C 3500 Truck 2WD V8-454 7.4L VIN J SFI (1999)
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Silica
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Lead
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Phosphorus
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Exhaust system leaks may cause the following:
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Prevent a degraded or marginal TWC converter from failing a diagnostic test.
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Cause a normally functioning TWC converter to fail a diagnostic test.
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Prevent the diagnostic test from running.
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An aftermarket HO2S.
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An aftermarket catalytic converter.
Misfire Monitor Diagnostic Tests
When the engine is running and a cylinder misfires the crankshaft slows down momentarily. The control module has the ability to detect this change in
speed by monitoring the input signals from the following sensors:
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The crankshaft position (CKP) sensor
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The camshaft position (CMP) sensor.
When the control module is running the misfire on-board diagnostic tests and a misfire is detected the misfire counter stores (accumulates) the position
and the number of misfires. Two counters (accumulators) are assigned to each of the cylinders. The counters are as follows:
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The Current Misfire Counters. The current misfire counters store the number misfires that have occurred in the last 200 engine cycles. When the
control module detects an unacceptable amount of misfires stored in a current misfire counter the misfire on-board diagnostic test fails and a
misfire DTC will set.
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The History Misfire Counters. When a misfire DTC is set, the history misfire counters store the total number of misfires that have occurred every
200 engine cycles.
Misfire Counters
Throttle Position Sensor Connector
The Misfire Counters graphic illustrates how the misfire diagnosis and the diagnostic executive use the misfire counters (accumulators). When a misfire
diagnostic test fails and reports to the diagnostic executive that a misfire condition exist, the diagnostic executive reviews all of the misfire counters in
order to store the most current misfire information.
