Low fuel pressure is a common reason for this code.
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CIRCUIT DESCRIPTION
The Crankshaft Position (CKP) sensor is the primary input to determine if misfire is occurring. Engine misfire is detected by monitoring crankshaft speed variations between cylinders. If a crankshaft deceleration occurs during a combustion or power stroke, the controls module (PCM/VCM) will compare this change in crankshaft speed to the previous cylinder. If the crankshaft speed change is more than a maximum allowable speed, the misfire is detected. Misfire may occur in a specific cylinder or all cylinders randomly.
When an engine is misfiring, brief decelerations in crankshaft rotational speed will be detected by the CKP. The controls module determines which cylinder has misfired based upon the Camshaft Position (CMP) sensor input. Misfire data is stored for each cylinder in separate accumulators. After 100 combustion events, the misfire totals are compared to a calibrated maximum number. If the misfire is excessive, this DTC will set.
CONDITIONS FOR RUNNING THE DTC
If start-up ECT temperature is below minus 7°C (20°F), misfire detection is delayed until ECT temperature is more than 21°C (70°F). If start-up ECT temperature is more than minus 7°C (20°F), misfire detection begins after a 5 second delay.
No active vehicle speed DTCs
No active TP sensor DTCs
No active MAF sensor DTCs
No active camshaft sensor DTCs
No active crankshaft sensor DTCs
The fuel level is more than 10 percent
The system voltage is between 11-16 volts
The engine speed is between 450-5000 RPM
The throttle position is steady within 2 percent for 100 ms
CONDITIONS FOR SETTING THE DTC
The VCM detects a deceleration in the crankshaft speed characteristic of either an emission type misfire or a catalyst damaging type misfire.
ACTION TAKEN WHEN THE DTC SETS
If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the MIL after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present.
CONDITIONS FOR CLEARING THE MIL/DTC
The control module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
A scan tool can clear the DTCs.
DIAGNOSTIC AIDS
The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring or use the history misfire counter for misfires that are not currently present. Many different conditions could cause an intermittent misfire.
Check for the following conditions:
Check the IC control circuit for an intermittent short to ground.
Check the spark plug wires and the coil wire for the following conditions:
- Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.
- Check the wire routing in order to ensure that crossfiring is not occurring.
- if the misfire occurs when the weather is damp, the problem could be due to worn plug wires.
Check for contaminated or a low fuel level and the following conditions:
- Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis. See: Computers and Control Systems > Component Tests and General Diagnostics
- If the fuel level is low, the fuel pump may draw air into the fuel rail, causing a stumble and possible misfire condition. Check the fuel trim numbers in the freeze frame to determine if this has occurred. It would be likely if the short term fuel number was above +20
- A restricted fuel filter can also cause a misfire.
Sticking intake or exhaust valves on engines with a misfire when cold.
Check HO2S for abnormal voltage readings. Check for a vacuum leak as a possible cause of the engine misfire.
An intermittent may be caused by any of the following conditions:
A poor connection
Rubbed through wire insulation
A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Diagrams.
TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
5. The misfire is considered random on all cylinders if, while viewing the misfire fire counters in the misfire data list, the misfire seems to move to different cylinders.
6. The misfire is considered consistent if the misfire is occurring on the same cylinder(s) consistently.
7. When checking the spark at the spark plug wires, the spark should be consistent. A few sparks then nothing is no spark.
Thursday, November 1st, 2018 AT 12:56 AM
