1. Vehicle Overview
The Dongfeng EQ1141G heavy-duty truck is widely used in transportation industries. It is equipped with a Cummins diesel engine and a VE single-plunger distributor fuel injection pump. Although this engine is durable and reliable, long-term heavy-load operation commonly causes power drop, slow acceleration, and poor high-speed performance. This article shares real maintenance cases, failure causes, inspection methods, and professional repair solutions.
2. Typical Power Failure Cases
Case 1: Low speed normal, insufficient power at high speed
During inspection, the fuel pump plunger showed minor wear. All mechanical parts were in good condition. After bench testing, technicians found that low and medium-speed fuel delivery was normal, while the fuel volume remained the same whether turbocharging was activated or not.
Root Cause: The turbocharger compensation pin was stuck. Under high-speed heavy-load conditions, the turbocharged engine requires extra fuel to match increased intake air. When the compensation pin cannot move freely, extra fuel supply fails, resulting in weak high-speed performance.
Repair Method:
- Add lubricating oil to the diaphragm chamber;
- Push and move the correction pin repeatedly until flexible;
- Clean internal oil contamination with diesel;
- Reassemble and calibrate on the test bench;
- Road test confirmed strong high-speed power recovery.
Case 2: Sudden slow acceleration & obvious power reduction
A Cummins 6BT engine on Dongfeng EQ1141G experienced sudden acceleration delay. After disassembling the VE fuel pump, two critical damaged parts were found: broken plunger spring and cracked buffer rubber blocks between the transmission shaft and governor gear.
The damaged components caused plunger tilt, which affected the flexibility of the fuel control sleeve. Finally, the engine showed slow acceleration and delayed speed reduction.
Solution: Replace the plunger spring and buffer rubber blocks. Recalibrate the fuel injection pump. After installation, the engine regained sensitive acceleration and stable power output.
3. Common Symptoms of Diesel Engine Power Degradation
- Weak engine power, poor climbing performance;
- Hard cold start;
- High fuel consumption;
- Black smoke and dull exhaust sound;
- Abnormal mechanical noise;
- Slow speed increase even when stepping on the throttle.
4. Main Failure Causes & Maintenance Solutions
1. Poor Cylinder Sealing Performance
Use a cylinder pressure gauge to test each cylinder. Inspect valves, valve seats, pistons, piston rings, and cylinder liners. Replace damaged gaskets, deformed cylinder heads, and cracked components to restore compression tightness.
2. Reduced Compression Ratio
Excessive valve sinking reduces compression efficiency. Replace valves or valve seats. Repair or replace deformed connecting rods to maintain standard compression ratio.
3. Abnormal Single-Cylinder Operation
Judge faulty cylinders by temperature detection, sound judgment, and cylinder cut-off methods. Common problems include air in fuel lines, worn plungers, and poor injector atomization. Drain air, replace aging springs, clean injector carbon deposits, and adjust injection pressure.
4. Incorrect Injection Timing
Advanced or delayed injection leads to incomplete combustion. Recalibrate fuel advance angle. Replace severely worn plungers and delivery valves to stabilize injection timing.
5. Insufficient Fuel & Air Intake
Check pipelines from outside to inside. Replace clogged filters, repair air leakage, and recalibrate the governor to ensure stable fuel and air supply.
6. Incorrect Valve Timing & Valve Clearance
Worn camshafts reduce valve lift and shorten intake/exhaust time. Adjust valve clearance above 0.2mm to avoid air leakage. Replace severely worn camshaft assemblies.
7. Poor Lubrication & Cooling System
Clean oil filters, replace engine oil, and inspect oil pumps. For overheating failures, clean radiator scale, check fan belts, water pumps, and thermostats to maintain optimal working temperature.
5. Other Hidden Influencing Factors
Excessive combustion chamber carbon deposits and moisture in diesel fuel also cause power loss. Regular carbon cleaning, water separation, and high-quality diesel usage can effectively extend engine service life.
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