Why won’t my car start?

Thursday July 18 2019

 

By Paul Kaganzi

Hello Paul, my Toyota Corolla with a 5A engine suffered a broken timing belt. My mechanic replaced the timing belt and the car was test driven. However, the engine has failed to start. The mechanic has replaced the fuel pump and now says it is the distributor. What do you think is the cause? Baguma

Hello Baguma, there are several factors that can lead to failure of an engine to start. Broadly, I will categorise them into engine management system, fuel system, ignition system and air intake system. The engine management system (EMS) relies on the engine computer to control the amount of fuel injected and ignition timing.

This system relies on sensors such as the crank shaft and camshaft position sensors as well as the coolant temperature sensor to help it know when to deliver sufficient fuel and spark for efficient engine combustion.

A breakdown of any of these sensors can prevent the EMS from starting the car or running smoothly. The EMS performance and health can be investigated with a computer diagnostic tool. The fuel system delivers sufficient fuel pressure for prompt ignition. I see your mechanic has looked into it by replacing the fuel pump.

A faulty fuel pump can cause a no start condition. Did your mechanic fit a new pump and has he measured the fuel pressure and compared with recommended values?
The fuel filter should be replaced and the performance of fuel injectors also be assessed. The ignition system in your Toyota 5A petrol engine generates a spark or heats an electrode in the spark plugs to ignite the fuel air mixture. This system on your car engine works with the distributor which allocates the spark, ignition high tension leads and the spark plugs. These three must be investigated to ensure that they work well. Having replaced the engine timing belt, it may be a good idea to confirm that the engine timing was correctly done using the manufacturers’ timing reference marks.

Failure to get the timing right, either retarded or advanced will affect ignition or spark timing. This can prevent prompt starting or cause poor performance. It is also prudent to confirm that the distributor was timed well and not damaged after timing belt renewal. A compression test is also in order to confirm that there is sufficient compression to start and run the engine.

The air intake system is broad but investigate the intake hoses for air leak between the air filter and throttle potentiometer. Inspect the throttle potentiometer and rule out a carbon clogged or stuck throttle valve. You need a patient and knowledgeable mechanic to investigate and pinpoint the problem. Let me know how it goes.

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