Testing a Distributor: A Complete Step-by-Step Guide

Testing a distributor, which is the part of your vehicle that passes an electric voltage to the spark plugs, can be a slightly complex procedure for those who need to become more familiarized with the mechanisms of a car. Regardless, the most essential part of this process would be appropriate instructions and the right tools, and you can finally be sure of getting the good results.

Testing a Distributor

Before you decide whether to check your distributor, you must know all the foolproof methods of checking if something is truly wrong with it. You can do this in a fool-proof way by reading the guide below, and you can follow the given instructions to test the distributor effectively!

How Can You Test a Distributor With a Multimeter?

You can test a distributor with a multimeter by removing the cap and the rotor. Then you will need to check the reading that appears and ensure it is normal. If it is not, you will know something needs to be fixed with the distributor.

1. Removing the Cap and Rotor

Suppose you decide to test your vehicle’s distributor using a digital multimeter. In that instance, you will first need to understand the mentioned tool. You will then have to head over to the distributor and remove both the cap and the rotor, ensuring you are not rash or careless with it.

Once you have removed both the rotor and the distributor cap, you must locate the terminals on the coil, both the positive and the negative. Once located, you need to connect the multimeter to them.

2. Checking the Reading

After you have linked the multimeter to the terminals accordingly, you must set it to the OHMS mode. Once this is done, you must properly look at the reading and assess it thoroughly.

Checking Car Reading

Suppose you need to familiarize yourself with how a multimeter works. In that instance, you should remember that the ideal range of resistance incoming from the suppressions connections is anywhere between 600 to 1400 ohms.

3. Checking Whether It Is in Normal Range

Once you check the reading that is showing up on the multimeter, you will need to inspect whether or not it is in the normal range. If it is in the normal range – between 600 to 1400 ohms – then you can rest assured that the distributor is working just as it should.

However, if you see that the numbers showing up are not in the normal range, you will have to replace the component, which would mean it is faulty. The next step you should follow is check the pick-up coil connected to the distributor. Once again, you must link the multimeter to the coil terminals and turn it to the OHMS mode.

After this is all finished, you will need to examine the reading that will show up closely. If you see that everything is well within the normal range, there is no need for concern, as this indicates that the coil is in optimal condition. If this is not the case, the coil is faulty and needs to be replaced.

How Can You Test a Distributor Cap and Rotor?

You can test a distributor cap and rotor by first removing the cap and checking its inside for any faults. As for the rotor, you have to remove it as well and look inside at the wiring. Also, check if there is a gap between these components or not.

1. Testing the Cap

If you need to test the components of the distributor, namely the rotor and the cap, you can do this with ease as long as you stick to the instructions. First, you must remove the distributor cap properly and then turn it over to check the inside.

If you find it clean and undamaged, you may use a wire brush to scrub off any debris accumulated over time. However, if the issue persists, replace the distributor cap with a new one to ensure the smooth functioning of your engine.

2. Testing the Rotor

Testing the rotor in your vehicle’s distributor system is essential in maintaining your engine’s functionality. To perform this task, remove the rotor and hold it in a well-lit area. Here, you should have a clear view of the contacts on the rotor, and also look for the wires in the distributor cap.

Testing Car Rotor

Look for a visible gap between these components, as it is crucial to the proper functioning of your engine. If this gap is too large, keep in mind that it can cause many issues, from erratic sparks to no sparks.

3. Cleaning the Rotor

It is time to clean the rotor if you notice any signs of wearing or damage, such as debris buildup or corrosion. You can use a wire brush here to remove accumulated debris, giving it a thorough clean. However, if the issue persists, replacing the rotor may be necessary to ensure your engine runs at its best.

4. Testing the Vacuum Advance Unit

The vacuum advance unit in your vehicle plays a crucial role in ensuring efficient fuel consumption and optimal engine performance. As part of your vehicle maintenance, it is essential to inspect this unit regularly. Begin by removing it and conducting a thorough inspection for any visible cracks, leaks, or other forms of damage.

Suppose the unit appears to be clean and in good condition. In that case, try using a wire brush to remove any debris or even dirt that may have accumulated. However, if the issue persists, replacing the vacuum advance unit may be necessary to ensure your engine runs efficiently and effectively.

How Can You Replace a Distributor After Testing?

You can replace a distributor after testing by removing the old components and the distributor. You will now need to attach the new components and reconnect the wires. Once everything is ready, you can now test whether it is working or not.

