Recently I found my Ford Fiesta was behaving erratically and missing. My first step was to clean the plugs and check the gaps. The problem seemed to go away, but was back within a week. However suddenly my exhaust started blowing and I thought it may have been erratic due to this. When I took my car to have the exhaust replaced, they suggested it was missing. Even though I had only cleaned the spark plugs two weeks ago they were now black, I was concerned about the engine compression, but know this is now not the case.
Rather than have the garage fix the problem, I decided to fault find myself, it helps that I was trained as a Process Control engineer. The first thing I did was change the spark plugs, you will find these under the cover you can see in the first picture. Remove the six screws and the oil cap and put safely in the cover.
***Always replace the oil cap before starting the engine***
Get the correct spark plug remover. Set the spark plug gap to 1.3 on a 1.25 litre Ford Fiesta. If this doesn’t resolve the issue, the next thing to look at is the plug leads.
You can change all the plug leads or find a spare and substitute one at a time and see if this cures the issue. I changed all mine at once, but the quality of the replacement leads was that bad, I had to return the plug leads and source a new set.
I did find a faulty plug lead, but the erratic missing was still happening.
Finally I replaced the coil pack and the issue went away. The hardest part of replacing a coil pack, was undoing the 4 screws that hold it on the chassis. I bought the correct star type allen keys, but two of the screw heads threaded. I had to break the coil spring body and remove two of the screws with mole grips. I then created screw slots in the screws with a hacksaw.
The plug leads were marked on my new coil pack,but you may wish to mark the plug leads before removing. There is one electrical connector on the side of the coil pack, which can be prised off with a screw driver, make sure you put it back on the right way.
The spark plugs cost £9, plug leads £12 and Coil pack £32. The coil pack is the electronic ignition, replacing the points that you used to have to manually set on older cars. I recommend purchasing replacement parts here www.eurocarparts.com
Remember to put the oil cap back on before starting the engine.
I can’t believe the difference in the economy of my car.
All the best