Workshop Manual

6E–266
6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0304 Cylinder Misfire Detected
Circuit Description
Misfire is monitored as a function of the combustion
quality (CQ) signals generated from the ignition current
sense system. Combustion signals represent the degree
of combustion in each cylinder. Misfire is detected when
the combustion signal is below a predetermined value.
This DTC P0304 will determine if the No.4 cylinder misfire
is occurring by monitoring the Combustion Quality.
Conditions for Setting the DTC
B None of the following DTCs occur: TP sensor, MAF
sensor, vehicle speed sensor, ECT sensor.
B The engine speed is between 600 and 6250 RPM.
B The system voltage is between 11 and 16 volts.
B The ECT indicates an engine temperature between
–7°C (28°F) and 110°C (230°F).
B The throttle angle is steady and throttle change less
than 2% per 125 milliseconds.
Action Taken When the DTC Sets
B The PCM will ON the MIL after second trip with
detected the fault.
B If the misfire is severe enough to cause possible
catalyst damage, the PCM will flash the MIL for as long
as the misfire remains at catalyst damaging levels.
B The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC
B The PCM will turn the MIL “OFF” on the third
consecutive ignition cycle in which the diagnostic has
been run and the fault condition is no longer present.
B A history DTC P0304 will clear after 40 consecutive
ignition cycles occur without a fault.
B DTC P0304 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:
B System grounds – Ensure all connections are clean
and properly tightened.
B Injector – Perform the injector coil/balance test to
locate a faulty injector that contributes to a lean
condition on the affected cylinder. In addition to the
above test, check the condition of the injector O-ring.
B Faulty spark plug – Check for a cracked insulator,
carbon tracking, incorrect gap, and worn electrodes.
B Damaged or faulty ignition coil – Check for cracks,
carbon tracking or other damage.
B Substitute a known good coil – Swap the ignition coils
and retest. If the misfire follows the coil, replace the
ignition coil.
DTC P0304 – Cylinder Misfire Detected
Step Action Value(s) Yes No
1 Was the “On-Board Diagnostic (OBD) System Check”
performed?
— Go to Step 2
Go to OBD
System
Check
2 1. Start the engine. Run the engine at idle.
2. Review and record Tech 2 Freeze Frame data.
3. Monitor “Misfire Cur. #4” on the Tech 2.
Is “Misfire Cur. #4” increasing (indicating a misfire
currently occurring)?
— Go to Step 4 Go to Step 3
3 Monitor “Misfire Hist. #4” while operating the vehicle to
duplicate the conditions present when the DTC was set
(as defined by the Freeze Frame data recorded in Step
2).
Is “Misfire Hist. #4” increasing (indicating a misfire
currently occurring)? — Go to Step 4
Refer to
Diagnostic
Aids
4 1. Visually and physically inspect the vacuum hoses
for splits, kinks, and improper connections. Also,
inspect the intake manifold for a vacuum leak.
2. If a problem is found, repair it as necessary.
Did the inspection reveal a problem?
— Verify repair Go to Step 5
5 1. Install a spark tester at the spark plug end of the
cylinder #4 ignition wire.
2. Crank the engine while observing the spark tester.
A crisp, blue spark should be observed.
Is adequate spark present?
— Go to Step 8 Go to Step 6