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FYI
- EGR
Submitted
by Bluegrass / 12-17-06
What is it? Exhaust Gas Recirculation.
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Why?
It's used to reduce combustion temperatures during cruise where
the engine spends most of it's time running. This has the effect of
reducing emissions of nitrogen oxide into the atmosphere; a federal
regulation.
How?
The computer (EEC) keeps track of where the throttle position is,
how long in that relative position and the speed of the car. These conditions
infer a 'cruise condition' is taking place at light throttle and loading.
What happens?
The computer powers a vacuum control valve called the EVR. This
gates vacuum to the EGR valve diaphragm causing it to open allowing
exhaust gas to flow into the intake manifold. During this time, the
ignition timing is advanced and the fuel is cut to a low value. This
action improves fuel mileage as well as reduces combustion temperatures.
When does this operation take place?
Never at idle or beyond 7/8 throttle. This action has little effect
on engine power except what heat it may add to the air intake temperature.
How does the computer know this action works?
On top of the EGR valve there is a sensor called the EVP. This device
reports its operation back to the computer as a result of the internal
movement of the EGR.
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