Sensor Information

(AFM) Air Flow Meter

The Air Flow Meter measures the mass flow rate of intake air. Measurements are made in such a manner that the control circuit emits an electrical signal in relation to the amount of heat dissipated from the hot wire placed in the stream of air.

The air flowing around the hot wire removes heat from the hot wire. 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 value is. This change in the temperature or resistance is determined by mass flow rate of the 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.



Common Problems

• Can not rev above 2000rpm
• Fouling out plugs (rich)
• Black smoke

Troubleshooting:

To test mesure the Ohms across the terminals. If there is a no connect between any of the pins, then you have a problem.

Ohm readings across all the terminals.

• A-B : 663 / 609 / 580
• B-C : 72 / 73 / 72
• C-D : .9 / .9 / .9
• D-E : 1.68k / 1.75k / 1.74k
• E-F : 11.1k / 11.1k / 11.1k

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(TPS) Throttle Position Sensor

The TPS is attached to the Throttle Body with 2 screws. It monitors the movement of the accelerator pedal. The switch has an idle contact and a full throttle contact. The idle is closed when the throttle is set to idle and opens when at any other position. The full throttle contact is only used for the Electronic controlled automatic transmission models as a kick down switch.

Common Problems:

If your car lurches a little while coasting in gear towards a red light, it may be that the TPS is not quite right and the computer is switching from idle to running. This can make your car lurch a little because the fuel is shut off when you are coasting in gear to save gas. The switch is opening and closing, turning the fuel on and off. To replace the switch, simply remove the two screws, unplug it, and replace it with the new one.

ECU Code #23

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(FPR) Fuel Pressure Regulator

The fuel pressure regulator(FPR) is the small metal can in front of the intake manifold on the centerline of the engine with a vacum hose coming out the top. This vacum signal is controlled by a vacum solenoid located beside the ignition coil on the driver's side fender. The vacum is on at all times except for hot starts, when the vacum signal is removed from the FPR, raising fuel pressure and making hot starts easier. The regulator is nothing more than spring loaded diaphram, the spring keeping the appropriate amount of pressure in the fuel system. The fuel flows from the fuel pump into the injector rail(from the rear) and the regulator bleeds pressure off the front of the rail and returns it back to the fuel tank.

Common Problems

The only real way the regulator will fail is when the diaphram gets old and cracks.

Trouble Shooting

The easiest way to check for this is to pull the vacum hose off the top of the regulator and rev the engine. If the regulator is bad, fuel may squirt out the vacum port, meaning the diaphram is broken. When the diaphram fails, fuel is sucked into the intake and the engine runs extremely rich, making a bluish smoke in the morning. Some of this leaking fuel will get sucked into the crankcase through the pcv system, making your oil smell like gas.

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(CAS) Crank Angle Sensor

The crank angle sensor is a Basic signal sensor for the Entire E.C.C.S. It monitors engine speed and piston position, and it sends signals to the E.C.C.S. Control unit for control of fuel injection , ignition timing, idle speed, fuel pump operation and EGR operation. It is located inside of the Distributor under the rotor.



Common Problems:
Code #11

Troubleshooting:


If restance in step 1 is not 0 then replace the harness. If voltage in step 2 is not 12v then check the EFI relay and the Harnes power lead.

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Idle-up solenoid (Non-Turbo only)

The Idle-up solenoid valve is attached to the intake collector. The solenoid valve actuates to stabilize idle speed when engine load is heavy because of electric load, power steering, oil pump, ect.



Common Problems:

Stalling when Accessories are running

Troubleshooting:

To test do the following:

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(A.A.C.) Auxiliary Air Control Valve)

The (A.C.C.)Auxiliary Air Control Valve is attached to the right side of the intake Manifold. The E.C.U. actuates the A.A.C. valve by an ON/OFF pulse. The longer that ON duty is left on, the larger the amount of air that will flow through the A.A.C. valve.



Common Problems:



Troubleshooting:

To test do the following:

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(CHTS) Cylinder Head Temperature Sensor

The Cylinder Head Temperature Sensor is located in the right side head behind the timming cover. It monitors changes in cylinder head temperature and transmits a signal to the ECU. The temperature sensor is a thermistor that is sensitive to the change in temperature. Electrical resistance decreases as temperature rises.



Common Problems:

Missing or backfiring on cold starts. ECU Code #13

Troubleshooting:

To test do the following:





Here is a shortcut for removal that was posted on Z31.com

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Knock Sensor or Detonation Sensor (Turbo Only)

The Detonation Sensor is attached to the cylinder block and senses engine Knock conditions. A knocking vibration from the cylinder block is applied as pressure to the piezoelectric element. This Vibrational signal is then converted to a voltage signal which is delevered as an ouput signal.



Common Problems:



Troubleshooting:

To test do the following:

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Oil Pressure Sensor

An Information relay unit for the indicator light or gauge on instrument panel. It contains a diaphragm that responds to changes in oil pressure. When the oil level is over a pre-set limit, the diaphragm opens the switch, turning off the light. When level is below the pre-set limit, the dash light comes on. In later model cars, if the oil pressure drops, the switch turns off the fuel pump, to stop the engine and limit damage to internal parts. Oil pressure switches can be grouped into two categories, units for electrical gauges and for mechanical gauges. The Z31 uses a electrical Sensor.



Common Problems:

Oil Pressure gauge will read low or not at all

Troubleshooting:

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Air Regulator

The Air regulator gives a air by-pass when the engine is cold for the purpose of a fast idle during warm-up.

The Air Regulator is made of a bimetal, Heater and a rotary shutter. When the temperature is cold the air by-pass port is open. As the engine starts, an electric current flows to the heater and the rotary shutter closes off the by-pass port. It remains closed till the engine stops and the temperature is once again cool.



Common Problems:

Sluggish on cold starts

Troubleshooting:

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Sources Used on This Page: 1984-1988 Nissan 300ZX Factory Service Manual, Z31.com