Vince Manship from Group Training Academy by AVI discusses voltage drop testing using a scope, specifically his Launch X431 Throttle 3. He emphasizes that the scope type doesn’t matter, but proper technique is crucial, especially with increasing corrosion-related failures in older cars.

Manship explains that for output devices like fuel injectors, it’s best to connect the scope close to the component. Measuring at the computer might miss problems in the wiring or connectors between the computer and the device. He demonstrates how damaged connectors can lead to resistance issues that are only visible when testing directly at the component, not just back-probing.

He recommends using specialized leads that fit the connector terminals, allowing for drag tests to check terminal tension.

Setting up a demonstration with an injector and a 22-ohm resistor, Manship illustrates that a scope measures what’s between its leads. Initially, with no current flowing, the voltage remains constant across the resistor because resistors only resist current, not voltage.

When the injector is activated, creating current flow, a voltage drop is observed. Using the scope’s cursors, he measures a 6-volt drop across the 22-ohm resistor, confirming that voltage is being consumed due to resistance. This problem was only visible when testing after the resistor (i.e., within the connector, simulating the actual fault location), not before it. This highlights the importance of correct scope hookup to accurately identify voltage drops.