ADC: Analog to Digital Converter

A/D: Analog to Digital

AFR : Air Fuel Ratio (sometimes written as A/F) - ideal ratio of 14.7:1 gives low emissions and acceptable drivability and economy. A lower ratio (11:1) would be "rich" and a higher ratio (16:1) "lean".

ALDL : Assembly Line Diagnostic Link - The connector under the dash on GM cars. It can be used to dump diagnostic information from the ECM, but requires special equipment to use.

BDC : Bottom Dead Center

BLM : Block Learn Multiplier - the factor which is "learned" to adjust fuel mixture. See Thrasher's "gem" mentioned on the main page here.

BP : Barometric Pressure

BPW : Base Pulse Width - the calculated length of the pulse, or "on-time" of the fuel injector before any "tweaking" for minor inputs such as air temperature.

C3I (aka DIS) : Computer Controlled Coil Ignition system.

CAN : Controller Area Network. A proposed network protocol for automotive use outside the US. The US proposal is SAE standard J1859, aka OBD.

CDI : Capacitive Discharge Ignition. See myfaq.

CE : Check Engine - dashboard light (same as SES) letting you know the car has a problem and also used to flash out diagnostic codes stored by the ECM.

CFI : Crossfire Fuel Injection - an intake manifold utilizing 2 diagonally mounted throttle bodies (model 300s?), hence it's another TBI injection system. The twin 300s together are called the model 400.

CFI : Central Fuel Injection - a FoMoCo designation. Similar to GM's TBI injection system.

CFI : Continuous mechanical Fuel Injection - yet another injection system. This one used on Volvos.

Crossings : the number of times the O2 sensor switches across stoich. It is a measure of closed loop system performance.

CTS : Coolant Temp Sensor

CYA : Cover Your A**

DAC : Digital to Analog Converter

DERM : Diagnostic Energy Reserve Module. Airbag box, separate from PCM. Stores codes, crash event data, retains power to ignite air bag when battery power is lost (ref Shannen Durphey -- DIY_EFI email on 14 Jun 1998).

DIS (aka C3I) : Distributorless Ignition System

EEC : Evaporative Emission Control system - a method of purging fuel vapors (don't tell the Ford faithful whose EFI controller is known as the EEC-IV or EEC-V)

ECM : Electronic Control Module (other manufacturers call this an ECU or Electronic Control Unit) - the engine management computer.

EGO : Exhaust Gas Oxygen sensor

EGR : Exhaust Gas Recirculation - use to reduce emissions and increase economy supposedly

EGT : Exhaust Gas Temperature

EPROM : Electrically Programmable Read-Only Memory - this is the replaceable memory chip which contains fuel and spark information and allows one ECM to be used in various applications.

ESC : Electronic Spark Control - aka Retard Signal. Used to retard the timing when detonation (knock) is detected.

EST : Electronic Spark Timing

FUBAR : F***ed Up Beyond All Recognition

HEI : High Energy Ignition

IAC : Idle Air Control - (a controlled vacuum leak) A stepper motor controlled by the ECM. It determines how much air gets through to the engine when the throttle is at idle. The ECM controls it to maintain a programmed idle speed.

IAT : Intake Air Temperature. Similar (equivalent?) to MAT.

ION :  A patented (by Saab) method for detecting "knock" or misfire in an engine by measuring a current across the sparkplug electrode known as an ionization current. See ION.

ISCV : Idle Speed Control Valve

MAF : Mass Air Flow (sensor) - an alternative to MAP. This measures actual airflow into the engine and thus doesn't need to make any calculations based on VE.

MAP : Manifold Air Pressure (sensor) - a vacuum gauge. BPW fueling is primarily computed from this input on cars so equipped. Another alternative would be MAF.

MAT : Manifold Air Temperature - if it's different from IAT I don't know how. The '7747 doesn't use either. :)

MCU : MicroController Unit (eg. 68HC11) - the processor on which the computer is based

MPFI: Multi-Port Fuel Injection (see MPI)

MPI : Multi-Port Injection - generic name for any of the port injection systems (as opposed to TBI systems)

O2 (see also EGO) : Typical slang referring to the Oxygen sensor

OBD = On Board Diagnostics. Mandated in the US, this forces auto manufacturers to use common protocols and connectors for automotive diagnostics.

OEM : Original Equipment Manufacturer

PLCC : Plastic Leadless Chip Carrier

PPM : Pulse Per Mile - in reference to VSS

PWM : Pulse Width Modulator

RPM : Revolutions Per Minute - typically sensed by a sensor in the distributor or on the crankshaft.

SAE : Society of Automotive Engineers

SBC : Single Board Computer or Small Block Chevy

Scantool : A piece of test equipment which plugs into the ALDL and displays Trouble Codes and other information helpful for servicing of the ECM.

SD : Speed density. An FI technique where the amount of air entering the engine is calculated from engine RPM, MAP, and a pre-calculated volumetric efficiency for the engine.

SES : Service Engine Soon light - aka "Check Engine" light

SFI : Sequential Fuel Injection - injectors are fired in ignition firing order for maximum performance and economy.

SNAFU : Situation Normal..all f***ed up.

SOL : Sh** Outta Luck

TBI : Throttle Body Injection - basically a fully electronic computer controlled carburetor

TCC : Torque Converter Clutch - a lockup mechanism for improved economy and performance

TDC : Top Dead Center. Piston at the top of the cylinder.

TPI : Tuned Port Injection - intake manifold and EFI system used on Camaros and Corvettes especially

TPS : Throttle Position Sensor. Tells the ECM how "open" the throttle is.

VE : Volumetric Efficiency - the ratio of the amount of air going into an engine to the volume displaced by the movement of the pistons

VIN : Vehicle Identification Number - needed when using the scantool

VSS : Vehicle Speed Sensor - one type is the 2000ppm unit.

Hex Table

VIN Codes

Motorola or S19 format

Electronics Notations

Resistor Color Codes