Ask the Mechanic

Thursday February 25 2021
By Paul Kaganzi

Why does my diesel car lose power? 

Hello Paul, I own a Toyota Land Cruiser HDJ. Lately, while in motion, the engine loses power especially when going uphill. I also use a lot of energy on the accelerator to gain the necessary speed. What could be the issue?


Hello Katutsi, your 4.2 litre diesel HDJ Toyota Land Cruiser loss of engine power uphill is most likely a result of low fuel pressure. There are other factors that can reduce a diesel engine’s performance such as low compression (if it leaks oil internally due to worn out piston rings), a restricted or leaking air intake system, a leaking or faulty vacuum system and blocked emission system.

Fuel pressure is crucial for a diesel engine’s performance, especially because it uses compression ignition. Critical fuel system components to inspect are the fuel injectors (clogged or leaky), fuel lines (leaky), fuel filter (dirty/clogged) and the fuel pump in case its flow rate or pressure is below par. You may need a diesel fuel specialist to test the fuel injectors.

Failure to regularly service your fuel filter or use of adulterated diesel can also cause fuel system component failure. A computer diagnosis and knowledgeable technician can monitor actual fuel pressure values and compare with recommended values. The critical performance components in the air intake system are the turbo charger and intake hoses. These can be examined for performance problems or leaks. Use of recommended engine oil is critical for turbo charger lifespan.


A damaged turbo leaks oil and fails to boost intake air pressure. The air cleaner element should also be inspected. If your engine lubrication system is faulty due to a poor oil service regime, it can lead to damage of the piston rings, besides other fast moving components. The ensuing internal oil leak causes a loss of engine compression, which is critical for engine combustion (burning fuel).

My car makes noise during gear shifts

My Toyota Corolla G (2001) makes a knocking sound when changing gears, especially when it heats up. What could be the cause and how do I resolve it?


Hello Peter, your Toyota Corolla is experiencing difficult transmission shifts. When shifting, you probably feel a jerk and hear a thud. The common causes of this problem are low automatic transmission fluid (ATF) level,  ageing ATF fluid and damaged electrical or mechanical components.

ATF plays an important performance and protective enhancing role in a car’s automatic gearbox. Besides building vital hydraulic pressure to engage gears, ATF lubricates, cools, prevents corrosion and seizure of metallic components. When ATF levels are low due to a leak on the transmission or cooling system, you will experience violent or noisy gear shifts. This not only affects performance but also causes damage to the gearbox.

Use the ATF dipstick to confirm the fluid level. If found below recommended level, a mechanic should identify and stop the leaking point.

ATF quality is important for the above mentioned protective and performance enhancement functions. When ATF ages, it can reduce transmission performance as well as fail to protect it.

ATF should be renewed periodically and the gearbox filter replaced to allow prompt ATF flow after it is filtered. Occasionally, an automatic gearbox will suffer mechanical or electrical damage due to prolonged use with low oil levels or delay to service the ATF.

Where damage may exist, a computer diagnosis or physical inspection in a garage will help to confirm what is faulty.


Can I improve my car’s efficiency?

I have a Toyota Prado 2, 1994 model which is automatic. I have been told that I can improve its efficiency by converting it to a manual transmission. What does this entail and will it affect its performance?


Hello, there are credible grounds to argue that a car with a manual transmission can sometimes be more fuel efficient than one with an automatic transmission. However, there is a disclaimer to that. The driving style matters, even with the manual transmission. For example, timely gear shifts and non-aggressive driving, the vehicle engine, transmission and tyres must be in a good running condition to help achieve that efficiency.

On the other hand, vehicles with automatic transmission have been built with fuel efficient and performance enhancing technology such as variable valve timing, direct electronic fuel injection, continuous velocity transmission as well as cruise control systems. All these innovations, if used and maintained well, can improve the efficiency of an automatic transmission. Sensible driving and general condition of the car also count.

To convert your car’s gearbox system from automatic to manual, you will need; a smart technician to do the gearbox conversion, a suitable replacement manual gearbox new or used; a new set of pedals, gear linkage and shift stick; flywheel, a complete clutch kit and fork assemblies.

It may be necessary to replace the engine management computer and throttle unit (in case it is a petrol engine) with suitable replacements which are configured to work with a manual transmission. If the required components are secured and the conversion done correctly, the car’s performance should be good.

Send sms: mycar (space) your comments and questions to 6933 Or email them to: