Fuel pressure is managed by multiple systems throughout a vehicle. When a problem occurs that involves low pressure, a skilled mechanic must test these multiple systems from the fuel tank all the way into the engine block to find the culprit. By contrast, delayed shift in a vehicle is largely the province of the transmission. While easier to locate, the transmission poses a greater challenge in repair with many small parts and delicate configuration.
Delayed shift is often the first symptom of automatic transmission failure. The vehicle will struggle in gear either lurching up to the next gear or appearing to idle or slip into neutral then finding the correct gear. This delayed shift can be a sign of a mechanical issue within the transmission itself or a problem with the on-board computer not communicating the correct timing through engine speed to the transmission.
Low fuel pressure may be the result of a faulty fuel pressure regulator. The vehicle may start and run properly, though it sputters when it attempts to accelerate, or in low temperatures the vehicle will not start at all. The driver may be able to hear noise or rattling coming from the fuel pump underneath the vehicle as the regulator struggles to maintain fuel flow to the engine. Low fuel pressure can also lead to worsened fuel economy and fouled spark plugs.
Low fuel pressure may be caused by a bad fuel pump. The vehicle will idle rough, meaning the engine will seem to shudder or shake due to the lack of adequate fuel hitting the engine block. The driver will also notice this lack of fuel pressure lead to poor acceleration, lowered fuel economy and engine stalling. The fuel pump is notoriously difficult to replace; attempting the job alone, without a trained professional, may lead to further damage to the vehicle's fuel system.
Transmission fluid actually runs through a section of a vehicle's radiator, so a leak or other form of damage to that system can cause transmission fluid to become overheated and potentially damage the transmission itself. Delayed shift and gear slippage can be a symptom of a radiator problem affecting transmission fluid. This is a two-fold problem, because if it is not attended to immediately, it could lead to the replacement of both the radiator and the transmission. These repairs would carry a substantial price tag.
Inadequate transmission fluid to power the transmission's gear shifts will cause delay or slippage in gears. Typically the driver will shift into drive or reverse and the vehicle will idle for an extended period, sometimes seconds but it could be minutes, depending on how substantial the leak is. The problem could be from a crack in the transmission fluid reservoir or an issue with the transmission itself.
