P0304 Cylinder 4 misfire, haven't been able to pinpoint what it is.
Pontiac Sunfire GT 2.. I cleaned the TB along with everything in there. I have tried different coil pack housing, I have ACDelco Plugs only thing I haven't looked at is the fuel system. Where should I start there?
1
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
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Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check
2
Turn ON the ignition switch leaving the engine OFF.
Install a scan tool.
Was a DTC P0200 set?
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Go to DTC P0200 Injector Control Circuit
Go to Step 3
3
Turn OFF the ignition switch.
Perform a visual/physical inspection. Refer to the Symptoms for the visual/physical inspection procedure.
Make any necessary repairs.
Were any repairs necessary?
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Go to Step 25
Go to Step 4
4
Start the engine.
Idle the engine.
Observe the Misfire Current Counters with the scan tool.
Is the Misfire Current #1 counter incrementing?
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Go to Step 5
Go to Step 6
5
Turn OFF the ignition switch.
Remove the air cleaner outlet resonator assembly. Refer to the Air Cleaner Outlet Resonator Replacement for the removal procedure.
Disconnect all the fuel injector electrical connectors.
Disconnect the ICM 11 pin electrical connector.
Temporarily remove the ignition coil and the electronic Ignition Control Module (ICM) assembly.
Reconnect the ICM 11 pin electrical connector.
Install the J 36012-A spark plug jumper wires into the spark plug boot assemblies.
Install the J 26792 spark plug tester on the spark plug jumper wire for cylinder #4.
Remove the spark plug boot assembly from cylinder # 1 of the ignition coil housing.
Install a jumper wire from the #1 spark plug connector of the ignition coil housing to ground.
Connect a jumper wire to the ICM assembly to ground.
Crank the engine with the remaining spark plugs wires still connected.
Does the spark tester spark?
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Go to Step 7
Go to Step 10
6
Turn OFF the engine leaving the ignition switch ON.
Review the Freeze Frame data and record the parameters.
Start the engine.
Operate the vehicle within the Freeze Frame conditions and Conditions For Running the DTC as specified.
Observe the Misfire Current Counters with the scan tool.
Is the Misfire Current #1 counter incrementing?
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Go to Step 5
Go to Step 25
7
Turn OFF the ignition switch.
Remove the spark plug from cylinder #4.
Exchange the spark plug with a spark plug from a known good cylinder.
Reconnect all the fuel injector electrical connectors.
Install the spark plug boot assembly to the #1 spark plug connection at the ignition coil housing.
Reconnect the spark plug jumper wire to the spark plug boot assembly.
Start the engine.
Run the vehicle when the misfire was present.
Is the Misfire Current #4 counter incrementing?
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Go to Step 8
Go to Step 9
8
Check for a leaking fuel injector. Refer to DTC P0200 Injector Control Circuit starting at step 5.
If the fuel injector is OK, check for a basic engine problem. Refer to Base Engine Misfire Diagnosis in Engine Mechanical.
Is the action complete?
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Go to Step 25
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9
Turn OFF the ignition switch.
Replace the spark plug. Refer to the Spark Plug Replacement in Engine Electrical.
Is the action complete?
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Go to Step 25
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10
Turn OFF the ignition switch.
Remove the spark plug boot assemblies from the affected coil.
Disconnect the ICM 11 pin electrical connector.
Connect a DMM between the secondary ignition coil terminals at the ignition coil housing.
Is the resistance between the specified value?
4-8Kohms
Go to Step 11
Go to Step 12
11
Remove the coil housing. Refer to the Ignition Coil(s) Replacement for the coil housing removal procedure.
Disconnect the coil harness electrical connector from the ICM.
Reconnect the ICM 11 pin electrical connector.
Connect a test light to B+.
Probe the #1 and #4 coil control terminal C with the test light.
Crank the engine while watching the test light.
Does the test light blink?
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Go to Step 13
Go to Step 14
12
Remove the #1-#4 ignition coil from the ignition coil housing. Refer to the Ignition Coil(s) Replacement for the coil removal procedure.
Recheck the resistance between the secondary terminals of the #1-#4 ignition coil.
Is the resistance between the specified value?
4-8Kohms
Go to Step 15
Go to Step 16
13
Remove the ignition coils from the ignition coil housing.
Disconnect the ignition coil electrical connector from the ignition coils.
