Ford EFI sensors overview

Last Updated on July 23, 2024 by Mutiara

A sensor is a device that checks a mechanical value and converts it into an electrical signal. It should not be confused with a switch. At times inputs will be referred toa s sensors, but this isn’t true. Some inputs have an ON state and OFF state, these are called switches. Switches come ON at a set value and do not indicate an actual value, simply greater or lesser than its switching level.

An important note is that the EEC operates a majority of the sensors at 5-volts DC. Hence, the alternator and batteries are not dependable for voltage supply when it comes to sensitive electronics. The automotive electrical system ranges from 10-14. Inside EEC is a voltage regulator, this steps the voltage down to a constant 5-volts. This voltage is called Reference Voltage. The sensors are supplied with this Reference Voltage and the sensor returns a variable amount of this to the EEC to indicate the status of the system the sensors is watching.

Some of the sensors need a special ground to get rid of the left over Reference Voltage that isn’t sent to the EEC as a status. The EEC also provides a 5-volt ground loop for these select sensors. This special ground is called Signal Return. The way this works is the EEC sends a 5-volt Reference Voltage to a sensor, the sensor sends 1.87 volts back to the EEC as the sensor status, and the rest of the voltage (which should be 3.13-volts) down the Signal Return.

The sensor system is very versatile. The ECC has programming that admits not all sensors are created equal. Once a new sensor is installed the battery should be re-attached, having been disconnected to begin with. The EECs Keep-Alive memory stores the sensor irregularities. Sensors are not all manufactured the same, there is a 15% tolerance from one sensor to the next one rolling off the assembly line. Once the battery is reconnected the KAM reads all the sensor baselines and and stores these as normal. It’s can be represented as an aerial picture of all the EFI system components. The EEC can now plug in a sensor reading compared to baseline for an accurate value. If the sensor (over time) starts to loss its sensitivity, the EEC will catch on (from its original memory) and begin to compensate for this. As the sensor ages and it’s readings get worse a fault code will be stored in the KAM memory. When trouble shooting a problem, codes should always be checked prior to disconnecting the battery, which erases the codes stored in the KAM memory.

Following is more in depth information about each sensor and how it works.

Air Charge Temperature sensor (ACT)

This measures the temperature of the air entering the engine. Which impacts the fuel ratio; the cooler the incoming air is the denser it is. Denser air can utilize more fuel, giving us even greater accuracy in obtaining our desired air to fuel ratio.

Barometric Pressure sensor (BP)

This sensor measures the pressure of the outside air. This allows you to drive from Death Valley, California to Denver, Colorado. Keeping fuel ratios perfect for each elevation along the trip. This is something carburetors could never do. Speed density systems re-use the MAP sensor to obtain this data prior to start up.

EGR Valve Position sensor (EVP)

This sensor mounted to the Exhaust Gas Recirculation Valve (EGR) monitors its position. The computer delivers less fuel and more spark timing when the EGR is open. Lowering fuel millage and tail pipe emissions.

Engine Coolant Temperature sensor (ECT)

This measures the temperature of engine, and has a great impact on fuel ratio. This makes simple work of enriching the mixture on start up, overheating, and full throttle fun. It also allows us to lean out the mixture at certain times, to shorten the time it takes to warm up the engine helping us get great fuel economy.

Heated Exhaust Gas Oxygen sensor (HEGO)

This sensor measures the oxygen content in the exhaust gas. This sensor is for feedback, it tells the computer when the air to fuel ratio is above or below 14.7:1. Sometimes the computer is attempting this mixture and sometimes it ignores the HEGO. For more, please seek further reading on the web or in books.

Knock Sensor (KS)

The knock sensor is used to detect engine detonation or spark knock. As a result, a voltage sent to the PCM which will retard spark timing.

Manifold Absolute Pressure (MAP)

This sensor measures the vacuum between the intake valves and throttle body. The manifold vacuum is cross referenced with engine temp in a table, plotting where the vacuum and temp meet in a table provides the basic air fuel ratio. For this system to work Ford had to measure the actual fuel requirements of the engine. Only used on SD systems.

Mass Air Flow (MAF)

This sensor uses a heated wire to actually measure the weight of incoming air. The cooler the wire becomes, means more air is passing it, into the engine. Once the mass of incoming air is known, calculating fuel ratio is almost perfect. The air mass is cross referenced with engine temp in a table, again plotting where in the table temp and air mass meet provides a basic fuel ratio. Only used on MAF systems.

Stator

This sensor tells the computer engine rotation. It sits under the distributor cap and picks up a signal from a wheel with teeth. The wheel has the same number of teeth as cylinders in the engine. The #1 cylinder tooth is smaller to identify firing order. This is the most important sensor. Without it working properly the computer never senses the engine moving and the entire vehicle is useless.

Throttle Position Sensor (TPS)

Self explanatory, it measures how far the accelerator petal is pushed. This tells the computer how aggressively the driver wishes to go, the computer is programmed to enrich fuel mixtures the further the throttle is opened. Just like an accelerator pump in a carburetor. Programming also alters the timing more aggressively to match. This sensor is very important in cluing the computer to future events, as it responds quicker to driver changes than any other sensor.

Vehicle Speed Sensor (VSS)

Self explanatory, it tells the computer how fast you are going. This allows certain emissions functions to be operated while on the highway. Also effects fuel delivery during deceleration.

Article & images courtesy of fordfuelinjection.com.

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