Ask the Mechanic

Justine Juliet

Hello Justine, a car engine stalls when it stops running suddenly and sometimes unexpectedly. This will cause a pre-start condition display of all dashboard lights. Engine stalls can be quite scary or sometimes hazardous to you and other road users. There are several causes of car engine stalling usually related to a breakdown of fuel, ignition, air intake, engine management or the cooling systems. An inspection in the garage will help to determine the faulty system.

Fuel system failure is usually a result of the fuel pump breakdown. This device pressurises and delivers fuel from the tank to the engine, it can breakdown due to a dirty, blocked fuel filter, corrosion in the tank or ageing. Similarly, dirt can affect the fuel injectors which will get blocked and fail to deliver the required fuel pressure. Another scenario is running out of fuel due to a faulty fuel gauge.

The Air intake system fails when ample air is not delivered to facilitate required ratios of fuel air mixture. The resultant engine rich running condition (more fuel than air) will negatively affect combustion (fuel burning) and engine running causing stall or poor performance. Air intake failure can be caused by a dirty clogged air filter, leaking intake pipe after the air flow metre, a dirty or faulty intake throttle valve.

Faulty engine management components such as sensors (air flow metre, crank shaft and camshaft and throttle position sensors. or the engine computer can cause a failure to deliver ample fuel or spark if they are not working well.

Ignition system failure will also cause engine stall. The ignition system delivers spark to ignite the fuel air mixture. It can fail when the circuit of the ignition coils or spark plugs are faulty. An inspection at the garage can quickly determine if it is the culprit and isolate which of the system components are faulty. Occasionally, the engine cooling system can cause stalling when the engine overheats. Often, it is a result of engine fan or water pump failure. Other times, leakages on the radiator or plumbing pipes will cause overheating.

IS MY CAR’S FUEL PUMP FAULTY?

Hello Paul, lately, my Toyota Harrier petrol engine has delayed cold starts, hesitation when I accelerate and a few days ago started stopping in traffic jam. A routine inspection indicates that all is well. My cousin says it might be the fuel pump. How can I be sure?

Kaggwa 

Hello Kaggwa, your cousin might be right. The symptoms you describe are similar to those of a failing petrol fuel pump. A fuel pump is designed to deliver fuel at a suitable pressure from the tank to the engine. The fuel pump for many modern petrol driven cars such as yours is fitted in the fuel tank.

Some of the common symptoms of a failing fuel pump include a high-pitched whining noise instead of a quiet humming sound and this will be heard when the fuel pump starts to fail. This may be followed by hard starts. A good fuel pump pressurises the fuel system and helps it to start promptly while a weak pump causes delayed starts.

Engine hesitation or sputtering may be experienced at higher speeds. Fuel pump failure often causes stalling after engine warm up. A bad fuel pump leads to power loss during acceleration, which is due to failure to sustain the demand for increased fuel pressure. This may result in engine surge or hunting. When the pump completely breaks down, it will cause failure to start.

There are fuel pressure tests that can be carried out in a garage to determine the working condition of your fuel pump. To help protect your fuel pump, carry out the Toyota recommended replacement of the fuel filter at 100,000kms.

Also, keep your fuel system clean by refuelling with reputable petrol fuels, which keep the fuel system clean to prevent accumulation of harmful and efficiency-robbing corrosion and dirt.

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