ASK THE MECHANIC: My car stops suddenly

Hello Paul, I own a Mitsubishi Pajero with petrol engine 3.5 l V6. All has been well until it started stopping suddenly, especially when driving uphill or in traffic. I was advised to replace the fuel filter but the fault persists. A computer diagnosis reported the fuel rail pressure sensor which I bought and a mechanic replaced it but there is no change. What could be the problem? Job

Hello Job, when a diagnostic test with a computer picks up the fuel rail pressure (FRP) sensor fault you ought to first investigate the fuel rail pressure before concluding that the sensor is faulty. You may have a faulty fuel pump.
The fuel rail pressure sensor is an engine management component that monitors engine fuel rail pressure and shares that information with the engine computer which uses it to adjust fuel delivery and timing. When you have a faulty high pressure or primary fuel pump, the fuel rail pressure on your GDI engine will drop significantly. The fuel rail pressure sensor will communicate this status to the engine computer which will adjust engine timing or fuel delivery.
That said, a faulty fuel rail pressure sensor will send wrong signals to the engine computer and lead to the same symptoms of hard starting, loss of acceleration, poor performance and sometimes the check engine light. Perhaps that is why the mechanics drew the conclusion to replace the FRP sensor.
An engine fuel pressure test will quickly confirm whether the primary or high pressure fuel pumps are faulty. This should put an end to your misery. Delay to replace the fuel filter is a common cause of fuel pump failure.

What causes unstable idling?

Hello Paul, my 2003 Nissan Maxima 2.5 litre V6 petrol has unstable idling and poor performance. I have changed spark plugs, air cleaner, fuel filter and ignition coils. I have even cleaned the throttle and tried out different fuel stations thinking it is a fuel problem. Kindly let me know what could be the problem before I give up on this nice ride. Julius

Hello Julius, do not give up yet. Having ticked almost all the inspection boxes, you need to ask the mechanic to examine the Nissan engine for a possible vacuum leak. Engine vacuum is generated from the internal combustion blow by gas and harnessed through the engine positive crank case ventilation valve. This vacuum helps to stabilise the engine during running and will play a significant role in smooth performance and fuel efficiency.
Overtime, leakages will develop as the vacuum hoses at the throttle potentiometer, intake manifold, vacuum solenoids or the brake booster become warped and cracked by the engine heat, age or oil leaks. In the absence of a vacuum gauge or tester a mechanic can use observation and tighten or replace all damaged vacuum hoses. Also ensure that that the intake manifold gasket does not leak due to damage.

My car does not brake

Hello Paul, I own a Toyota Allex which has developed a light rumble when I apply brakes. The car’s brake pedal feels soft and does not brake immediately. I have replaced brake pads, brake discs and the master cylinder but the problem persists. What is the problem? Muwonge

Hello Muwonge, its an open and shut case. You will need to check for dirty ABS wheel speed sensors or replace the Anti Lock Brake System (ABS) modulator. You will also renew brake fluid and bleed the brake fluid system. A good mechanic needs to be engaged to do this work. The ABS modulator re-routes and channels brake fluid to all four wheels after its pressurised by the master cylinder. ABS delivers hydraulic pressure to the brake callipers in a pulsating motion to prevent wheel lock when a car is skidding.
The four ABS wheel speed sensors constantly update wheel speed information to the ABS module. Ordinarily when you brake on a firm surface ABS should not kick in so you should not experience a pulsating motion on the brake pedal. In the event that you keep experiencing a pulsating or juddering sensation whenever you brake, it means the ABS system (modulator and sensors) need to be inspected or replaced. A computer diagnosis also helps to rule out electrical failure of the ABS system (relay, circuit and control module).

My steering wheel hardens after hours of driving

Hello Paul, I drive a Nissan Teana model 2003. In the morning, the steering is soft and swift, but after some hours of driving, it starts hardening. It has also started making a sound when turning while in motion. What could be the problem? Henry

Hello Henry, you most likely have a failing steering pump and aged steering hydraulic fluid. A steering pump uses an engine driven belt and pulley system to deliver pressurised hydraulic oil to the steering gearing in the rack or steering box. This hydraulic effect makes your steering feel light as you operate it despite carrying the load of the car on its front wheels.
The efficiency of the steering pump relies on the service condition (viscosity) of hydraulic fluid and the operational state of the pump itself.
Steering hydraulic fluid ages due to heat, frictional wear of metallic components and accumulation of deposit. This reduces its viscosity or thickness and ability to build hydraulic pressure which is used to power or carry the load on the steering system. This could explain the changing performance at different temperatures. Also, rule out a severe hydraulic fluid leakage due to damaged hoses which can lead to pump failure.
Delayed fluid service or leaking hydraulic hoses will damage the steering pump vanes and squealing or screeching noises or intermittent hard steering are common symptoms as it fails.
Consider replacing the steering pump and hydraulic fluid.

What is the downside of a Toyota Duet?

Hello Paul, I would love to buy a Toyota Duet but I have been discouraged by a mechanic who says it presents very many issues mechanically. Are such issues difficult to fix? Tukundane.

Hello Tukundane, the Toyota Duet or Daihatsu Storia is a sub-compact mini hatch car with no generic or characteristic mechanical problems. Built fromm 1998 to 2004, it is famous for its fuel efficient 1.0 and 1.3 litre engines. Being a Daihatsu, the Duet does not have ready availability of mechanical and body repair parts either new or used, like main stream Toyota vehicles do. Maybe poor parts availability is what troubled your mechanic.
The other challenge might be a procurement one. The profile of customers who drive the Duet or Storia are budget-conscious. A few of them also ‘cut corners’ when it comes to maintenance. When buying a used Duet, like any other used car, you need to have it checked thoroughly to ensure that you do not buy one with a poor maintenance record. Follow your heart and buy the Duet, after ascertaining its technical condition.