The owner of the car with the N53 series engine from sunny Italy approached me.
The car has been performing quite well, but – as it is not new, the owner decided to improve the engine’s performance. For this reason, he has trusted to clean and inspect the injectors of his car to the local professional company. All injectors have been cleaned and tested, and all test results are as if perfect. Unfortunately, after installing the injectors, the engine vibrates, some error messages appear in the DME error message memory. Where could the problem be?
The company gave the test report of the injectors to the owner of the vehicle. Let’s start with it. I will insert the images exactly as they were sent to me.

As we see, really – results of all injectors marked as successfully performed. But, wait – for better visibility, let’s put all results in a small table:

Do you notice something strange?
R2LC is an electric measurement; it is similar to all injectors. But other measurements – of the injected fuel – are strange.
OK, TP4 is a test of short impulses. Let’s assume that: as the injectors are used, they can have a slight scattering in this mode. But TP1 and TP2 are modes of long impulses. Scattering – more than 2(!) times? In addition – as we see, the injectors are split into two groups: 1 .. 3 and 4 .. 6. The test results of the second injector group are almost two times higher!
Obviously, something has changed between the testing of the 3rd and 4th injectors. The most plausible scenario – Rail pressure has increased around two times. How so? This question should be asked to the performers of the test.
But even in such a scenario – the TP1 test from the 4th to 6th injector is enormously different. 34.8 and 42.3 – the flowrate differences are thorough!
But the most interesting question: how is it possible that the injector results are so different, but all tests are successfully passed?
Here is the answer:

With red, the allowed test values are marked. You still have questions; why are all tests successfully passed? Because the infinitely wide range of permitted values is input! In all tests, the minimum value is 0, but the max – 10 times higher than the even possible values!
Isn’t it an excellent injector test? Wonderful!
Let’s continue with the measurement of DME itself. Here, for example, Stratified charge, idle:

Without even the slightest doubt: injectors No.1 and No.6 are strongly leaking in idle. But also the situation with injector No.2 is poor, this also should be replaced immediately!
And here, the error message in the DME error message memory:

Yes, the leaking of injectors No.1 and No.6 is catastrophic. Even reducing the initial injection impulse for 3 (!) times (-3.02 mg/stk against the reference), DME has detected increased mechanical efficiency of the current cylinder. Unfortunately, the only place where these injectors should be – garbage.
There is no doubt that injectors No.1, No.2, and No.6 should be replaced. Without any illusions – the cold start will not be beneficial for other injectors. Also, the NOx sensor is damaged – its probe is poisoned with the fuel.
What went wrong in this “cleaning”?
The cleaning fluid “goes around”, which means it is collected for reuse after flowing out the injectors. For Piezo injectors, even the slightest micro part is critical. Unfortunately, the “cleaning” fluid fast enough changes to the culprit of the leak.
This time I have bad news for the owner of the vehicle – the decision to clean the injectors cost him around 2500 .. 3000 EUR.
I can only repeat again and again – do not try to “clean” the Piezo injectors!