How to Test Oil Filled Ignition Coil | Step-by-Step Guide

Oil-filled ignition coils are generally 12V ignitions coils, installed in the engines of the vehicles. They serve the purpose of the transformer. They take voltage from the battery and build it up to several volts that create a spark in the spark plug. This is how fuel cylinders burn fuel inside it and the engine starts.

If a spark plug or its wiring is faulty, there is a chance that it creates unbalanced voltages from the ignition coil. It will lead to the burning of the coil.

There are various ways to check the status of an oil-filled ignition coil. Previously in this article, we have studied some ways to check the status of the coil pack without using any tool. However, in this article, we will see how to test the status of the ignition coil by using a multimeter as oil filled coil are often difficult to swap inside different cylinders.

If you don’t have the multimeter then you can try this method to test the oil ignition coil.

Testing the oil filled ignition coil using multimeter

In order to check oil filled ignition coils, follow the below mentioned steps:

  1. Before opening the hood of your vehicle, first, wear the safety gloves and glasses that’ll protect you from shocks during the testing process. If you don’t have this equipment, I would advise you to gather them first and then move on to the next step.
  2. Now, locate the ignition coil and do note that it’s located at different locations in all types of vehicles. So, turn off the engine of the vehicle first and open the hood and start searching for the ignition coil.
  3. After locating the ignition coil, take out a wrench and disconnect the battery cable having negative polarity from the engine. It is normally having black in color.
  4. The next step would be to identify the coil wire of the main ignition. You will see it connected to the distributor. After locating it, pull that particularly gently outwards.
  5. Now identify the small grounding wire inside the engine and using a wrench, attach it with the side of the coil wire we identified in the previous step.
  6. Now, it’s time to use the multimeter. Make sure you are using a calibrated and fully functional meter. A wrong multimeter may not lead to a fault diagnosis that would cost you both money and time.
  7. As, we’ve to measure the resistance so, set the functionality of the multimeter to the ohmmeter. Do note the unit while noting down the value.
  8. After setting the multimeter to resistance measurement mode, take its one probe and insert it into the center opening of the main ignition coil that was leading to the distributor. Insert it in such a way that inside of the coil, it must touch its metallic terminal.
  9. After making the connection, check the readings on the screen of a multimeter. If it is showing the value of resistance in between 6000 to 15000 Ohms then the coil is ok. It means we are good to go. But if the value is different than the above-mentioned range, there is a fault in the secondary winding.
  10. Now again touch one probe of the multimeter with the ground terminal. However, this time connect another probe to the terminal bolt which is present at the other side of the coil.
  11. After setting the connection, check again the readings on the meter. If the value of resistance between 0.4 to 2 ohms, then there is no issue in the coil. But, if the value is not in this range then the primary winding of the coil is having some problem.
  12. Do note to test both the primary and secondary coils. After identifying which side of the oil filled ignition coil is having a problem, remove the coil. Now is the time to replace it with the new one.


Can an ignition coil work intermittently?

Yes, ignition coils can work intermittently which means they seem to be perfectly fine when tested by a mechanic in his shop and will pass all tests. But, while traveling when they have to face fluctuating loads, the coil won’t fulfill its function and cause serious ignition issues inside the engine. It’s one of the most difficult faults to diagnose.

Can ignition coil damage spark plug?

The ignition coil can’t damage the spark plug directly, but it can overheat them. That ultimately leads to indirect issues causing an imbalance in the ignition process. So, if you feel the ignition coil is faulty, try to replace it with the new one on time to avoid any serious damage to the engine.

Final Thoughts!

This is how you can test the oil filled ignition coil using the multimeter. The process is pretty simple and you won’t need help from any professional. However, if you see fluctuating readings while measuring the resistance for either secondary or primary coil, hire a mechanic. He’ll do a thorough inspection of your vehicle.

Also, if your engine is not starting at all and readings are perfectly fine while testing the ignition coils, there might be some other issues that can be diagnosed by a professional mechanic!

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