Does it make sense to replace the injectors after some certain interval? What would be that interval?


I think, that this question is up to date for each car user, who has technical knowledge. Piezo injectors are more capricious (they “clog” easier), N series engines – more complicated, they more often are troublesome. Accordingly – the topic regarding replacing of injectors is especially actual: what if the cause of all troubles is “bad” injectors?


Right away I will mention my observation – regular (and all – in case of some problems) replacing of injectors is promoted by repair “specialist”, who are not able to identify the cause of the problem (what, probably, is located in totally different hub of the engine) or is not able identify the “guilty” injector.


There are specialists, who scare with a hydro blow. As I already calculated – it is not technically possible, also practice, collecting information regarding more than 1000 pieces of N43/N53 series engines, confirms – no case of hydro blow due to leaking injector was confirmed.


As I already mentioned before, for example, hard microparticles (dirt, debris etc.) can get in the injectors and “damage” in any moment, this defect is not related to the aging of the injector.

Defects, which could be related to the aging of the aging, are rare. One of such cases is described here.


Let’s assume, that the specialist, who performs diagnostics, knows, how to identify the damaged injectors and in case of defect, if necessary, replaces only it.


Let’s look at the following topic – does the parameters of new and used injectors are significantly different, how the parameters are different from ideal (defined by manufacturer). It means, we will try to find out, do these data are “floating” during the time – does the difference from ideal parameters (measured and described in calibrating data), defined by the manufacturer, grows, does the jittering of data grows.


For comparison I use self-diagnostics data of MSD80, displayed by INPA:

  • offset type adaptation data in idle/Stratified charge;
  • live data of injectors (opening times and multiplicative type LTFT);
  • data of chemical tests of injectors (relative differences, low and high load);
  • Rough run data (mechanical unevenness, idle).

I paid special attention to corrections of injectors in idle/Stratified charge because this is most critical mode: very short injector openings, test results – change promptly, if the unevenness in the performance of injectors and ignition system, is present – it can be seen immediately


Let’s describe two engines:

The 1st engine has a mileage of around 150’000 km

  • replaced CCVV;
  • new spark plugs, ignition coils;
  • new injectors;
  • preventive repair of the engine was performed: new valve seals, piston rings;
  • new VANOS valves;
  • installed NOXEM, the engine uses Stratified charge.


The 2nd engine has mileage around 380’000 km

  • CCVV is not replaced;
  • the spark plugs have worn for around 25’000 km; ignition coils – around 100’000 km (snubbers installed);
  • 4 injectors have wear above 300’000 km (release 07), one – around 170′ 000 km, one – 10’000 km (for the both last release – 11);
  • no repair for the engine has been done;
  • nor VANOS valves, nor inlet manifold have been cleaned;
  • installed NOXEM, the engine uses Stratified charge.


The owner of the 1st car in some internet forum has found information, that due to open injector the hydro blow is possible, has decided to replace all injectors. I was asked to check the engine already after replacement – to encode new injectors, re-adapt the engine.

The replaced injectors were encoded, the engine – re-adapted. Best achievement in Normal mode temperature mode:

As we see, only one injector required correction of -0.28 mg/stk. For others – very tiny.


True though, in other temperature modes the correction of injectors reached around +/-0.40 mg/stk. (0.28mg/stk corresponds to correction of around -5 %; 0.40 mg/stk corresponds to 7 % difference from ideal).


Rough run indicated typical deviations till +/-0.005 units from ideal. For this software release, 0 efficiency corresponds to 0.2000 units, accordingly – unevenness of cylinders: till around +/-2.5% (or to 2.75, taking in account the data resolution).


2nd engine after re-adapting:

As we see, the worst (far from ideal) result is for the injector of 3rd cylinder: +0.25 mg/stk (around +4 %). This is injector with the wear of 170’000 km. In the same time the wear of injectors for cylinders No.1, 2, 4 and 6 is above 300’000 km, but correction – close to 0 (less than several %).


Rough run data indicate typical unevenness to +/-0.200 units. Zero efficiency corresponds +7.000 units, accordingly – unevenness: to around +/-2.9 %.


Tests of chemical efficiency for both engines in low and high load mode indicated small differences between last and before last test results (to +/- 1.0 units).

The injector opening time in a Homogeneous mode for both engines fell into the corridor of +/-5 %.

Multiplicative adaptations of injectors of both engines fell into the corridor of +/-5 %.


I made a clear conclusion for myself – the resource of piezo injectors is considerable. I haven’t seen the “degradation” of their parameters due to wear. As we see, data of injectors (measured by MSD80 – there is no reason to not believe them) in quality are not different for new injectors and injectors with the wear of 300’000 km. A much higher impact to the injector corrections in idle/Stratified charge has, for example, turned-on AC, the rapid increase of inquired consumption of alternator, detail play of the flywheel (if the car has manual gearbox), misfires.


Summary – piezo injectors are of high quality and with long lifespan! There is no rational basis to replace them regularly.


P.S. for the 2nd engine, two of six injectors are newer. Why they were replaced? In both cases – the injectors started to leak. Idle/Stratified charge menu indicated, that large negative correction is required to even the efficiency of the cylinder. In the same time – multiplicative type adaptations for both injectors were correct, beam – obviously correct (the engine performed normally in Stratified charge). One of the injectors started to leak after around 200’00 km, second – after around 120’000 km.