What is Sany Excavator Fault Code P304?

Fault Code P304 on Sany excavators indicates a Cylinder #4 Misfire Detected condition in the diesel engine's combustion system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects irregular combustion events or incomplete firing in the fourth cylinder through crankshaft position sensor data and combustion pressure monitoring.

This code is critical for Sany excavators because cylinder misfires directly impact engine power output, fuel efficiency, and emissions control. In diesel engines, misfires can lead to unburned fuel entering the exhaust system, potentially damaging the Diesel Particulate Filter (DPF) and turbocharger over time. For used machines, this code often signals underlying wear issues that require immediate attention to prevent catastrophic engine failure.

Common Symptoms

When P304 is active on your Sany excavator, operators typically experience:

• Rough idle with noticeable engine vibration and uneven running
• Reduced engine power and hesitation during acceleration or under load
• Check Engine Light (CEL) illuminated on the instrument cluster
• Excessive black or white smoke from the exhaust stack
• Increased fuel consumption without corresponding work output
• Engine derate mode activation in severe cases, limiting maximum RPM

Potential Causes

The most common technical reasons for P304 on used Sany excavators include:

• Faulty fuel injector on cylinder #4 due to wear, clogging, or electrical failure
• Low compression in cylinder #4 from worn piston rings, valves, or cylinder liner damage
• Damaged injector wiring harness or corroded connectors (common rub point near engine mount)
• Contaminated or poor-quality diesel fuel causing incomplete combustion
• Failed glow plug (on cold-start systems) preventing proper ignition
• ECM software glitches or corrupted calibration files
• Air intake restriction or exhaust backpressure issues affecting all cylinders unevenly

How to Troubleshoot and Fix Code P304

Step 1: Connect Diagnostic Software Use Sany-specific diagnostic software or a compatible OBD-II scanner to verify P304 and check for additional fault codes. Record freeze frame data showing engine conditions when the fault occurred.

Step 2: Perform Cylinder Contribution Test Using diagnostic software, run a cylinder cutout test to isolate cylinder #4. Monitor RPM drop compared to other cylinders—minimal drop confirms misfire.

Step 3: Inspect Fuel Injector and Wiring Remove the injector connector for cylinder #4 and inspect for corrosion, moisture, or damaged pins. Use a multimeter to check injector resistance (typically 0.3-0.8 ohms). Inspect the wiring harness along the valve cover for abrasion or shorts to ground.

Step 4: Test Fuel Injector Operation Swap cylinder #4 injector with another cylinder and clear codes. If P304 moves to the new cylinder location, replace the faulty fuel injector. For used excavators, always check for metal contamination in fuel return lines indicating injector wear.

Step 5: Check Compression and Mechanical Condition Perform a compression test on cylinder #4 (normal range: 350-450 PSI for most Sany diesels). Low compression requires valve adjustment, valve replacement, or cylinder overhaul.

Step 6: Inspect Fuel Quality and Filters Drain fuel sample and check for water contamination or debris. Replace fuel filters and water separator elements, especially critical on used machines with unknown maintenance history.

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Disclaimer: This guide provides general troubleshooting information. Always consult Sany service manuals and qualified diesel technicians for your specific excavator model. Improper repairs may void warranties or cause equipment damage.