Why doesn’t my car accelerate fully?

Thursday March 21 2019

The fuel filter should also be replaced because

The fuel filter should also be replaced because a clogged fuel filter will damage even a new fuel pump. 


Hello Paul, I drive a 2003 Toyota Mark X with a mileage of 160,000kms. Overtime, it has gradually been losing power. I recently changed the spark plugs and air cleaner. A few days ago, it started cutting power after driving for a short distance. It fails to accelerate fully and can only drive slowly while misfiring and the engine almost cutting off. There is no check engine light. What could be the problem? Mark

Hello Mark, sounds like you have a fuel supply pressure problem. The absence of a check engine amber light means that the fault may not be engine management related (sensors and computer) but it does no harm to carry out a computer diagnosis. It would be good to evaluate the fuel pressure using a fuel pressure gauge and compare results with the recommended nominal values. This will confirm my hunch that the fuel pump has failed and not any of the other engine management components that cause similar or related symptoms.

The fuel filter should also be replaced because a clogged fuel filter will damage even a new fuel pump. A fuel pump pressurises the fuel system and helps to pick and deliver fuel from the tank to the fuel injectors in the engine. This process requires precision both in quantity or fuel pressure terms. It is a lot like turning on your water tap and getting a weak flow of water when the pressure drops. Gasoline fuel pumps usually last beyond 150,000kms. Failure to replace a restricted and dirty long life fuel filter at 100,000kms, as recommended by the car manufacturers, will damage the fuel pump as it works harder to deliver fuel through a clogged fuel filter.

Symptoms of a failing fuel pump include a loud whining noise, hard starting, engine hesitation or faltering when you accelerate, stalling at high temperatures, loss of power under stress, as well as erratic engine idling or surging and awful smell from unburnt fuel in exhaust fumes. In extreme cases of total fuel pump failure, the car will not start.