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Piezo Injectors Signature Test

A lot of newer cars use petrol direct injection. It's a far more efficient way of injecting fuel into the engine.

Manufacturers had been using this system on diesel vehicles for quite some time so if you've never worked on a diesel you might not know it's a little bit different.

With a Snap-on scan tool hooked up to the vehicle, we can see how the data looks on a lab scope and how the pattern is actually different than a standard fuel injector.

Inside all of the Snap-on scope tools is the Guided Component Tests section, which gives us a lot of information on how things work and where to connect the tool to the vehicle – let’s use a 2016 Ford Escape with an EcoBoost® motor for this example.

With the vehicle identified, go into the Fuel Injection System menu and then into Fuel System, followed finally by Fuel Injector.

Now the tool going to give us some information so we'll go into Component Information and it tells you how the system operates:

  • The gasoline direct fuel injector delivers fuel directly into the cylinder under high pressure.
  • Each injector is controlled by two circuits from the PCM
  • A boosted voltage supply up to 65 volts is generated in the PCM and used to initially open the injector
  • The injector driver controls three transistors switches that apply the boost voltage to open the injector and then modulates the current to hold the injector open
  • If boost voltage is unavailable, the correct injector opening current might not be generated in the time required

The PCM contains a smart driver that actually monitors each side to see whether there's a problem and it will display a code for whatever the problem happens to be

The tool tells you that the best place to test on these vehicles is either at the injector itself, which can be hard to reach, or a 16-pin connector on the left rear side of the engine, above the engine oil filter housing. That’s where the connection is made for this example.

If you go into your lab scope you can see two different patterns displayed, one after the other.

The second pattern is powering up the fuel injector and contains a small voltage spike at the same time as the amperage goes up.

Did you know that fuel injectors on Direct Injection vehicles work differently than a standard fuel injector? Read on to learn more.

Then the amperage drops down slightly and as that happens, it is modulated up and down to keep the injector open.

As the amperage goes up and down, the voltage follows, which will be visible on your screen. The final spike on the pattern shows when the injector is closed.

So as you can see, the theory here is a little different than standard fuel injectors, but as long as you keep this in mind it will help you diagnose issues.