PACCAR MX (2004 Emissions) Fault Code: P0304 Cylinder 4 – Contribution Too Low or Misfire

PACCAR MX (2004 Emissions) Fault Code: P0304 Cylinder 4 – Contribution Too Low or Misfire

SET CONDITIONS:
The PCI ECU (D420) detects that cylinder 4 is misfiring or the combustion contribution is lower relative to the other cylinders.

DIAGNOSTIC CONDITION:
This diagnostic runs when the engine is running at a steady speed and load, and the vehicle speed is steady.

CORRESPONDING OBD READINESS MONITOR:
Misfire monitor

RESET CONDITION:
This DTC changes to inactive when the fault is no longer detected.

REPAIR VERIFICATION:
1. Clear all DTCs.
2. Test drive or operate the vehicle to meet the following conditions:
– Corresponding readiness monitor displays ‘Ready’
– Diagnostic conditions are met
– Set conditions are met
3. Did the DTC come back?
– No, repair successful
– Yes, repair unsuccessful

POSSIBLE CAUSES:
1. Faulty cylinder 4 injector (not fueling or under-fueling)
2. Loose cylinder 4 injector
3. Faulty MX Engine Brake cylinder 4
4. Symptom: Slightly reduced power:
– Incorrect valve clearance
– Large imbalance in the drive shaft
5. Symptom: Engine block vibration at high load, damaged flywheel
6. Mechanical defect (for example damaged cam follower or broken valve)

ADDITIONAL INFORMATION:
The PCI ECU can detect and identify the cylinder contribution of every cylinder based on analysis of the rotational speed of the crankshaft using a:
1. Cylinder-to-cylinder engine speed comparison and
2. A cylinder-to-cylinder rotational crankshaft acceleration comparison