EFIS or Electronic Fuel Injection Simplified

This is a tour of a typical automotive EFI System. This will start with the various input sensors and the functions that they perform. We will then cover what the Electronic Control Unit (ECU) does and what are its signals. I have included a wiring guide for each of the seniors and the ECU.

SENSORS

TPS(Throttle Position Sensor)

The TPS provides a signal that changes relative to the throttle butterfly posion. It is located on the throttle body on the butterfly shaft. Use a voltmeter to verify it's operation.
TPS signal voltage will vary from 1.25vdc to 5.0vdc (wide open)
Connection Color ECU
TPS +5v blue/orange C14
TPS GND black D2
TPS signal yellow/blue C13
Oxygen Sensor

The Oxygen sensor is a thermocouple, that generates a DC voltage proportional to the temperature of the exhaust gas. It is located on the exhaust manifold near the engine exhaust ports. It's normal operation temperature is 600 deg F.
The Oxygen sensor's output will vary between 0.1vdc (lean) to 1.0vdc (rich).
Connection Color ECU
O2 blue D7
O2 Gray/Black D6
CTS  (Coolant Temperature Sensor)

The CTS uses a thermistor to vary a signal voltage to the ECU. It is usually found by a water manifold.
It's output is about 1.5vdc to 2.0vdc
Connection Color ECU
CTS + Gray/Black C10
CTS - Gray/Black C11
IATS  (Intake Air Temperature Sensor)

The IATS uses a thermistor to vary a signal voltage to the ECU. The ECU applies a 4 to 6vdc to the sensor.
When the intake air is cold the resistance is high.


Connection Color ECU
IATS + Blue/Black C12
IATS - Blue/Black D2
MAP Sensor(Manifold Absolute Pressure)

The MAP Sensor responds to changes in manifold pressure. This signal also changes in altitude. The MAP input to the ECU adjusts the fuel/air ratio. ( It's a small black box on the passenger side of the firewall on our Ford Taurus.)


Connection Color ECU
MAP signal Gray/Red C11
MAP - Gray A11
MAP + Blue/Orange C14
CPR Sensor(Crank Pulse Reference)

This signal is used in engine timing and determines TDC (Top Dead Center).


Connection Color ECU
CPR Yellow/Red B5

Output Devices

Fuel Injectors

This device is a solenoid that opens and closes at a rate, dependent on throttle position, and other inputs to the ECU. Fuel pressure is typically 36psi.

Connection Color ECU
FI Blue/White D15
FI Blue/Yellow C15
Intake Air Control Valve

The IACV allows air to be fed into the intake manifold to maintain an idle.

Connection Color ECU

ECU

The ECU is nothing more than a small computer with its program in ROM, or Read Only Memory. Performance PROMs are available in the automotive hot rod marketplace, but their advantages to aircraft auto conversions remain unproven. The ECU can be reset by removing all power to it. This causes the ECU to clear it's RAM, or Random Access Memory, and to use it's factory defaults.

On start up the ECU checks the temperature with the CTS or Coolant Temperature Sensor. When the engine block is cold, the ECU  increases the fuel flow to richen the mixture. As the engine warms up, the ECU will lean out the mixture. The ECU also monitors the TPS, Oxygen, and MAP sensors to produce the most power, while using the least amount of fuel.


It is mandatory to refer to the specific MAKE, MODEL and YEAR  shop manual or wiring guide for  numbering and color coded connections! ! The guides in your local parts stores are NOT good. Please go to you local dealer and order the specific manual or wiring guide.   The  $15 or $20 that you spend will save you $200 or more if you blow up your computer!!


The original author is Steve Parkman (Contact! San Deago EZ Flyer newsletter)

I have extensively edited this note... Thanks C A Harrison 15Jul1999