1. What is a Dwell Tach Tester?

Before we delve into the details of using a dwell tach tester, let's start by understanding what it is. A dwell tach tester, also known as a tach-dwell meter, is a diagnostic tool used to measure the ignition dwell angle and engine RPM (Revolutions Per Minute) of a vehicle's distributor-type ignition system. This measurement is crucial as it directly affects the ignition coil's performance, which, in turn, influences the engine's overall efficiency.

2. Safety Precautions

Like any automotive tool, it is essential to prioritize safety when using a dwell tach tester. Before attempting to use the tool, ensure that the engine is turned off, and the key is removed from the ignition. Always wear appropriate safety gear, such as gloves and safety goggles, to protect yourself from any potential accidents during the testing process.

3. Identifying the Dwell Tach Tester

Most modern dwell tach testers are handheld devices with an analog or digital display. The tool typically has two leads: one connects to the positive terminal of the ignition coil, and the other attaches to the negative terminal or a suitable ground on the engine.

4. Connecting the Dwell Tach Tester

To begin the testing process, follow these steps:

4.1 Locate the Ignition Coil

Identify the ignition coil in your vehicle's engine bay. It is usually a cylindrical component with multiple wires coming out of it.

4.2 Attach the Leads

Take the red lead of the dwell tach tester and connect it to the positive terminal of the ignition coil. Next, take the black lead and attach it to the negative terminal of the coil or any suitable engine ground.

4.3 Switch on the Dwell Tach Tester

Turn on the dwell tach tester and ensure that the selector switch is set to the appropriate settings for your engine. Some testers have a manual switch, while others may automatically detect the engine type.

5. Checking the Dwell Angle

The dwell angle refers to the number of degrees the points in the distributor remain closed during each cycle. Follow these steps to check the dwell angle:

5.1 Crank the Engine

With the dwell tach tester powered on and connected, crank the engine. The tester will display the dwell angle measurement on its screen.

5.2 Ideal Dwell Angle

Consult your vehicle's service manual to find the ideal dwell angle for your specific make and model. In general, most older vehicles with contact point ignition systems require a dwell angle of around 30 to 45 degrees.

5.3 Adjusting the Dwell Angle

If the measured dwell angle deviates from the ideal range, adjustments might be necessary. To adjust the dwell angle, you will need to access the distributor and manually adjust the points' gap.

6. Measuring Engine RPM

Apart from checking the dwell angle, a dwell tach tester can also measure engine RPM. Here's how to do it:

6.1 Locate the RPM Source

Identify the engine's RPM source, which is usually located near the engine's crankshaft or the distributor.

6.2 Connect the Leads

Take the red lead of the dwell tach tester and connect it to the RPM source. The black lead should still be connected to the negative terminal or a suitable ground.

6.3 Read the RPM

Start the engine and observe the dwell tach tester. It will display the engine RPM on the screen.

7. Conclusion

Using a dwell tach tester is a valuable skill for any automotive enthusiast or mechanic. By accurately measuring the dwell angle and engine RPM, you can diagnose and fine-tune the ignition system, ensuring optimal engine performance. Remember always to prioritize safety and refer to your vehicle's service manual for specific dwell angle and RPM recommendations.