Ask the Mechanic: Why does my car stop when gear is engaged?

Hello Paul, lately, when I start or engage any gear on my 1998 RAV4, the engine stops. In order to drive it, I either have to ask someone to push it as I engage the gear or step on the acceleration immediately after engaging the gear. When I slow down to a near stop, the car stalls and I have to go through the same process again. What could be the problem?

Wilfred.

Hello Wilfred, your car engine stalling when you engage the gear is probably due to an engine tuning issue. There are a few issues that cause an engine stall or engine tuning problems and these include a faulty idle control valve, leaking vacuum, faulty sensors, fuel delivery problems, ignition system malfunction or mechanical faults such as engine compression loss.

The idle control system, attached to the throttle unit, helps to maintain stable idle of the engine when you engage gear or during running. If the system is faulty or clogged with corrosion or deposits, it will not work well and can cause an engine stall when you engage drive.

Vacuum leaks on your engine will affect the air fuel ratio, which in turn causes engine stall or poor running. Another cause are faulty sensors such as the throttle position and mass air flow sensors which help the engine management system monitor and regulate fuel and spark delivery. When these sensors fail, they can cause engine stall.

Restricted fuel delivery due to failure of the fuel pump, dirty fuel filter or injectors can also cause engine stall. A faulty ignition system, which includes coils or spark plugs will cause poor performance and engine stall. If your engine is suffering from low compression due to worn out piston rings it will lack power, when you load it with gears it can stall. To verify which one of these issues is causing the engine stall, find a suitable garage with the diagnostic tools and expertise required to isolate and fix the problem.

SHOULD I ALWAYS DEPRESS THE CLUTCH BEFORE STARTING?

I am told I should always depress the clutch before turning the start key.  Why is this necessary?

John

Dear John, depressing the clutch of a manual transmission car before starting it is both a safety and mandatory procedure, depending on the generation of car you drive. Depressing the clutch with your foot helps to disengage the drive train when you turn the engine during start mode. Technically, depressing the clutch separates the pressure plate from the clutch disc, which interrupts engine power flow to the drive. 

This is a safety procedure intended to prevent the car from lurching backwards or forwards in the event you forgot to engage neutral or left the gear shift stick in reverse or any forward gear. In older manual cars and a few newer ones, it was considered safe and best practice to depress the clutch before turning or starting the engine. However, it was not mandatory as long as you ensured that the gear lever was in neutral position.

In many modern cars, especially those fitted with the automatic start stop traffic emission control feature, you need to depress the clutch to get starting enabled.

Generally speaking, consider depressing the clutch before starting as a safe best practice whether you are driving an old or modern car.

WHAT ARE TURBO TIMERS?

What are turbo timers for and do engines really need a cooling-off period?

David.

Turbo timers are electronic gadgets fitted on motor vehicles whose engines are turbo charged in order to keep the engine running for a specified time before switching itself off, even after you manually switch off. This is intended to allow turbo cool down before the engine stops.

It is important for the engine to run at idle speed for a few minutes to allow the turbo intake and exhaust compressors to cool down. Idling the engine while the turbo cools or slows down after a hard run, allows engine oil to continue circulating and protecting the fast spinning turbo from damage due to dry running when you suddenly stop the engine. Switching off the engine after hard running can also lead to trapping of hot oil between the turbo compressors. This oil can cause deposit formation which can damage the turbo bearings and seals in the long run leading to turbo failure.

The other pertinent question is whether every car with a turbo should be fitted with a turbo timer? The answer is no. Turbo timers are useful in preventing premature shutdown of the engine to allow it cool down, especially for the impatient driver. However, they may not be necessary if the driver conscientiously lets the engine run at idle for a minute or so to allow cool down before they switch it off.

WHY ARE INDICATORS ON NEWER CARS BARELY VISIBLE?

Please help me understand why some exterior lights on newer cars are so small. Some indicators are barely visible, especially in bright sunlight, and I wonder how many accidents or near-accidents are being caused by our inability to see where other motorists are heading. Is there not some sort of legal standard whereby indicator lights actually have to be visible to other motorists?

TK. 

Dear TK, exterior lights on newer and modern cars have become smaller, especially with the advent of the Light Emitting Diode (LED) lights technology. LED is a semiconductor diode that glows when supplied with specified voltage. They are fancier looking, fit easily in modern headlight or tail light design and arguably less energy consuming.

However, during the evolution of the LED lights, the earlier models first fitted with LED lights had indicators installed in small spaces. These are not easy to see, especially when the sun is bright and could cause accidents.

Car manufacturers must have addressed the poor visibility of LED indicators experienced on earlier models. Newer and more modern cars today have bigger LED indicators and some of them are built with sequential indicator lights which have five or more indicator light segments on each side of the head lamps and tail lamps.

Each of the indicator LED light segments flash one after the other instead of the conventional indicator light bulb that flashed at once. This is eye catching. The car manufacturers submit to legal lighting legislations abroad.

The road safety act of Uganda talks about legal street lighting in as far as cars having manufacturer fitted visible head lights and tail lights. Globally, all countries’ highway codes and tax guides talk about legal lighting to guide car manufacturers and enthusiasts. All car manufacturers submit to the department of transport, an international organisation which regulates car lights as well as tyres.

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