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as the "peak" time, referring to the fact that current flow is allowed to "peak" (to open the injector). Once the injector pintle is open, the amp flow is considerably reduced for the rest of the pulse duration to protect the injector from overheating. This is okay because very little amperage is needed to hold the injector open, typically in the area of one amp or less. Some manufacturers refer to this as the "hold" time, meaning that just enough current is allowed through the circuit to "hold" the already-open injector open. There are a couple methods of reducing the current. The most common trims back the available voltage for the circuit, similar to turning down a light at home with a dimmer. The other method involves repeatedly cycling the circuit ON- OFF. It does this so fast that the magnetic field never collapses and the pintle stays open, but the current is still significantly reduced. See the right side of Fig. 1 for an illustration. The advantage to the current controlled driver circuit is the short time period from when the driver transistor goes ON to when the injector actually opens. This is a function of the speed with which current flow reaches its peak due to the low circuit resistance. Also, the injector closes faster when the driver turns OFF because of the lower holding current. NOTE: Never apply battery voltage directly across a low resistance injector. This will cause injector damage from solenoid coil overheating. THE TWO WAYS INJECTOR CIRCUITS ARE WIRED Like other circuits, injector circuits can be wired in one of two fundamental directions. The first method is to steadily power the injectors and have the computer driver switch the ground side of the circuit. Conversely, the injectors can be steadily grounded while the driver switches the power side of the circuit. There is no performance benefit to either method. Voltage controlled and current controlled drivers have been successfully implemented both ways. However, 95% percent of the systems are wired so the driver controls the ground side of the circuit. Only a handful of systems use the drivers on the power side of the circuit. Some examples of the latter are the 1970’s Cadillac EFI system, early Jeep 4.0 EFI (Renix system), and Chrysler 1984-87 TBI. INTERPRETING INJECTOR WAVEFORMS INTERPRETING A VOLTAGE CONTROLLED PATTERN NOTE: Voltage controlled drivers are also known as "Saturated Switch" drivers. They typically require injector circuits with a total leg resistance of 12 ohms or more. NOTE: This example is based on a constant power/switched ground circuit. * See Fig. 2 for pattern that the following text describes. Point "A" is where system voltage is supplied to the injector. A good hot run voltage is usually 13.5 or more volts. This point, commonly known as open circuit voltage, is critical because the injector will not get sufficient current saturation if there is a voltage shortfall. To obtain a good look at this precise point, you |