cylinder not firing, reasons?

firely2327

In short, had an issue with the engine light flashing then staying on permanently while away from home in my ford fiesta two weeks ago. Recovery vehicle arrived courtesy of insurers and told me that the third cylinder wasn't firing correctly and I should therefore get a new coil pack asap. Did so when I arrived home and fitted via local mechanic.


The engine light has started to come on again and the car is sluggish when this happens. Wondering whether the diagnosis of the recovery team was correct re the third cylinder and if so what apart from the coil pack could be the cause, the sparks? Want to go to a garage with at least half an idea so I don't get taken for a ride......... Ta

forgotmyname

When did it have a full service including spark plugs and leads etc?

Fouled or faulty plug. leads faulty. Then you get down to cylinder issues,
oil passing the rings broken rings etc etc etc...

You dont tell the garage whats wrong, that is their job.

rich13348

Spark plug, HT lead, fuel injector, faulty new coil pack. Take it to a garage and have them do their own analysis and fix the fault.

facade

One reason why coil packs fail so often is that no-one bothers to change spark plugs anymore. When the plug is dirty, or just plain worn out the coil has to work harder and fails.

Doesn't help that in The Olden Days you could actually see the plugs to change them, whereas now most of the engine has to come apart.

try new plugs.

Strider590

facade wrote: »

When the plug is dirty, or just plain worn out the coil has to work harder and fails.

As above.

For every 0.2mm of wear on the spark gap, the coil has to output an extra 5000 voltages to overcome that gap, it's very easy to overheat and damage a coil by having worn plugs.

If you speak to a mechanic, they may or may not know this (they tend not to knwo the engineering/theory behind what they do), if you speak to some guy in a suit, he won't have a clue and he'll probably try to tell you it's nonsense.

They're easy to gap yourself, by placing a feeler blade of the correct thickness between the electrodes and very lightly tapping the plug on a hard surface until the blade has been lightly pinched, but in all likelihood this won't help for long on old/worn plugs.

It's not the only thing that can cause a coil failure, but it's probably the most common.

AdrianC

There are four coils, on four plugs, in four cylinders.

All four were new at the same time. One has just failed and been replaced.

That leaves three of the same age as the one that just failed, doesn't it...?

Strider590

AdrianC wrote: »

There are four coils, on four plugs, in four cylinders.

All four were new at the same time. One has just failed and been replaced.

That leaves three of the same age as the one that just failed, doesn't it...?

In theory yes and I think if it were me i'd replace all four for the sake of it, but in practice there are many other factors to take into consideration, something as simple as a badly designed engine cover or a badly routed coolant hose, anything can be a factor in increasing stress on one of 4 identical components.

almillar

All of the above looks good.
Age and mileage of car?
Age and mileage at which car is meant to have its spark plugs changed?
Put those two together...

tedted

what fiesta has individual coils,we dont know the year or engine size

Strider590

tedted wrote: »

what fiesta has individual coils,we dont know the year or engine size

It doesn't really matter whether it's a single coil or 4, the issues that can cause a failure are still the same.

One thing I would ask OP though, is whether this car has a habit of blowing bulbs......... Because a failure of the alternator voltage regulator would also give rise to odd electrical failures such of ignition coils.

thescouselander

The wife's car had the same problem which I sorted myself but as it happened the ECU incorrectly reported which cylinder was misfiring. Could be that the wrong coil pack has been replaced.