¿Cuando cambiar cables de bujías?

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In this article you will see what are the procedures to measure spark plug wires and know when they are damaged.

When changing spark plug wires

Usually this is one of the processes with more myths within the automotive mechanics. And it is that moment it is advisable to make the change of spark plug wires. Many do so every two spark plug changes or even each time they change spark plugs, they also change the spark plugs. That is why in this article I clarify a little when you should do the cable change so that you do not lose money by doing it prematurely or damaging the coil by doing it too late.

How to make the spark plug wires revision?

The revision or the control of spark plug wires I recommend it every 20 thousand kilometers, and the procedure is as follows:

1.- The first thing is to check that there are no cracks or cuts.

This occurs when there are roses from the cable with another or with a fixed metal part. The rubbing produces a cut that weakens the insulation of the cable, making it susceptible to leakage current or radio frequency that can be heard on the radio.

2.- Roasted cable, or quartered insulation.

Sign of aging of the insulator by high temperature. It is important to choose the correct cable for our engine.

3.- Check the condition of the cable terminals, which are not loose or broken.

4.- The lining of the terminals. There should be no signs of cracks, cracks or dirt. A dirty insulation causes a current leak.

cables de bujia chery a3

5.- Revision of the internal resistance of the cable with a multimeter with ohmmeter function.

The cables have an internal resistance that motivates in a part that the spark flows to the correct cylinder (DIS system) and to reduce the electrical noise of Radio frequency that is produced by the high voltage generated.


The internal resistance of a normal cable made of fiberglass and carbon is at 20,000 ohms per meter. This is a general rule, it is not an exact measurement.

To measure the resistance of the cable we use the multimeter and place it in ohms function, and we adjust the measurement scale in 20k ohms.

And we measure the cable as indicated in the following figure:

medir cable de bujia con multimetro

In this case, this cable is giving us a resistance of 5.56 k ohms or what is the same of 5.560 ohms. For a cable of length of 30cm. Which is normal.

Now, how much must be above, and how much below the general measurement?

It is possible to reach 10% below and 10% above.

Returning to the previous exercise, since we have a 30cm cable, our standardized resistance would be 20k ohms multiplied by 0.3, which gives us 6k ohms. The value that the ohmmeter gave us was 5.56 k ohm. We go by the measure below that would be 6 k - 10% which is 5.4 k ohms (6 - 6x0.1). So our cable is between normal conditions.


A summary of the process would be:

Measure the cable length in centimeters and write it down as variable L.

Rcm = (L / 100) x 20,000 ohms.

Rcmb = Rcm x 0.9

Rcma = Rcm x 1.1

Measure the resistance with the ohmmeter and write it down as variable Rm and verify that:

Rcmb> = Rm (resistance with the ohmmeter) <= Rcma

Conclusions to finalize.

Do not change the spark plug wires without first checking them, a wire pass all the tests described above is as efficient as one just removed from the box.

So do not waste money unnecessarily and be friendly with the environment. Produce waste, deteriorate our planet and exhaust the few finite resources we have.

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Written by:

Chica Mecánica.



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    ¿Cuando cambiar cables de bujías?

    ¿Cuando cambiar cables de bujías?

    In this article you will see what are the procedures to measure spark plug wires and know when they are damaged.

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