Saab 9000 - Page 77

74
Technical Description
Fault criteria, emission related misfire
Misfiring could be due to exhaust emissions excee-
ding permissible levels.
The number of misfires causing illegal exhaust emis-
sions depends to a certain extent on engine load and
speed.
An
engine load and speed dependent matrix in the
electronic control module's memory specifies how ma-
ny misfires per
1,000 engine revolutions are needed for
exhaust emissions to reach an illegal level.
1
2 1 2
2
When the condit1ons
·
for diagnosis are fulfilled, the
combustion signals from the ignition discharge mo-
dule are evaluated. The fault criteria are satisfied
when the number of misfires per 1000
engine revolu-
tions exceeds the matrix value.
Conditions for diagnosis
• Engine running
• Ignition timing synchronized
• No fuel shut-of
2 2
2
••••
Pin 17
34 34
34
34
34
34
Pin 18
Saab 9000