GDI injector testing is a far cry from standard port / PFI injector testing. GDI systems have various ways to trigger their injectors and do so at varying pressures. In other words, the varying pressure at the rails varies on demand. By definition, this means the electrical conditions will be varying as well. On a standard PFI system, the pressure remains the same at a steady 35psi – 60psi depending on the system. Nominal PFI injectors draw about 900 milli Amps where GDI Injectors use a Peak-and-Hold Triggering scheme much like the older Throttle Body Injectors. The biggest difference is the voltage and current values employed. GDI internal resistance ranges between 2.6 to 16.3 Ohms, depending on the application. Next, we will explain how GDI Injectors are triggered and how we test them.
Testing a GDI Injector
The analysis of the waveform of the injectors allows us to read how the injector is operating through an oscilloscope. Each Injector’s current waveform has a few points of interest.
One is the injector turn-on point. This turn-on point can go as high as 12 amps. This all depends on fuel demands of the particular engine conditions. The turn on current value will change according to demand. You also need to remember that a GDI open event is much faster than a standard port injection at about 0.04 to 5 milli seconds. Standard PFI has an injector lag time of around .5 to 15 (or higher) milli seconds.
Two is the first stage of the hold current. The idea behind Peak-and-Hold is to supply a high current to quickly activate or open the injector needle. Being that GDI pressures are A LOT higher, you need a lot more current to open, hence the high 12 Amp value. Once it is open, in order to protect the internal coil, the current is reduced down by internal ECM resistor to about 5 Amps.This allows the injector to stay open to the exact same aperture as before or during the 12 Amp current spike, but with less heat.
Three is the second stage in the hold current which is set at about 2.5 Amps. Not all GDI systems have this second hold stage. If they do, it is there to further protect it from heat damage. If available, it is deployed when the injector opening reaches the higher values, or above 3.5 milli seconds.
Properly Testing a GDI Injector
Testing a GDI Injector PROPERLY is no easy mater due to the fact that their operating conditions of of current voltage and pressure are ALWAYS changing. By running an injector in it’s actual conditions is the ONLY way to properly test the condition of the injector. An electrical and pressure “stress test” is required to get the injector ready for testing. Injectors do not fail when initially tested, they fail under “heat”, which can not be replicated without running under the operating conditions.
Companies using a standard port injection machine 100% absolutely CAN NOT do this. Because they can’t, they claim they can see the spray pattern better at low pressures and at static flow. THIS IS FALSE. If you were in the injector business and couldn’t test under actual operating conditions, would you come up with a believable “Excuse” (We will call it), or would you just miss out on all that business? Unfortunately many many places decide to tell their customers this “Excuse”.
You can have your GDI injectors properly tested at Injector-Rehab HERE.