The most common causes of engine misfires

Is your engine misfiring? Having trouble starting the ignition? We identify some common causes.

If your engine is failing to start, misfiring or rattling, there might be several causes, ranging from an easy fix to more complex issues. We find out what they are, and how you can help everything go more smoothly.

Please note, when dealing with electrics, you will need to take your car to a qualified technician. To book your car in for a service at Arnold Clark, click here.

Spark plugs

Have you lost your spark? If there’s no spark, there’s no ignition, so this should be your first port of call. Spark plugs don’t cost much to replace, and they are the most common culprit for engine misfire, so get them checked first.
Faulty plug wires

The spark plugs have wires on them leading to the ignition. If your wires are getting older or just not working as they should, you might notice the following signs: erratic idling, engine misfire, a ‘check engine’ light on the dash, radio interference and decreased fuel mileage. Ignition misfires

Wear and tear on your ignition components might not be obvious at first, but as they deteriorate, you may hear the loud ‘pop’ as the combustion process is interrupted completely. If that happens, step on it and drive to your local service centre.

Fuel injectors

After a while your engine’s fuel injectors may get clogged up and dirty, especially if you often drive short distances, as stopping and starting can accelerate the process. It’s a good idea to check whether this is the case first, but if it is, fuel injector cleaners can easily be added to your tank.

Lean misfire

This is caused by an imbalance in the air/fuel ratio, and may be more noticeable when your engineis idling but may disappear when your engine speed increases. Get your fuel pump and filter checked, as well as your EGR valve and intake gasket.

Worn piston rings

Piston rings help to regulate oil pressure in your engine, and when they get worn, it can cause misplacement of the pistons or the spark will fire at an incorrect part of the combustion cycle. You can tell this is happening if you get a lot of fumes from your exhaust or there’s less power when you accelerate.

Leaking head gasket

Blown a gasket? It’s possible. If there’s a failure between cylinders, compression from one cylinder leaks into another. Lowered compression results in a rough idling engine.

Transmission issue

It might not be a misfire at all…sometimes an erratic performance might be down to your transmission, which could be having trouble shifting up and down. A trained technician can help you diagnose the problem.

Chattering clutch

So you’re driving along quite happily and you get a misfire. Again, the problem might not be in your engine – it could be to do with the overdrive gear or a chattering clutch, which again could be down to other disc-related or pressure plate issues.

Sticking brake pads

If the vehicle jerks or something feels like it’s missing when you start to slow down, it could be due to a number of factors, including rough transmission downshifts, warped rotors or sticking brake pads.

Whatever misfiring problems you’re experiencing, Arnold Clark has 150 Service Centres across the UK who can help you find the cause.