Injector tester with IRF520

I decided to build an injector tester. It will allow the system to inject into measuring cylinders, where differences in the amount of fuel will be visible if an injector does not give the required dose. In this section, we will look at the selected components and in the next section we will show whether the system works or required a change from the original design. The injector tester will use a microcontroller, MOSFET to control the injector coils.

My tester is compatible with GM 55562599 injectors, which appeared in 1.6E Ecotec engines, which were indirect injection. This engine for Chevrolets existed in various power variants, namely 83, 86 and 91 kW with the code designation F16D4, or LDE. The same injectors should also be used by the A16XER engine from Opel 85 kW.

For such an injector assembly, I of course also needed a 55567239 harness, rail 55562597, i.e. an injection rail on which the injectors are mounted and which has a fuel supply from the pump. Since the assembly will not be in the car, I also needed a pump and a filter. I got all these parts through Allegro in Poland for a few bucks. I also bought the injection rail directly with the injectors for 10€, while normally a new injector can cost up to 90€ per piece.

The injection rail also has a valve where you can connect a fuel pressure gauge, it has a Schrader NA 7/16" thread, but I couldn't find it and I don't know if it is compatible with 7/16 UNF threads, probably not... The injectors didn't look that bad after delivery, the nozzles were visible on all of them with a total of 8 holes. So did the €10 cable harness and a pump that will give 3.8 bar operating pressure. Any pump was enough, I found one for old Opels with this pressure, which was used on Ecotec engines of the previous generation, but the technology remained unchanged.

All these components will need to be powered and therefore they will need enough current and a hard source. I therefore used an old ATX 300W power supply from which I can conveniently use the 12V branch (yellow cable) to power the injectors, pump and, if necessary, the 5V branch (red cable) to power the other control electronics. In terms of electronics, I decided to use what the drawer gave. I found a PCB for RFID DOMINATOR 1.0, which remained unused and unmounted, and also a Keywish Arduino Nano. For control, I was looking for a transistor or mosfet that I would use, preferably as a module that would fit directly on the PCB and I would not have to pull the cable from the Arduino and solder them.

I found a module with an IRF520 MOSFET, which has 3 pins, signal, ground and Vcc, and it fit directly into the RFID DOMINATOR 1.0 PCB in the place where the LCD 2004A character display is connected. Although the signal pin does not support PWM, but since we would not use PWM as such here, because we are not controlling power, but continuous opening time, a standard GPIO will suffice. In this case, on the Arduino Nano it was the SDA pin, i.e. pin A4, which (yes, it is analog), but can also be used as a digital output.

It is recommended to use a heat sink for the module when the current exceeds 1A. I therefore used an aluminum finned heat sink 11x5x11 mm, which has 3M tape with a thermally conductive black layer and holds really well. The module is supposed to handle 5A, which is specified for a 10V voltage on the control pin when the MOSFET is fully open. Since the Arduino has a 5V GPIO, we will see in a real test how many A it can handle and whether it will be sufficient for the needs of the injectors, or we will have to reach for another MOSFET. There is also an IRFZ44N in reserve, which is for many times higher power and at 5V has many times higher permeability. However, it will be necessary to make some electronics for it in the form of resistors and the like, which the module already had solved.

So how will it all be connected?
First of all, you need to look into the documentation of this injection system and find out which pole is switched. As we can see in this schematic, the injectors always have 12V voltage present and a ground is switched, which closes the circuit and opens the injector. By default, the injector is open for a few milliseconds (units and low tens), which depends on the load, accelerator pedal position, engine temperature, etc.

So we will switch the ground via the MOSFET and 12V will still be connected to the injectors. The module with IRF520 has, in addition to the aforementioned Vcc GND and SIG terminals, also others, namely terminals with VIN GND (both GNDs are of course connected to the PCB) and also at the output of the module there is a terminal V+ V-. When the transistor is switched on with a HIGH signal, VIN appears on V+ and GND appears on V-. In this case, we will use V-, where we will connect all the injectors that we will control synchronously.

I had to disassemble the wiring harness and cut off the connector. This connector has a total of 5 pins, 5 cables in a 7-pin connector. So 2 positions are unoccupied. Logically, we have constant 12V on one wire and the other 4 cables represent the ground to each injector separately, so that each injector injects separately when it has to at the required time. The color distinction is simple, the red cable is 12V, the other yellow-brown and similar colors are GND.

I blanked the cables and connected them to the WAGO terminals, which connected the grounds, thus synchronizing the injectors and this ground will be connected to the V-terminal of the MOSFET module. When controlling, the injectors will be identical at the same time for the same period. The connectors of the wiring harness that go to the injectors can only be connected in one orientation, which guarantees the correct polarity on the injector, although I think that in this case it would be completely irrelevant.

In the next article we will show the final wiring, the overall installation. We will verify whether the MOSFET handled the current requirements of this application, or whether a change to IRFZ44N was necessary. We will see what condition these injectors were in. Maybe we will also look into the injectors and replace the microfilters in them, or we will also clean them with a cleaner for dissolving carbon and deposits. Sometime in the future we will also remove the injectors from the car (With the entire rail), where they are currently 195 thousand km from the factory and compare the results and maybe we will also try this original injection rail with injectors in the car, which will undergo cleaning.

The next article would not be so extensive and therefore only in the form of an update here.

The initial test was performed without a fuel pump and fuel, only with the injection rail itself and the injectors on it. For testing purposes, I used a power supply with a 12V 3A output on the DC jack. The strip worked fully with all injectors, and it was also confirmed that a 3A power supply is sufficient for these injectors. For the final version, an ATX power supply was used, since it was necessary to power the 12V fuel pump, which produces a pressure of 3.8 bar at the output, and the test power supply probably would not have been able to do that. So far, everything seems to be fine, the MOSFET is handling it, I did not notice any heating. The standard injector opening time is 8 to 20 ms, which is a short time.

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