How to Tell if the Return Oil Valve is Faulty?
2 Answers
To determine whether the return oil valve is functioning properly, you can disconnect the vacuum valve to test the return oil. The return oil valve typically uses a vacuum valve; the greater the vacuum, the more the valve opens, resulting in more oil return. The return oil valve, also known as the fuel pressure regulator, can get stuck in the closed position when damaged, leading to excessively high fuel pressure. High oil pressure causes an overly rich air-fuel mixture, resulting in issues such as increased fuel consumption, black smoke from the exhaust pipe, insufficient power, and difficulty starting the engine. The return oil valve serves a pressure-relief function. In a quantitative pump throttle adjustment system, the quantitative pump provides a constant flow. An increase in system pressure reduces the demand for flow.
After running an auto repair shop for so many years, I've encountered numerous cases of faulty return valves. Simply put, to determine if it's bad, you need to check for obvious symptoms in your car. The most common issue is diesel leakage. After parking, crouch down and inspect the area near the fuel tank for oil stains or wet spots, especially around the return valve connections. While driving, if you notice engine shaking or power loss—such as unsteady acceleration or difficulty starting—these are clear indicators. A sudden increase in fuel consumption suggests the valve is either clogged or not sealing properly, leading to poor fuel control. For a DIY check: open the hood and feel the return valve housing; if it's abnormally hot, internal leakage might be occurring. Listen for a hissing sound during operation, which indicates high-pressure fuel leakage. If all these signs are present, the valve is likely faulty. Don’t delay—replacing it costs a few hundred dollars, and a bad valve can damage engine components. It's best to have a professional mechanic test the fuel pressure for confirmation.