1. Removing Components

To carry out this step effectively, you need to start by removing the old distributor cap and rotor carefully. Once these components are out, you can proceed to the next step: disconnecting the vacuum advance unit.

To do this, take the necessary precautions to avoid damaging the unit and ensure you have the correct tools. Once disconnected, carefully remove the unit from the distributor system.

2. Removing the Distributor

Next, you can proceed by disconnecting the wires leading to the distributor, ensuring you keep track of their positions to make reinstallation easier. Once disconnected, use the appropriate tools to unscrew the distributor from the engine block carefully.

3. Attaching the New Components

As for this next step, you will need to start by attaching the new rotor to the distributor’s shaft, ensuring it fits snugly. Next, attach the new distributor cap and screw it into place, ensuring you tighten the screws appropriately. Following the manufacturer’s instructions when installing the new distributor cap is essential to ensure proper fit and function.

Attaching New Components to Car

Finally, all you need to do is reconnect the vacuum advance unit and screw it back into place, ensuring you connect it correctly to avoid any potential damage. After completing this process, check that all connections are secure and everything is in its right place.

4. Reconnecting Wires

After installing a new distributor, reconnecting all wires leading to the distributor is essential to ensure the engine functions correctly. Start by checking the wires for any signs of wearing or damage, and replace them if necessary.

Then, connect the wires to the distributor, ensuring they are connected to the correct terminals. After making the necessary connections, use the appropriate tools to screw the distributor into the engine block.

5. Checking the Results

Once you have completed the process of installing and reconnecting the distributor, starting the engine is the next crucial step. After starting the engine, check if the problem that prompted you to replace the distributor has been resolved. If the problem persists, you must adjust the distributor’s timing.

How Can You Adjust the Timing of the Distributor After Testing?

You can adjust the timing of the distributor after testing by first disconnecting the spark plug wires and then attaching the relevant wires to the timing mark that appears on the crankshaft pulley. When you are finished, make sure to also check the results.

1. Disconnecting Spark Plug Wiring

The distributor’s position relative to the engine determines when the spark plugs fire, and it needs to be accurately set to ensure the engine runs smoothly and efficiently.

Disconnecting Spark Plug Wiring

To begin the process, you must warm up the engine to its operating temperature and connect a timing light to the number one spark plug wire.

2. Locating and Attaching the Timing Mark

Point the timing light at the mark on the crankshaft pulley, and it will illuminate the mark’s location. It’s essential to ensure that the timing marks are aligned correctly with the manufacturer’s specifications to prevent any potential damage to the engine.

If the timing is seen to be off, you can use a wrench and a distributor adjustment tool to adjust the distributor’s position until the timing is correct.

3. Checking the Results

When starting the engine and letting it idle, make sure that all other accessories are turned off to get an accurate reading. Additionally, if the timing is not within the manufacturer’s recommended range, you must adjust the distributor accordingly.

Turn off the engine, loosen the distributor bolt with a wrench, and then use the distributor adjustment tool to turn the distributor in either direction slightly. Re-tighten the distributor bolt and start the engine again to check the timing with the timing light.


Every car owner needs to know the proper ways of keeping their vehicle in top condition and essentially maintained so that it can operate smoothly, and the distributor’s condition has a great impact on the vehicle’s overall performance. It is a necessity to know all the right ways to test it – and thus keep it maintained – as you will have seen in

the article above, and can check again with the following points:

  • To identify an issue with the distributor, check the rotor and cap, which may have worn out, and the vacuum advance unit.
  • A worn-out rotor and cap can cause a vehicle’s overall performance to deteriorate and misfire, which could lead to accidents on the road.
  • If there is no issue with the rotor and cap, the problem might be with the vacuum advance unit that maintains engine efficiency.
  • Test the distributor with your multimeter by checking the coil terminal resistance (600-1400 ohms) after removing the cap and rotor.
  • To test the distributor cap and rotor, remove them and check inside for faults and look closely at the wiring and gap.

While the techniques in the article are sure to help you learn the process of checking whether anything is wrong with the car distributor, it might be crucial to take the car to a mechanic if you still need to be more confident in doing it yourself. However, since all the steps and instructions provided in this post have been made especially easy to follow, there will be no need to go to a mechanic as you should be able to handle it yourself!

5/5 - (15 votes)
Ran When Parked