Turbo models have low impedance injectors (2-3 ohms), and include a resistor pack in the electrical system. Non-turbo models (including the Spyder 2.4L) have high impedance injectors (13-16 ohms) and do not have a resistor pack.
The resistor pack is installed to ‘fool’ your ECU into thinking it is driving high impedance injectors. Vehicles that have low impedance injectors AND resistor packs have ECUs that use a saturated signal to operate low impedance injectors.
If you are unsure because your vehicle is modified, you can measure the resistance across the two electrical terminals of the injector. If the resistance is between 1.5 and 4.0 Ohm you have low impedance injectors. If the resistance is between 8 and 16 Ohm you have high impedance injectors.
Low impedance injectors are designed to be driven by peak and hold signals. Most of the OE manufacturers that produced cars with low-Z injectors chose a “workaround” to using the low-Z injectors since it wasn’t cost effective to produce an ECU with the necessary circuitry and injector drivers to produce these P&H signals for the few high performance cars that needed it.
The way they solved the problem was to add a resistor box into the fuel injector harness, thereby increasing the resistance in the circuit to the higher value needed to prevent the ECU injector drivers from overheating due to excessive current draw. (e.g. low-Z injector resistance is 3.0 Ohm, plus in-line resistor of 7.5 Ohm, making a total resistance of 10.5 Ohm, which is safe for the ECU).
For more information about Injectors, visit the Fuel Injector Clinic FAQ page
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