Very Slight Misfire & Can't Pass Emissions

[ColinS]

When I was in my late teens I owned a Morris Minor.  Driving round a roundabout it would misfire but as soon as I left the roundabout it would run just fine.  I spent weeks changing electrical parts, even stripped and cleaned the carburettor just in case.

So one night when it happened, the roads were quiet so I stopped and lifted the lid.  Sparks everywhere.  The dipstick had swung round and was shorting on one of the plugs.  Straightened it out and never had the issue again.

The good old days of simple mechanics.

[culzean]

When I was in my late teens I owned a Morris Minor.  Driving round a roundabout it would misfire but as soon as I left the roundabout it would run just fine.  I spent weeks changing electrical parts, even stripped and cleaned the carburettor just in case.

So one night when it happened, the roads were quiet so I stopped and lifted the lid.  Sparks everywhere.  The dipstick had swung round and was shorting on one of the plugs.  Straightened it out and never had the issue again.

The good old days of simple mechanics.

Similar with Vauxhall Viva I had, opened the bonnet one damp night and it was like an electrical storm under there, nothing shorted out, this was just leakage from dodgy HT leads.  Invested in new distributor cap, rotor arm and some 'silicon' HT leads...  the lightning display went away but cant remember car starting or running any better ( but the TV picture didn't turn into a snowstorm when I pulled onto our driveway ),  those old ignition coils had plenty of power to spare - maybe to compensate for the leaky HT system.

[embee]

Yes, when you study the reliability stats for vehicles of that age the most troublesome system by far was the HT, everything from rotor arm, distributor cap, leads, plug caps, the whole business. This is one of the primary reasons why ignition systems got rid of all that junk. Of course it was also to do with more spark energy for better combustion etc, but the real force was for reliability. The first step was double ended coil packs with HT leads, but this only got rid of the distributor and left the other half of the stuff. On-plug coils offered the most reliable solution, apart from some of the dodgy coil manufacturers around in the early days. I believe modern ones are much more durable and reliable statistically.

[richardfrost]

Yes, when you study the reliability stats for vehicles of that age the most troublesome system by far was the HT, everything from rotor arm, distributor cap, leads, plug caps, the whole business. This is one of the primary reasons why ignition systems got rid of all that junk. Of course it was also to do with more spark energy for better combustion etc, but the real force was for reliability. The first step was double ended coil packs with HT leads, but this only got rid of the distributor and left the other half of the stuff. On-plug coils offered the most reliable solution, apart from some of the dodgy coil manufacturers around in the early days. I believe modern ones are much more durable and reliable statistically.

My very first car was a Morris Minor 1000, having passed my test in 1979. It was almost 'new', being a G Reg! I hammered that car up and down the M1 at ridiculous speeds for the time and car. The only time it ever broke down was coming down the hill from Shap on the M6. I was showing off to my mate how the car could show 90 on the speedo going downhill when it just completely failed on me in the outside lane. Luckily for me, given power steering and power assisted brakes were from the future, it was quite straightforward to control the car and coast on to the hard shoulder. All that had happened was the HT lead had worked it's way off as the car had tried to vibrate itself to pieces as we approached the speed of sound!

[Jocko]

A work mate many years ago had a Wartburg Knight. It had 3 coils and they all fired together (no distributor). Only the one ignited the mixture.

[culzean]

My wife's Fiat had 2 x double coils, ( 1 x 12V input 2 x HT spark outputs ) called 'wasted spark system' - this got rid of distributor which was the main problem on engines and when coil fired it produced a spark on compression stroke in one cylinder ( the useful spark ) and a spark on the exhaust stroke of its paired cylinder, that was the 'wasted spark'...

[E27006]

Wasted Spark ignition,  perfectly satisfactory, saves a half-reduction gear of a distributor, the Honda U-bone motorbikes, 110 million manufactured since the 1960s, used a wasted spark system, the magneto and contact breaker  were mounted on the crankcase and the contact breaker opened and close once per crankshaft revolution

[madasafish]

My first car was a 1929 Riley 9 Monaco fabric bodied saloon.

It had a magneto system instead of coils. Mechanical advance /retard of ignition via lever on steering wheel drove a system, of rods which rotated magneto on its mount. (Magneto generated a HT spark from a dynamo driven by engine rotation).
Occasionally it failed in hot weather. Then you replaced it with the spare . Once the original cooled down, it worked fine.

[embee]

... Then you replaced it with the spare . Once the original cooled down, it worked fine.

Haha. Yes, that's the principle of running old British bikes. Whenever you have to replace a component you put the old one on the shelf "to heal". Sooner or later it will be in a better condition than the one on the bike, and you swap them over again! 

[culzean]

The basic theory of electrickery being the flow of electrons is wrong.  Electrical equipment and cables are full of smoke,  and if the smoke escapes they stop working.