Exhaust Gas Recirculation (Egr) System Check - Isuzu 1999 RODEO Workshop Manual

6E1–98
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

EXHAUST GAS RECIRCULATION (EGR) SYSTEM CHECK

Circuit Description
A properly operating exhaust gas recirculation (EGR)
system will directly affect the air/fuel requirements of the
engine. Since the exhaust gas introduced into the air/fuel
mixture is an inert gas (contains very little or no oxygen),
less fuel is required to maintain a correct air/fuel ratio.
Introducing exhaust gas into the combustion chamber
lowers combustion temperatures and reduces the
formation of oxides of nitrogen (NOx) in the exhaust gas.
Lower combustion temperatures also prevent detonation.
If the EGR pintle were to stay closed, the inert exhaust
gas would be replaced with air and the air/fuel mixture
would be leaner. The powertrain control module (PCM)
would compensate for the lean condition by adding fuel,
resulting in higher long term fuel trim values.
Diagnostic Aids
The EGR valve chart is a check of the EGR system. An
EGR pintle constantly in the closed position could cause
detonation and high emissions of NOx. It could also result
in high long term fuel trim values in the open throttle cell,
but not in the closed throttle cell. An EGR pintle constantly
in the open position would cause rough idle. Also, an EGR
valve mounted incorrectly (rotated 180°) could cause a
rough idle without setting an EGR DTC. Check for the
following items:
f EGR passages – Check for restricted or blocked EGR
passages.
f Manifold absolute pressure sensor – A manifold
absolute pressure sensor may shift in calibration
enough to affect fuel delivery. Refer to Manifold
Absolute Pressure Output Check.
D06RX055