Electronic ignition means less DIY

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IOL mot pic feb7 Multi-Change Ignition

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An electronic multi-change electronic ignition system designed for direct-injection petrol engines.

Back in the days when men were men (well, mostly) and women were women, cars and motorcycles were easy to service and even rebuild.

Things to consider were mechanical rather than electronic, and if you could get a spanner, a screwdriver – or even a hammer – to it you were home and dry.

Take ignition timing as an example. With the contact-breaker points (coil, magneto or magneto-dynamo) systems the timing could be determined first by setting the gap with a feeler gauge then, with a cigarette paper between the closed points, cam-ring in the fully advanced position and piston rising on compression stroke, the paper would just come free as the points began to open, thus pin-pointing the timing.

If the point of opening was not at the required distance before TDC, the points would have to be repositioned.

Early sports car engines mostly used magneto ignition.

The faster engines of the day could reach 5000rpm or more but the coil ignition systems of the period could not be relied upon to maintain sufficient voltage at such engine speeds.

Let’s go back in history a bit.

The pre-war rotating armature magnetos developed high centrifugal stresses in their windings, but could cope up to about 6000rpm in a four-cylinder engine.

We have to bear in mind that the magneto is more efficient at high speed than it is at low.

With coil and contact-breaker points, about 0.01sec was required for the current to build up to full value, and this could occur only when the points were closed.

The snag was that at high revs with the old coil and distributor types then available there was a big drop in voltage value, about one third of low-speed value.

The problem of achieving good ignition at both high and low engine speeds in expensive sports cars was solved by using two plugs for each cylinder - one was sparked by a magneto and the other by an ignition coil.

A brilliant purely mechanical solution perhaps, but it worked.

Electronic ignition eventually replaced the points and condenser systems and you didn’t have to be a rocket scientist to understand it.

Then we had the complex, if far more efficient, microcomputer control of ignition advance angle for every plug firing.

Goodbye to the spanners and hammer. Mechanical systems relied on centrifugal weights to advance timing and a vacuum diaphragm via manifold pressure would change timing advance too.

The snag is that once these methods have reached their limits, advance control is fixed.

Now, in the quest for optimum power, fuel economy and fewer nasty emissions, thousands of data points from dynamometer tests and road tests under varying speed, load and temperature conditions are carried out and recorded on data “maps” and stored in the read-only memory.

The control unit uses this data to ensure the best ignition timing for engine load and revs at all times. Progress, of course is a double-edged sword; we have increased engine efficiency, but less scope for DIY and more expense when things go wrong.

Excuse me, I have to go out and feed my horse. - Star Motoring


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