DTC P0300 Engine Misfire Detected. Oldsmobile Shelby Series 1 1999

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1999 🢒 Shelby Series 1 🢒 Engine 🢒 Engine Controls - 4.0L 🢒 DTC P0300 Engine Misfire Detected

Circuit Description

The crankshaft position (CKP) sensors are mounted through the left side of the engine block. The CKP sensors work in conjunction with a 24X reluctor wheel on the crankshaft.

A misfire causes a change in crankshaft speed. The powertrain control module (PCM) times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in crankshaft speed has occurred. You can expect a certain amount of acceleration or deceleration between each firing stroke, but if the crankshaft speed changes are more than an expected amount, the PCM interprets this as a misfire.

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0500, and ignition control (IC) DTCs are not set.

•	The engine speed is between 800 RPM and 3,600 RPM.

•	The ignition voltage is between 11.0 volts and 16.0 volts.

•	The engine coolant temperature is between -7°C (19°F) and +115°C (239°F).

•	Fuel level more than 10 percent

•	Rough road indication is not considered present.

•	The throttle position (TP) sensor angle is steady within 3 percent.

•	The transmission is not changing gears.

•	The A/C clutch is not changing states.

•	The PCM is not in fuel shut-off or decel fuel cut-off mode.

Conditions for Setting the DTC

•	The PCM determines that an emission type Misfire is present.

•	The PCM determines that a catalyst damaging Misfire is present.

Action Taken When the DTC Sets

The PCM illuminates the malfunction indicator lamp (MIL) under the following conditions:

•	The PCM illuminates the MIL on the second consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions, such as load, RPM, temperature, as the previous ignition cycle that the test ran and failed.

•	The first time the diagnostic fails, the PCM records the operating conditions in Failure Records.

•

The PCM determines the percent of misfire over a 1,000 revolution period is high enough to cause excessive tail pipe emissions. The PCM illuminates the MIL the next consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions, such as load, RPM, temperature, as the previous ignition cycle that the test ran and failed.

•	The PCM flashes the MIL when the diagnostic runs and fails a catalyst damaging misfire.

Conditions for Clearing the MIL/DTC

Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than the three ignition cycles. Review the Freeze Frame and Failure Records for the last failure conditions.

•	The PCM turns the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail within the same conditions that the DTC last failed.

•	A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.

•	A last test failed, or current DTC, clears when the diagnostic runs and does not fail.

•	Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important:

•	Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/ or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.

•	For any test that requires probing the PCM or component harness connectors, use the J 35616 connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Wiring Systems for procedures.

•	Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have DTC P0461 also set.

•	A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis .

•	A misfire may not be apparent at idle. The misfire may only occur above idle under a load. Road test the vehicle and monitor the misfire current counters.

•	Observe if more then one cylinder is mis-firing, the scan tool may only display one cylinder mis-firing. This will not be apparent until the repair is completed.

•	Excessive vibration from sources other than the engine could cause a misfire DTC. The following are possible sources of vibration:

-	Variable thickness brake rotor

-	Drive shaft not balanced

-	Certain rough road conditions

•	For an intermittent condition, refer to Symptoms .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

A misfire may not be apparent at idle. The misfire may only occur above idle or under a load. Road test the vehicle and monitor the misfire current counters.

The Misfire current counters will not increment if certain DTCs set at the same time or after DTC P0300 sets. Refer to the Conditions for Running in DTC P0300 for applicable DTC list.

If more than one cylinder is misfiring, the Misfire current counters may increment for only one cylinder.

If one injector fuse open, only two or three Misfire current counters may increment for the corresponding side of the engine.

Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.

If a misfire is present and you suspect a fuel control condition, force the fuel system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.

The cylinder with the more significant misfire may cause another cylinders counter to increment only by a small amount.

If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.

If you cannot locate a fuel system condition, refer to Engine Mechanical. An engine mechanical condition can cause a spark plug to gas foul. Inspect for collapsed lifters or worn camshaft lobes.

If the customers concern is the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.

DTC P0300 - Engine Misfire Detected

Step

Action

Values

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Important:

•	You must perform the CKP System Variation Learn Procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .

•	If any DTCs are set, refer to those DTCs before proceeding with this diagnostic.

