Intermittent electrical problems can be challenging and time consuming. The PDA Lab Scope is always in record mode and the recording can be reviewed and saved so that the hard to find intermittent problem can be verified. Figure 1 shows a convenient way to access the fuel injector signal on a GM CPI fuel injector. The fuel injector circuit is back probed for the voltage signal and the current signal is accessed from the same wire with the milliamp current probe. This van had an intermittent loss of power between 2000 and 2500 RPM while accelerating.
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Figures 2 through 8 are samples taken from a 50-screen file that was recorded during a test drive. Figure 2 shows a normal current and voltage signal the top signal is current flow. Figures 3 through 7 show an intermittent interruption in the current flow to the injector. This 4.3 liter engine has only one electronic injector that supplies fuel to six mechanical nozzles. A loose terminal at the fuel injector caused this intermittent problem. The engine vibration at a certain RPM range caused the injector circuit to open and reduce the required volume of fuel delivery. The low and erratic current signal clearly shows the open circuit to the injector.
