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NOVEMBER 2021 AFTERMARKET 21 September and October issues of Aftermarket), so we will begin with a simple saturated 15-ohm injector circuit. (See Fig.1). You will observe that the current increase takes a slightly curved profile with a distinctive kink, this is the point when sufficient current flow allows the pintle to lift against the spring and fuel pressure. So, it was possible to predict sticking or late opening due to high fuel pressure without removal or injector bench testing, which was in its infancy then. Previously the back EMF, normally around 80v, would indicate sufficient current and induction properties. Focusing on current analysis also confirms good voltage and ground paths. Switching will be found on power or ground and in some cases current flow may toggle within the PCM. Power switching and pulse width modulation (PWM) provides an initial high current peak with a reduced current period, allowing a much more accurate feedback sequential fuel trim. Intention Next, please refer to Fig.2, a PICO image as before, this time showing VAG power switched injector control. Given the range and variety in current clamps the world is our oyster when it comes to future application. When developing diagnostic process, we must first understand the limitations with test options and the various types of component control. Having evolved from a simple saturated (on off) to PWM (on off variable period and frequency) to micro current and SENT (single edge nibble transmission) and data and diagnostics transmit only, our ability to diagnose components is being driven entirely to the serial platform. This is of course exactly what the VM intends. How then might we use current measurement for control and response purposes? The control or command may be analogue, digital, duty, PWM, or binary format. However, all components that require movement or heat as a function require current flow and as such can be measured anywhere in the power or ground circuit. Idle With this in mind, let’s look at a very simple idle air bypass valve. My intention here is to emphasise the importance of having the correct device. I will also show a similar example from a VAG swirl flap control. Please refer to Fig.3; Ford idle air valve current flow. Note the inaccuracy in current value despite using similar devices. Now, look at Fig.4. Despite an obvious simple digital control signal, the current flow appears linear at 100mv = 1amp. Not possible, now compare the event with a more sensitive current clamp. Please refer to Fig.5. Increase To conclude my topic, I am sure many of your techs have replaced throttle body control modules, turbo vane control modules and EGR and swirl flap control motors. If so, I suggest checking the current path and feedback movement sensors. There should be an obvious synergy between current flow and movement, where a mechanical restriction will cause the PCM to increase the current supply. If this becomes excessive there will be a hard DTC, however this often leads to premature drive motor failure. www.aftermarketonline.net Fig.2 Fig.3 Fig.4 Fig.5