What are the reasons for insufficient power in the FAW J6P?
4 Answers
The main reason for insufficient power is poor combustion quality. There are many factors that affect combustion quality. The details are as follows: 1. Poor fuel injection: This leads to low atomization quality, mainly caused by gum deposits in the fuel clogging the injectors and the entire fuel injection system. 2. Excessive carbon deposits: These cause varying degrees of knocking. Some mild knocking may not produce audible sounds, but the power loss is very noticeable. 3. High air-fuel ratio: The air-fuel ratio refers to the proportion of fuel to air. A high air-fuel ratio means there is too much air and too little fuel during mixing, which naturally results in insufficient power. The air-fuel ratio is automatically adjusted by the computer system based on combustion quality. When the system detects poor combustion quality, it increases air intake to ensure proper exhaust emissions. Therefore, as gum deposits in the fuel injection system and carbon buildup in the cylinders gradually accumulate, the computer system will progressively increase the air-fuel ratio due to worsening combustion quality, leading to a gradual decline in power. This is a gradual process. To maintain the air-fuel ratio at its optimal level, it is essential to keep the engine's fuel injection system and combustion chamber clean, ensuring high combustion quality for consistent power output.
Last time, several J6Ps in our fleet also had sluggish power. I spent several days at the repair shop figuring it out. The most common issue is clogged fuel injectors. China VI vehicles have high requirements for diesel, and using fuel from small gas stations can easily cause problems. Another issue is not replacing the air filter on time—when the engine can't breathe properly, it naturally lacks power. I've personally seen vehicles with stuck EGR valves where the RPM wouldn't go up even with the throttle floored. Turbocharger leaks are also a common problem; if you hear a hissing sound, be alert. If the turbo pressure sensor fails, the ECU directly limits the power. Drivers operating in Yunnan, Guizhou, and Sichuan should pay special attention to the diesel filter—the large altitude changes put more strain on the fuel pump. After replacing the filter, the power comes back—it's a small cost to solve a big problem.
Driving trucks for twenty years, I've encountered all sorts of power loss issues. The FAW J6P's engine wiring harness is prone to water ingress and oxidation, especially the connectors behind the cab, which often have poor contact after rainy days. Exhaust pipe blockages are deadly; when the DPF in the aftertreatment system gets clogged, you can clearly feel the exhaust flow is restricted. Clutch slippage is the most frustrating, with engine RPM soaring but the vehicle speed not increasing when climbing hills with heavy loads. Crankshaft position sensor failures are more insidious—the dashboard might not show any warning lights, but power drops by a third. Once, the fuel tank's intake pipe got kinked, creating a vacuum in the tank that prevented fuel from being drawn, making even level road driving difficult. I recommend checking the throttle pedal position sensor; using a diagnostic tool to read the data stream is far more effective than guessing blindly.
Just finished repairing five J6P trucks with insufficient power, and identified three common failure points. First, air leakage in the low-pressure fuel line—aging seals on fuel pipe connections can allow air into the diesel pump, causing fuel cuts during uphill climbs. SCR urea nozzle crystallization also triggers torque limitation; the dashboard won’t show errors, but acceleration feels sluggish. Excessive engine oil in the oil pan similarly impacts power—exceeding the dipstick’s upper limit by 2 cm noticeably makes the engine feel stifled. I always remind fellow truckers not to overlook faulty fuel tank water level sensors, as the ECU mistakenly limiting power output when misjudging water in the tank.
