Tune up your car … or your driving?

Many people take their car to the garage for service and also ask to have its engine "tuned". And garages will happily put "service" and "tune-up" on the job card … and the same words on the bill – with a separate charge for each.

It's a pleasantly reassuring little ritual, and the tune-up bit usually does no real harm, because it usually does … nothing. Ask your mechanic what a service is and you’ll get an instant tick list; ask what a tune-up is and you’ll often be answered by several moments of silence, followed by "Um…"

For there is very little that can be done to “tune” a modern engine that hasn’t already been done by a standard service … and  the designer, the manufacturer and the on-board computer management system.  And even with all their technowizardry, they can never get the job perfectly right – because what’s “right” when you start the engine is different from what’s “right” when you’re accelerating in second gear and that’s different from what’s “right” when cruising at 100 kph in 5th. “Right” differs according to the vehicle’s age, the traffic conditions, the driving style … even altitude and the weather.

Car engines, especially those with computer management systems, make some of those adjustments automatically to keep the settings as right as possible at all times.  To improve on that design would require an engineering degree, a laboratory, and quite a lot of money.  The prospects for a bloke with a spanner at kona jasho doing any better than that are not good.

What tuning basically means is optimally efficient combustion – exactly the right quantity and mixture of fuel and air, at just the right level of compression, atomized as evenly as possible, and ignited by a nice fat spark at just the right moment … according to what the car is doing at any particular instant.

Combustion is then as complete as possible, with maximum release of the fuel’s energy and minimum toxicity in the exhaust fumes. This:-

  • improves engine performance - complete burning of the fuel releases all the fuel's energy as power; unburned fuel delivers no power at all and is wasted.
  • extends engine life - the hydrocarbons and acidic gases in exhaust emissions which foul the atmosphere also clog and corrode engine parts and degrade lubricants, increasing rate of wear and risk of breakdown.
  • reduces fuel consumption - unburnt fuel is wasted fuel. Power and economy are interlinked in overall "performance".

There are many complex and highly technical factors in engine design which aim for best possible (none are perfect) combustion characteristics.     But in simple summary, each engine is designed to run best …

  • at very precise settings (mixture, ignition, timing)
  • on a very precise fuel specification

to achieve optimum power, economy, durability and exhaust purity performance.

Any deviation from the manufacturer's engine setting specifications, or precise fuel characteristics and purity, will degrade one or more or all of the performance elements.

If the mixture is too rich (too much fuel, not enough air), power output will fall, fuel consumption will rise, and emission of sooty hydrocarbons and CO will increase.

If the mixture is too lean (not enough fuel, too much air), the car will start and idle badly, it will run too hot, and there will be a substantial increase in NOx emissions.

Ignition faults or maladjusted timing (advance and retard) have similar lose-lose consequences. And in all cases, those ill-effects will apply even if the fuel is the correct specification and absolutely pure.

If the fuel itself is adulterated, the ill-effects will be even more severe, and will degrade performance even if all the engine settings are right.   For an engine designed to run on petrol, or on diesel, has no correct setting for a cocktail of petrol and kero, or a stew of diesel and kero.

Adulterated fuel causes an horrendous increase in exhaust pollution, a certain increase in fuel consumption, a probable loss of power, and  engine damage - possibly immediate, and definitely in the long-term.

So clearly, an engine in good condition, correctly set and running on the correct and pure fuel for that engine, are fundamental in the quest for reduced exhaust pollution.

But even when those conditions are achieved, there is still another basic.  How the car is driven.

The general principle is that engines run most efficiently, burning fuel most completely and producing the least toxic exhaust gases, when they are running at even and moderate speeds in the correct gear.

Any deviation from that causes an increase in the toxicity of exhaust gas. Accelerating, braking, idling, over-reving in a gear too low, labouring in a gear too high. The stop-start rhythms of a traffic jam. These can increases in exhaust pollution massively greater than design, condition or tuning defects.

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Lang’ata South Road, Nairobi
Box 15300 Nairobi 00509
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