copyright 1998-2018 by Mark Verboom
ipv6 ready RSS Feed Schakel naar Nederlands

Go back to Opel Speedster 2.2 16v

LSJ Injectors

As preparation for fitting new camshafts, I also need to select a new set of injectors. The engine in current trim is pushing the standard injectors pretty far. Last year we measured a dutycycle of 93% (Speedster injector test).

The most obvious choice are the injectors used in the LSJ engine. They flow quite a bit more and should be sufficient for higher power levels.
A while back I bought a set of 16 through ebay. I then made my own injector testbench, so I can test the injectors and try and match a set of 4 with similar specifications. As the injectors are second hand, this is a useful precaution, but even with new injectors it can be very helpful to know the injector performance.

The testbench consists of:

  • A power supply of 13.8V with over 20A of capcity
  • Electronics board with USB interface, amplifier for the injector signal, outputs for camera and flash and controls for the fuel pump
  • Netbook, interfacing with the FTDI board in the electroncs box, generating the test signals
  • Fuel rail from a speedster
  • 4 graduated cylinders (100ml)
  • Small fuel container with pump and adjustable pressure regulator


The idea is to run 2 separate tests. The first one is to run a number of different RPM and duty cycle tests and see how much the injectors deliver. The second test is to take photo's of the injectors opening and closing, looking at the spray pattern.

For the first test a number of different test programs were created, ranging from low RPM and low duty cycle to full open. Below is a short movie of the start of the 800RPM, 2% duty cycle test.

And the test at 6400RPM with 72% duty cycle.

The results for the selected set of injectors were:

TestInjector 1Injector 2Injector 3Injector 4
800RPM, 2% duty cycle, 10 minutes71ml71ml70ml71ml
800RPM, 4% duty cycle, 10 minutes73ml73ml73.5ml74ml
3200RPM, 4% duty cycle, 5 minutes53ml52ml52ml53ml
6400RPM, 25% duty cycle, 50 seconds72.5ml72ml72ml73ml
6400RPM, 72% duty cycle, 17 seconds74.5ml75ml75.5ml75.5ml
100% duty cycle, 10 seconds64ml64.565ml64.5ml

As you can see in the table, the values are pretty close together.

The next test is the spray pattern. To capture images, I made two separate connections. One goes from the electronics box to my Canon 50D camera and one to the Canon Speedlite 430EX flash. The software then controls the triggering. First the shutter of the camera is opened and the the flash and injector are triggered with different intervals.


Below is a short (and a bit dark) movie of the whole event.

Using this setup, some interesting pictures can be taken. Below are all 4 injectors starting to open.

Injector 1

Injector 2

Injector 3

Injector 4

You can see the 2 nozzles in the injector, each aimed at a valve. You can also see the spray patterns are the same over the 4 injectors. There are no big deviations like with other injectors I had on the test bench.

So, this is the injector set that is going on the engine.
Putting the injectors on the engine can be a bit of a fiddly job. In the pictures below you will see the engine without the cover. To replace the injectors, you don't need to remove the cover. First remove the air intake to create space.


Bleed off the pressure on the fuel rail.


Loosen the fuel lines that go to the fuel rail.


And remove the fuel lines.


Remove the screws holding the injector rail to the head. If required remove the ECU plugs to create more space. Then try to remove the injector plugs and pull the injector rail with the injectors from the head.
You should end up with a fuel rail.


Remove the old injectors, put the new ones in place and don't forget to place the clips.


Put a small amount of oil on the rubber rings of the injectors. That will ease installation.


As the original injectors have been on the car for a while (7 years, over 120.000km), we cleaned the ports as much as possible, even using a vacuum cleaner.


Now the fuel rail can be put back in place.


And finish everything up in reverse order.

After a disappointing first engine start attempt, we remembered that we needed to adjust the ECU to take the new higher capacity injectors. So just connect OBDTuner to the car, select the LSJ injectors, write everything to the ECU and start again. It started without a problem this time.