Reconnect the ignition coil electrical connector to the ICM.
Connect a test light to ground.
Important
Carefully handle the ignition coils electrical connectors to avoid spark arching from the electrical terminals and causing the fuse to open which would leading to misdiagnosis.
Turn ON the ignition switch leaving the engine OFF.
Probe the ignition feed circuit to the ignition coils at both of the ignition coil electrical connector terminals B with the test light.
Does the test light illuminate for both circuits?
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Go to Step 19
Go to Step 20
14
Turn OFF the ignition switch.
Disconnect the ICM 11 pin electrical connector.
Visually inspect the ICM 11 pin electrical connector to see if the electrical connections are clean and tight. Refer to the Symptoms for the visual/physical inspection procedure.
Make any necessary repairs. Refer to Wiring Repairs in Wiring Systems.
Were any repairs necessary?
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Go to Step 25
Go to Step 17
15
Check and replace the following item(s) as necessary:
Ignition coil spring for cylinders #1 and #4 coils
Ignition coil housing
Is the action complete?
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Go to Step 25
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16
Replace cylinders #1 and #4 ignition coil. Refer to the Ignition Coil(s) Replacement .
Is the action complete?
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Go to Step 25
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17
Reconnect the ICM 11 pin electrical connector.
Disconnect the PCM electrical connector (C1).
Reconnect the #4 spark plug boot assembly to the #4 spark plug connector at the ignition coil housing.
Reconnect the spark plug jumper wire to the #4 spark plug boot assembly.
Reconnect the J 26792 spark tester on the #4 spark plug wire.
Connect a jumper wire to the #1 spark plug connector at the ignition coil housing to ground.
Turn ON the ignition switch leaving the engine OFF.
Connect a test light to B+.
Notice
Do not leave the test lamp connected to the PCM IC circuit connector for longer than 5 seconds at a time. Failure to do so may damage the ignition coil and/or the Ignition Control Module.
Momentarily touch the IC input circuit at the PCM electrical connector (C1-26). A spark should be present when the test light is removed from the IC input circuit.
Is there a spark present when you remove the test light from the IC input circuit?
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Go to Step 23
Go to Step 18
18
Turn OFF the ignition switch.
Check for the following conditions in the ignition control input circuit.
Open circuit
Short to ground
Short to B+
Poor electrical connection at the ICM
Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.
Were any repairs necessary?
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Go to Step 25
Go to Step 22
19
Check the #1-4 coil control circuit for the following conditions:
Poor electrical connection to the ICM and ignition coil
Open circuit
Short to ground
Short to voltage
Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a repair necessary?
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Go to Step 25
Go to Step 21
20
Turn OFF the ignition switch.
Repair the open in the ignition feed circuit between the #1-4 and #2-3 ignition coils electrical connectors. Refer to Wiring Repairs in Wiring Systems.
Is the action complete?
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Go to Step 25
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21
Turn OFF the ignition switch.
Check the ignition feed circuit for a poor electrical connection at the ignition #1 -#4 coil.
If the electrical connection is OK, replace the spark plug boot assembly.
Is the action complete?
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Go to Step 25
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22
Turn OFF the ignition switch.
Replace the ICM. Refer to the Ignition Control Module Replacement .
Is the action complete?
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Go to Step 25
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23
Turn OFF the ignition switch.
Inspect the PCM electrical connector and connections.
Repair the electrical connector and the connections as necessary. Refer to Wiring Repairs in Wiring Systems.
Were any repairs necessary?
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Go to Step 25
Go to Step 24
24
Replace the PCM. Refer to the PCM Replacement .
Is the action complete?
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Go to Step 25
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25
Reconnect all previously disconnected components (if not already reconnected).
Connect all the fuel injector electrical connectors.
Install the air cleaner outlet resonator assembly. Refer to the Air Cleaner Outlet Resonator Replacement for the installation procedure.
Clear the DTCs with the scan tool.
Start the engine.
Idle the engine at the normal operating temperature.
Operate the vehicle within the conditions for running this DTC and P0420 as specified in the supporting text.
Does the scan tool indicate that these diagnostics have ran and passed?
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Go to Step 26
Go to Step 2
26
Check to see if any additional DTCs are set.
Does the scan tool display any DTCs that you have not diagnosed?
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Go to applicable DTC table
System OK
