Limp mode without error messages?

This entry will be dedicated to the topic:

how important is for all N43/N53 (sub) systems to work perfectly. This time we put the accent on “all systems” because there are no unimportant systems!


As already mentioned in other entries, only, if all engine systems (including NOx system) are performing as intended by manufacturer, MSD will correctly perform test of chemical and mechanical efficiency of cylinders and turns on individual corrections and adaptations for fuel, injected in the cylinders, to ensure max even performance of the engine in all modes.


Unfortunately, neither ISTA nor INPA displays status bits, are these adaptations turned on or not – does the engine performs in full functionality mode or not.

Most reliable indirect indication: live data of injector’s opening and multiplicative adaptation: ../F5/Shift + F6/F1.

First three lines show opening time of the injectors; next three lines – coefficient of each injector’s multiplicative correction.


Possible scenarios:

a) both offset type and multiplicative corrections are turned on (full functionality mode) – injector offset (when the engine runs evenly in idle) and multiplicative correction data between injectors are relatively significantly different;

b) multiplicative adaptations are turned on, but offset type corrections – turned off. In this case, we see, that multiplicative corrections are significantly different, but opening times (when the engine runs evenly in idle) for all injectors are very similar;

c) both multiplicative and offset type adaptations are turned off. In this case – coefficients of multiplicative adaptations are very similar for all injectors, also the injector opening times, when the engine runs idle.


Indirect confirmation, that offset type adaptations are turned off – Rough run data (../F5/F7) show persistent (longer than 5 .. 10 seconds in one “polarity”) differences of efficiency – the cylinder efficiency doesn’t converge to 0.


In the image: all corrections (both offset and multiplicative) are turned on, the engine runs in full functionality mode. Differences of offset adaptations typically are in range 10 .. 15 %, differences of multiplicative corrections are at least 5 .. 10 %.


In the image: MSD has stopped both offset and multiplicative corrections, their differences in this situation typically don’t exceed 4 .. 6 %.

Exactly – very similar injector opening times and identical proportional coefficients don’t mean perfect (very similar) injectors, it means – the corrections of injectors are turned off! Even, if the injectors truly are with very similar parameters, mechanical model of each cylinder (friction, valve opening etc.) are different, and the possibility, that the sums of all variables will be identical, is infinitely small.


And at this moment it’s worth to mention some samples form as if unrelated systems, the defects of which can cause limp mode for the engine (without additional error messages about it).


1. Oil pressure. Even the error message regarding oil pressure data plausibility (short-term pressure/PWM unconformity), even if the status of this error message is passive – offset type adaptations for cylinders can be turned off. If, for example, decreased oil pressure with increased engine temperature (ECO mode) will be detected, additionally, the thermal management of the engine also will be modified (ECO mode will be prohibited – possibly, the engine will be forced to perform in Mapped mode – with decreased temperature);

2. Problems with water-pump, communication with it, heating of thermostat. Also in this case – offset type corrections will be turned off, even if the status of the corresponding error message is passive. Moreover, the thermal management of the engine will be turned off by changing the flow-rate of the pump; in case of pump’s communication problems the temperature of the engine will be stabilized, using PWM of thermostat heating (and maintained around 90oC);

3. Fuel pressure. If the error messages regarding fuel pressure (both low-pressure and rail system, also even plausibility) is detected, both type adaptations (offset and multiplicative) are turned off. Also, the creation of LTFT for both banks can be stopped – even in situations, when the status of the error message is passive. Even more – several specific error messages (regarding pressure plausibility) are stored only in Info or History list and are not visible, using ISTA. As a result – the situations, when the functionality of the engine is not satisfying (uneven idle, persistent vibration both in idle and low/average load), but (for ISTA D) no error messages are recorded.


Exact conditions, in which moment exactly the creation of cylinder’s individual adaptations is stopped, are not known. There are many options – by the timer, after a count of error message events, after unsuccessful adaptation cycles etc. Because of this, each situation has to be evaluated “in life”.


In all samples – even, if the error message/problem is identified for short moment/one driving session, the application of corrections will be switched off and MSD will not restore the functionality before the procedures, described below, will be performed.

Even more – if these error messages are deleted, nothing (except very similar opening times of injectors and multiplicative correction data) shows, that the engine has any problems in its performance!


How to solve such problems?

1. All possible systems are connected with each other; for the engine to run correctly, no error messages (with active status) could be present in none of the systems (even if it seem’s unimportant and totally not connected).

2. When problems with all engine systems are solved:

a) delete the error message memory (all error messages should be with passive status);

b) delete adaptations of damaged knots ..F8/F1/..;

c) delete all 2nd group adaptations (fuel trim) ../F8/F2/Shift+F9;

d) re-adapt the engine*.

*related entry/detailed information: Error messages. Part 2


At the end – one of many samples.

Problem – the engine has a persistent vibration in idle. Error message list: no error messages, which could be directly connected with fuel mixture or it’s creation, are present.

Rough run data confirm permanent unevenness:

As seen, cylinder No.6 (according to firing order) has decreased efficiency but is not balanced (increased). Previous (No.5 in firing order) has increased mechanical efficiency, which actually doubles this defect (total difference of cylinder efficiency reaches 0.8 points).


The injector opening data show “perfect” situation:

As seen, the opening times of injectors are practically identical – no offset type adaptations applied to injectors! Multiplicative corrections are applied – no problem with that: in the working mode the engine performs evenly.


Suspicious indication: error messages regarding communication problems with water pump (and with passive status!):


After solving the problem, deleting the error messages, clearing adaptations and re-adapting of the engine, injectors suddenly are “damaged”:


But the performance of the engine is normal – the vibration is gone. It’s confirmed also with Rough run data:

As seen, the deviation has decreased for around 3 times, Rough run values are regularly changing the polarity. Moreover, we see, that now the MSD has “noticed” decreased efficiency of cylinder No.6 (in firing order) and is even re-compensated it in short-term (continues to create offset type adaptations for injectors). Permanent differences in efficiency are gone!