The Sunday News
My car shakes a lot when idling, runs very rough and using too much fuel . . .
IT sounds a lot like your car has a serious misfire. A misfire simply means that one or more cylinders are not firing correctly or not firing at all. Some of the first things you will notice with a misfiring engine are significant loss of power, poor fuel economy and the heavy shaking when the car is idling.
There are many causes of a misfire but it’s usually ignition related. You will need to check your spark plugs, distributor or ignition coils or distributor cap for cracks or carbon build up and HT leads for damages. In some cases it can also be a vacuum leak so you need to check for broken pipes as well.
Under normal circumstances, spark plugs do not need high maintenance. It is wise however, to check every once in a while to see that they are still in good shape and are clean.
Carbon build up on spark plugs can create an insulation that can make it impossible for ignition especially where the engine is also burning some oil or contaminated fuel.
Oil leaks into the cylinder perhaps through worn valve guides, seals and piston rings can eventually coat the plug electrode with oil deposits and make it harder to start the car and cause misfire.
Occasionally it is worth the while to check plugs to make sure they are clean. Repairing the leak however, is the best thing to do when you see oily residues on spark plugs. Oily residues on spark plugs are a sign that something is amiss.
Naturally, you ought to change plugs at specified intervals as the user manual directs but I know most people do not have the luxury of having user manuals in a language they can actually understand so I hope this helps. When your car misfires, it can be bad or worn out plugs.
Before even calling the mechanic, you can pull some DIY stunts and you might just be lucky to find a bad plug.
There are plenty other causes of a misfire like broken HT Leads, faulty coil-packs, distributors and sometimes water where it is not supposed to be. Spark plugs may always be the first port of call when checking for a misfire.
Reduced power and more fuel consumption can also be traced back to worn plugs; anything that causes incomplete combustion also paves way for higher fuel consumption.
The spark from the spark plug makes the difference whether your car is going to start or not, whether it is going to perform efficiently or not.
Difficulties when starting the engine may also point to faulty or dirty spark plugs. If your engine cranks a lot before running you may need to check the condition of the plugs.
The quickest way to check for the problematic cylinder is to remove HT leads one by one when the engine is running.
The HT lead that you remove and makes no difference whatsoever to the engine is the problematic one. When I say “difference” I mean if you remove one HT lead that is working, the shaking should get worse and you should notice a change in the RPMs, if there’s no change at all when HT leads are pulled then something is amiss with that cylinder.
Modern cars have computers running the engine and if you have an engine check light on your instrument cluster while the car is running then you need to check the car for errors. This is done by way of plugging in a diagnostic tool.
Older cars are quite easy to deal with. Everything is out in the open. Newer cars however, have all kinds of funny gadgetry going on under the hood but it’s not usually anything impossible for the DIY enthusiast. The condition of the plug should simply be the same way they were when they were new.
If they are clogged it’s a telltale sign for something not right. If the plug is clogged with black soot, it may indicate that the car is running on a too rich a fuel mixture.
If the plug is oily, it also means a leak somewhere. Cleaning them can do the trick for smoother performance.
Whenever you find damaged plugs, always replace and when time is due, replace all of them at once to avoid major problems.
The engine does not need foreign particles to fall into the combustion chamber. Whenever you check plugs you would want to make sure that the area around the plughole is clean, if not, clean it first.
Any debris falling into the combustion chamber may cause all kinds of problems for you. A small brush with a cleaning agent can do the trick for the spark plug.
Ideally, you would want to use a quick drying liquid like injector cleaner or carb cleaner to clean the plugs. Petrol works fine as well but remember its highly flammable.
When removing or reinstalling plugs be careful to line up the threads correctly, be gentle.
Do not force the plug or you will cross-thread, then you will know the definition of stress.
So to answer your question misfire can be caused by a bad plug, HT lead ignition coil, distributor or vacuum leaks.
Check these simple things first and if it doesn’t solve your issue, then consult a professional.
Do you have an issue you need help with?
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This is only an advisory column, get professional help every time you have car problems.
