ECM (Engine Control Module)
The computer brain that controls various aspects of your motorcycle's performance including ignition, timimg, and fuel to air ratio.

ECU (Engine Control Unit)
In electronic injection engines, the central processing unit supervises ignition and injector management.

Engine-control system
A computerized brain that regulates an engine's operation by monitoring certain engine characteristics (rpm, coolant temperature, intake airflow, etc.) through a network of sensors and then controlling key variables (fuel metering, spark timing, EGR, etc.) according to pre-programmed schedules.

EFI
(EFI) is a fuel delivery mechanism that eliminates the need for a carburetor. A computerized control system accounts for elevation changes and delivers the necessary information to the EFI system to change the air-to-fuel mixture to achieve optimal fuel economy and engine performance.

Exhaust-gas Recirculation (EGR)
A method of reducing NOx (oxides of nitrogen) exhaust emissions by recirculating some of the engine's exhaust gas into the intake manifold. The exhaust gas serves as inert filler that absorbs heat during the combustion process and reduces the peak temperature reached during combustion.

ELECTRIC FUEL PUMP
The electric fuel pump is a roller-cell pump driven by a permanent-magnet electric motor.

ELECTRONIC INJECTION
Assembly of electromechanical and electronic devices for the preparation and injection in the inlet tracts of the most suitable air-fuel mixture for each engine operation condition.

ENGINE KNOCK
Engine “knock” is the sound produced when a car’s air/fuel mixture is ignited by something other than the spark plug, such as a hot spot in the combustion chamber. Light knock is normal in modern engines during heavy acceleration or under other high-load conditions, such as climbing steep grades. Severe “knock” may be caused by fuel with too low an octane rating or by improper adjustment of the ignition system. This will harm the engine. “Knock” is also called “detonation” or “ping.”

ENGINE MANAGEMENT
The engine-mangement system's first and foremost task is to regulate the engine's torque generation by controlling all of thos functions and factors in the various engine-management subsystems that determine how much torque is generated.

Engine Types
F-Head Side exhaust valve and overhead inlet valve.
L-Head Both valves on one side of the cylinder.
T-Head Exhaust valve on one side and inlet valve on the other side of the cylinder. (Twin-camshafts).
I-Head Both valves located directly over the piston. Also called valve--in-head or overhead valve engine. SOHC Single overhead camshaft.
DOHC Double overhead camshafts.

ENGINE VACUUM
Is the air signal created by the intake stroke, pulling in the air/fuel mixture.

ENRICHENER
A device that restricts the air intake to result in a richer fuel mixture which assists in starting the engine. This is a term used by Harley-Davidson. Another, more commonly used, term is Choke. Most motorcycles have knobs or levers to pull out to decrease the air intake. After the engine has warmed up, the enrichener may be pushed back in.

EVOLUTION (EVO)
The name of the Harley-Davidson engine used from 1984-1999, sometimes called the EVO. The engine is a 45 degree V-Twin displacing 80ci/1340cc.

EXHAUST-GAS ANALYZERS
Legislation reflects govermental efforts to reduce the quanities of toxic substances in exhaust gases by mandatting regular periodic emissions testing fo vehicles already in service.

Exhaust Manifold
The network of passages that gathers the exhaust gases from the various exhaust ports and routes them toward the catalysts and mufflers of the exhaust system. A manifold with free-flowing passages of a carefully designed configuration, called a "header," can improve breathing.

Exhaust Port
The passageway in the cylinder head leading from the exhaust valves to the exhaust manifold.