Monitor all the Misfire Current counters on the misfire data list using the scan tool. There are a total of 8 counters. One counter per cylinder.

Are any of the Misfire Current counters incrementing?

Go to Step 4

Go to Step 3

Turn ON the ignition leaving the engine OFF.
Review the Freeze Frame and/or Failure Records data for this DTC and observe the parameters.
Turn OFF the ignition for 15 seconds.
Start the engine.
Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in Freeze Frame and Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
Select the Diagnostic Trouble Code (DTC) option.

Does the scan tool indicate that this diagnostic failed this ignition?

Go to Step 4

Go to Diagnostic Aids

Is only one Misfire counter incrementing?

Go to Step 6

Go to Step 5

Visually and physically inspect the following items:

•	Vacuum hoses for splits, kinks and proper connections -- Refer to Emission Hose Routing Diagram .

•	Throttle body and intake manifold for vacuum leaks

•	Crankcase ventilation valve and system for vacuum leaks -- Refer to Crankcase Ventilation System Description .

•	PCM grounds for being clean and secure --Refer to Ground Distribution Schematics in Engine Electrical.

•	Verify that all injector harness connectors are connected to the proper injector or cylinder.

•	Inspect the injector and ignition control fuses for being open. If you find an open fuse, locate and repair the shorted circuit. Refer to Wiring Repairs in Wiring Systems.

•	Test for low fuel pressure or restricted fuel flow. Refer to Fuel System Diagnosis .

•	Inspect for a restricted exhaust. Refer to Restricted Exhaust System Check .

•	Fuel contamination -- Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

If you find a condition, repair as necessary.

Did any of the above tests isolate a condition requiring a repair?

Go to Step 17

Go to Step 6

Turn OFF the ignition.
Disconnect the injector that corresponds to the Misfire Cur counters that were incrementing.
Connect the J 34730-2C injector test lamp to the injector electrical connector.
Idle the engine.

Is the injector test lamp flashing?

Go to Step 7

Go to DTC P0200 Injector Control Circuit

Turn OFF the ignition.
Reconnect the injector harness electrical connector.
Disconnect the ignition wires from the spark plug that corresponds to the Misfire Cur counters that were incrementing.
Install a J 26792 spark tester to ground.
Ground the companion cylinders plug wire.
Start the engine.

Does the spark jump the tester gap and is the spark consistent?

Go to Step 9

Go to Step 8

Remove the ignition wire for the cylinder that is misfiring.
Measure the resistance of the ignition wire using the DMM.

Is the ignition wire resistance less than the specified resistance?

700 ohms

Go to Electronic Ignition (EI) System Diagnosis

Go to Step 16

Remove the spark plugs from the cylinder that indicated a misfire.
Visually inspect the spark plugs.

Does the spark plug appear to be OK?

Go to Step 10

Go to Step 11

Important: If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Swap the suspected spark plug with another cylinder that is operating properly.
Operate the vehicle under the same conditions that the misfire occurred.

Did the misfire move with the spark plug?

Go to Step 15

Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F)

Are the spark plugs oil or coolant fouled.

Go to Base Engine Misfire Diagnosis in Engine Mechanical

Go to Step 12

Important: If the fuel system is OK, refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Are the spark plugs gas fouled?

Go to Fuel System Diagnosis

Go to Step 13

Important: If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Do the spark plugs show any signs of being cracked, worn, or improperly gapped?

Go to Step 14

Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F)

Replace or re-gap spark plugs. If improper gap is found, be sure to re-gap spark plugs using a wire type gauge.

Is the action complete?

Go to Step 17

Replace the faulty spark plugs.

Is the action complete?

Go to Step 17

Replace the faulty ignition wires.

Is the action complete?

Go to Step 17

Was the customers concern that the MIL was flashing?

Go to DTC P0420 Catalyst System Low Efficiency Bank 1 or DTC P0430 Catalyst System Low Efficiency Bank 2

Go to Step 18

Select the DTC option and the Clear DTC Information option using the scan tool.
Idle the engine at the normal operating temperature.
Select the DTC option.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

Go to Step 19

Go to Step 2

Select the Capture Info option and the Review Info option using the scan tool.

Does the scan tool display any DTCs that you have not diagnosed?

Go to the applicable DTC table

System OK