Spark plugs are responsible for producing the spark that allows the combustion of a gasoline engine. If they are in poor condition, it will work abnormally and may generate vibrations or even turn off. We teach you how to check spark plugs to find out if they are the problem with your car.
Furthermore, taking advantage of the inspection, you will be able to know the general condition of your car's engine. Because, depending on how the spark plugs are, they can be detect other faults of varying severity.
Spark plug check
The first thing we must do is a visual check of the state of the spark plugs. That is, they do not have breaks in the insulation, excessive electrode wear o dirt accumulated. If they have a broken insulator or excessive electrode wear, it is necessary to change them. On the contrary, if they are dirty, it may be enough to clean them.
The next step is to go beyond what meets the eye. Even if they are not broken or worn, there is another important test that should always be done: check the spark plugs with a multimeter. It is a simple operation that only requires a cheap tool. In the following video you can see how to use it and how to check the spark plugs:
We also put the steps in writing in case it is more comfortable for you. The first thing is to check the Resistance between terminal and center electrode, which in the case of spark plugs must be between 3.000 and 7.500 Ohms.
- Let's set up the multimeter for it: put the multimeter on Endurance mode, which is indicated by the letter omega (Ω) and with the measurement scale immediately above what we expect. In the video it is 20.000 Ω, but in others it can be 10.000 Ω, 40.000 Ω, etc.
- Plug the test leads into the correct ports on the multimeter: black wire into COM port y red wire where the indicated letter omega (Ω).
- Place the test leads: one in the terminal of the spark plug and the other in the center electrode (the tip that is under the ground electrode that curves over it)
- If you give a value above or below of 3.000 Ω and 7.500 Ω, the spark plug is bad and you have to change it.
The second check is see if its parts are properly insulated, otherwise it wouldn't work:
- To do this, set the multimeter to Continuity mode, which is indicated by the diode symbol, which is an arrow headed by a vertical line. It is also indicated with a kind of speaker.
- plug the test leads on the same ports of the multimeter that when measuring resistance. That is, black cable to the COM port and red cable where the letter omega (Ω) is.
- Place a test tip on the thread spark plug and another in the terminal. If the multimeter doesn't beep, it's well insulated there.
- Now place a probe in the central body spark plug and the other in the terminal. If it's ok, it won't beep either.
The condition of the spark plugs indicates other faults
Now that we have inspected and checked the spark plugs, we can know the condition of the engine carefully analyzing the condition of the spark plugs:
- If the spark plugs have a light brown hue on center electrode insulator and the electrodes do not have excessive wear, the motor works correctly.
- Carbon deposits on spark plugs: May be due to a rich mix or lack of compression. If it happens only in one spark plug, it may be a defect in the high voltage cable.
- Great deal of carbon deposits moistened in oil: It means that there is a lack of sealing in the engine, due to wear of the cylinders or segments.
- White hue and electrodes with excessive erosion: It means that the engine has been working at temperatures higher than usual. This can be due to various causes, such as excess ignition advance or air intakes in the intake manifold, Among others.
- Spark plug with melted electrodes: it may be that this cylinder has auto start. In this case, it is necessary to analyze what it is due to, since if we continue driving with the car we can suffer a serious breakdown.
- Cracked spark plug insulators: May be due to detonation, which needs to be checked. If they also have bumps, it may be to an object that is in the cylinder.
- Easily removable abundant deposits: It can be due to fuel detergent additives and also due to the use a spark plug of a lower thermal degree to the appropriate one.
And what if the plugs are good?
If we notice that our vehicle fails or has irregularities in the operation of the engine, one of the reasons may be the spark plugs. So it doesn't hurt check its status. However, they are not the only parts that can fail and give similar symptoms (difficulty starting, vibrations and engine shutdown).
If symptom are vibes, the most common elements that can fail are injectors, ignition coils or the silentblocks. The first, because they are dirty or partially clogged and the fuel does not reach one or several cylinders well. The second, because they are broken and cannot dampen the vibrations of the engine.
If the symptom is difficulties starting, most common problems are car battery or alternator that does not load it, the starter and fuel pump. We recommend the article: My car won't start: how to know what's wrong and fix it.
In conclusion, if what happens to your car is that it turns off by itself, the problems can be many. For example, an electrical system with a battery or alternator in very poor condition, or with loose or frayed cables that generate excess resistance to the flow of electricity (Ω). Also the crankshaft position sensor (CKP sensor), which sends a signal to the switchboard to know the rotation of the motor. If it doesn't work, the motor will die. Another example is, again, a bad fuel pump or other problems in the electronic injection system car.