If rail pressure is too low, what is a likely outcome?

• A. Increased engine power
• B. No effect on combustion
• C. Poor spray pattern and misfires
• D. Fuel economy improves

Answer: (C)

Rail pressure sets how finely the fuel is atomized by the injectors. When the pressure is too low, the injector can’t produce a proper spray—the droplets are larger and the spray pattern is poor. That leads to incomplete mixing with air and potential ignition problems, causing misfires. With misfires and inefficient combustion, engine power typically falls and fuel economy worsens. So the most likely outcome is a poor spray pattern and misfires.