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72
Technical Description
Fault criteria, catalyst damaging misfire
Misfiring could be due to the fuel-air mixture that
should have been burnt in the engine being burnt in
the three way catalytic converter instead.
The number of misfires that cause an overheated
and consequently damaged three way catalytic con-
verter depends on engine load and speed.
An· engine load and speed dependent matrix in the
electronic control module's memory specifies how
many misfires per 200 engine revolutions will dama-
ge the three way catalytic converter.
1
2
34
34
34 34
When the conditions 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 200 engine revolu-
tions exceeds the matrix valt..ie.
Conditions for diagnosis
• Engine running
• Ignition timing synchronized
• No fuel shut-of
2 2
2
Pin 17
34
34
Pin 18
Saab
9000
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