Circuit Description
The PCM times the intervals between each pulse of the crankshaft position
sensor and compares each time interval with the other 8 to determine when
an excessive change in crankshaft speed has occurred. This pulse is
generated from a 4X reluctor wheel located on the front of the crankshaft.
If the crankshaft speed is less than an expected amount, the PCM will
increase the amount of fuel needed to correct the misfire. If the amount
of fuel exceeds the calibrated value, the PCM will interpret this as
a misfire and set the DTC. The misfire diagnostic is used only to identify
a week cylinder needing additional fuel. This diagnostic will only
run once per ignition cycle.
Conditions for Running the DTC
The amount of fuel added to the cylinder is greater than the calibrated
value (internal to PCM).
Conditions for Setting the DTC
| • | Engine coolant temperature greater than 56°C (132°F). |
| • | Engine idling for a total of 90 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the
second consecutive drive trip the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic
fails. The first time the diagnostic fails, the Failure Records store this
information. If the diagnostic reports a failure on the second consecutive
drive trip, the Freeze Frame records the operating conditions at the
time of failure and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn off the MIL after three consecutive trips without
a fault condition |
| • | A History DTC will clear after 40 consecutive warm up if no failures
are reported by this or any other emissions related diagnostic. |
| • | The use of a scan tool. |
Diagnostic Aids
Important: Only diagnosis DTCs that display a status of Last Test Failed or Failed
This Igniton. Do not diagnosis any history DTCs. It's also possible multiple
History DTCs will set on a severe mechanical failure (total loss of compression).
It's possible adjacent misfire DTCs in the firing order may set (the
PCM will add fuel to the adjacent cylinders to improve idle quality). The
snap shot function on the scan tool can be used to determine exactly which
misfire DTC set first. A misfire DTC will only run once per igniton cycle
at idle. After 90 seconds of idle time has elapsed, and the misfire DTC
has passed, a misfire DTC will not set that ignition cycle. It maybe
necessary to perform multiple ignition cycles.
The most likely cause for this DTC is the following:
| • | A mechanical failure is causing low cylinder compression. |
| • | A fuel leak at the high pressure fuel injection lines or injection
nozzles. |
| • | A fuel injection nozzle is stuck closed. |
If an injection nozzle is suspected, it can be transferred to another
cylinder to determine if the DTC follows the nozzle.
After the repair has been performed, it may take approximately 30 seconds
for the vehicle to return to a stable idle.
