As engineers squeeze every bit of energy out of a droplet of fuel, every element under the hood is operating on a razor’s edge of a potential drivability diagnostic problem. For example, a little bit of carbon on an intake valve can cause the air going into the combustion chamber to be turbulent and cause some of the fuel to condense and burn unevenly, or a small vacuum leak could cause unmetered air to enter the combustion chamber. Even a small change, like the amount of pressure delivered by either the fuel pump in the tank or the high pressure pump on the engine can have implications for emissions and drivability.
Port fuel injection motors compensated for these issues because they were expected to be somewhat inefficient. They had lower compression ratios and larger catalytic converters. As a result, small input and changes in the combustion event really didn’t matter in the overall picture, but with GDI, the performance of every pump, sensor, and actuator matters. Worn parts and missing maintenance can cut into the drivability diagnostic margins. For example, let’s say you have a vehicle with a P0171 for lean long-term fuel trims. One cause could be wear to the camshaft and follower of the high pressure fuel pump. Small amounts of wear to the surfaces can directly affect the stroke of the pump. If the stroke of the pump is changed, the amount of pressure the pump can generate is altered.
For both the carbon deposits and wear problems, there is one root cause, the engine oil. With carbon deposits, low quality oil typically has a higher percentage Noack rating for evaporative losses. This is also referred to as oil volatility. When oil evaporates, it leaves behind carbon that can form deposits. Also, low quality oil may not have an adequate additive package to protect the surfaces of the camshaft or follower on the high pressure fuel pump. But even the best oil can’t protect the engine and high pressure fuel pump if the oil is not changed regularly. The point is that you should leave no stone unturned before you run out of diagnostic labor. Even if the high pressure fuel pump has failed, minor problems in other components can cause a major comeback. Thanks for watching.
This video is sponsored by Carter Fuel Systems.