A reader of my blog sent me an interesting e-mail:

I was reading your article – https://bimmerprofs.com/trouble-with-injectors/ – and you say:

“Additional problem – leaking in the closed condition (yes, leaking till allowed threshold is a normal situation, the manufacturer has intended it!).”

The check that’s recommended is that you leave the car overnight, remove the spark plug the next day, and if there is petrol on the tip of the plug, then you have a leaking injector that must be replaced.

So, I thought that the injectors are not allowed to leak and if they leak, then you have to replace them?”

How is it really – the injectors allowed to leak or have to be replaced immediately?

First, I will clarify how the leaking of the injectors manifests. I will talk of idle and cold start modes because precisely in these two modes, the leaking of the injectors is most prominent. I will break it down into 5 stages:

a. the injector is not leaking at all. A case of a perfect injector. In Stratified charge mode, ../F5/Shift+F6/F5 indicates slight correction (to +/-0.10mg/stk). In Homogeneous mode, Offset LTFT is slight and stable; even during a cold start, Integrator is below +/- 10%. Yes, once there were such new injectors – I’ve seen such data;

b. the injector leaks slightly. Its leaking does not significantly impact the engine’s performance – DME manages to compensate for this problem completely. ../F5/Shift+F6/F5 menu indicates adaptations till +/-0.50mg/stk; flowrate corrections both in ../F5/Shift+F6/F3 and in ../F5/Shift+F6/F5 are till the range of +/-5 points (which corresponds around +/-8 .. 10%). Offset LTFT are in the allowed corridor (+/-1.0 ..1.5mg/stk N43/N53). Integrator during cold start is correct: up to +/-10%;

c. the injector leaks quite significantly; its leaking has an impact on the performance of the engine. A permanent vibration can be felt, and the load on CO2 catalytic converters increases. As the density of misfires increases, EML (Check engine) is possible. Injector leaking compensation ../F5/Shift+F6/F5 fits in range 0 .. -3.00mg/stk. During cold start, Offset LTFT has reached the minimum limit (-1.00/ .. 1.50mg/stk N43/N53); the Integrator drops to -30%, and the fuel mixture in the bank can get even rich for a moment (despite all DME efforts to prevent it). ..F5/F7, we see that the difference in the mechanical efficiency of cylinders is above 20 .. 30%; 

d. the injector leaks significantly. ../F5/Shift+F6/F5 reaches -3.01.g/stk; the appropriate error message regarding fuel mixture problems is recorded. The Stratified charge is switched off. During a cold start, the EML lights up. Cylinders are switched off (the fuel mixture in cylinders, which injectors are not leaking, is lean). The error messages regarding rich fuel mixture in Homogeneous mode are recorded in the DME. In the Info list, the error messages 2FDA and 2FDB are recorded quite often – they indicate that HPFP is not able to pump the required Rail pressure;

e. the injector has stuck in a half-open of the completely open position. In this case, EML lights up (or even blinks). One or even more cylinders are switched off – DME (true thou – very often without any success) tries to identify the culprit and reduce the problem. A large smoke cloud comes out of the exhaust pipe. HPFP is switched off, and the injectors receive 5 bar pressure from LPFP. Typical error messages in the Info list – 2FDA, 2FDB, in their attributes – very low (below 30 bar) reached Rail pressure during the start, before the HPFP has been switched off. In the list of basic errors – error messages regarding rich fuel mixture, switched off cylinders. 

Leaking of the injectors is mentioned in TIS. It is indicated that DME measures the leaking of these injectors and, using adaptations, compensates for it (of course, in the range of ability). How the measuring and compensation are executed? Performing the tests of mechanical and chemical efficiency of cylinders! Read more here, here, and here and in other blog entries. Of course, no one has canceled the multidimensional LTFT adaptations and STFT – these tools also are used to compensate for injector leaking.

Compensation for the injector leaking (in full amount) is possible in the case mentioned in point b, and partially possible in point c (yes, the engine vibrates in idle, but no EMl lights up in KOMBI). In situations mentioned in points d and e, DME is not able to compensate for the defects.

Several nuances regarding the leaking of the injectors:

a. remarkable dripping/leaking (scenarios c, d, and e) can be sporadic and “floating”: with changing amounts; more pronounced – when the temperature drops (during a cold start);

b. the dripping can appear after a short-term opening of the injectors and disappear again when the injectors are held closed for a longer time (starting from several seconds to minutes/hours);

c. dripping very often disappears completely when the Rail pressure is reduced. For example, by the pressure of 180+ bar, the injector leaks; by the pressure of 150 bar – no leaking at all;

Returning to the method mentioned by the blog reader – it can be described very shortly: FAIL. Why? 

a. when the engine is switched off, Rail pressure drops to 5 bar for several seconds, accordingly – even strongly leaking injectors will typically indicate no problems;

b. as we know, petrol evaporates, accordingly – for the cylinder surface to be wet after a longer time, the injector should leak very strongly. The injectors with defects, mentioned in points b, c, and d, will not leak by the pressure of 5 bar. 

The conclusion is simple – by using this “method”, only injectors with catastrophic damages (worst scenario of point e can be identified.  

If the user has no access to any diagnostics equipment, I suggest a more coherent method, which is described here. When using this method, at least the Rail pressure is increased. But – this method is also valid for identifying injectors that are leaking very strongly. 

Summary – the leaking of the injectors should be evaluated using data from INPA diagnostics. Mechanical methods (even increasing the Rail pressure to 150 .. 200 bar) allow for identifying only catastrophically damaged injectors. The answer to the question at the beginning of this entry: of course, the injectors, which are stuck in an open position and are flooding the combustion chamber with fuel even by pressure of 0 .. 5 bar, HAVE to be replaced immediately. At the same time – the topic of the leaking of piezo injectors is much more complicated than it seems at first glance.