses if present. Unclip the harness connector. Fit the replacement AFM into the intake path. Tighten the clamps and reconnect the harness. Start the engine and check for idle roll.
For a 1990 Miata, the OEM part number is often B61P-13-210 or an exact Mazda replacement. A used AFM from a 1990 to 1993 Miata can work, but test it first. Cheap aftermarket MAF units often have poor calibration curves for this engine.
Industrial Flow Meter Note
This Miata AFM is a volume based flap meter. It is not a process mass flow meter. The test method is similar to analog flow signal checks we do in the field. Industrial flow meters usually output a 4 to 20 mA HART signal instead of a 0 to 5 V DC signal. Silver Automation Instruments supplies Coriolis mass flow meters, thermal mass flow meters, electromagnetic flow meters, and other process instruments for gas and liquid lines.
If you need a flow meter for an engine test cell air line, fuel blending skid, or compressor air measurement, send us the pipe size in DN, pressure in bar, temperature in Celsius, and flow range in kg/h or m3/h. Contact Silver Automation Instruments at Tel: +86-135-1213-1526, WhatsApp: 86-135-12131526, or WeChat: +86 13512131526.
FAQ
Is the 1990 Miata AFM the same as a mass air flow sensor? No. The 1990 Miata uses a vane type AFM. It measures intake air volume through a swinging door. A hot wire MAF measures mass directly.
Can I use a 1994 to 1997 Miata MAF on a 1990 Miata? Not directly. The electrical signal and the ECU map are different. The stock 1990 ECU expects the AFM signal.
What happens if I remove the two small screws on the AFM connector? You can pull the terminal pins out of the circuit board solder joints. The AFM then fails or becomes intermittent. Always release the wire clip instead.
How do I know if the AFM or the fuel pump relay is causing a no start? Check the fuel pump cut contact in the AFM. If the contact closes when the door opens and the pump still does not run, check the relay and the circuit opening relay.
Does Silver Automation Instruments sell a 1990 Miata AFM? No. Silver Automation Instruments sells industrial process flow meters for gas and liquid applications. For a 1990 Miata AFM, use an OEM Mazda part or a tested used unit.
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