Fuel mixture: rich or lean?

This time as if absolutely simple situation: the error message 29E0/29E1 regarding fuel mixture problems.

What so unusual in this current situation?

Pay attention to the marked words.
In German, “Zu Mager” means “too Lean”! But in the OBD error message description, “too Rich” figures.

First nuance, which has to be taken into account: the error messages 29E0; 29E1 (accordingly for the 1-st and 2-nd bank) are recorded both in case of the too lean or too rich fuel mixture. The name of the error message is “Fuel mixture control”. In the description of the error message is indicated, which problem precisely is identified.
OBD error messages, instead, are separated in case of a lean and rich fuel mixture. For example, in this case: P2190 means too rich fuel mixture, but P2189: too lean.
Obviously, there is a mistake! This is one of the causes why in diagnostics of BMW EDIABAS should be used, not OBD error registration systems. BMW maintains the OBD system only in required “minimum”, paying the primary attention precisely to the EDIABAS (OEM) system.

Why it is so important, was the fuel mixture too rich or too lean? Depending on the situation, the typical causes of the problem will be radically different!

If the fuel mixture was too lean:

  • air intake in the intake manifold (especially crucial in idle);
  • reduced fuel pressure (for older engines: till N52/N46).

If the fuel mixture was too rich:

  • leaking piezo injectors (for DI engines);
  • increased fuel pressure (damaged pressure regulator, clogged fuel feedback for older engines).


But let’s come back to the exact situation. In this case, it is MSD80 DME, an N53 series engine. Here, the error message regarding 1-st bank, with an identical problem – in EDIABAS attributes, the lean mixture is indicated, but the OBD error message is regarding rich fuel mixture.

In additional attributes, we see – the problem was in idle (around 640 RPM, 0 km/h).
”Zustain Lambdaregulung” 2 – it means: DME has used closed-loop mode (the fuel was adjusted according to the data from the Lambda probes), it is also confirmed by status: EIN.
With red, the fuel mixture correction data are marked.
What do they mean? DME has tried to reduce the injected amount of fuel significantly. LTFT (sum of Offset and Multiplicative LTFT) for each of banks – 20.3%, additionally the Integrator has reduced the fuel amount for -25.8%. So – to maintain more or less correct fuel mixture, the amount of injected fuel is reduced for 46.1%!
There is no slightest doubt – some of the injectors were leaking during the time when the error message was recorded os shortly before.
Why has the EDIABAS included “Zu Mager” – “too Lean” in the error message description?
Such a situation is developing if the leaking injector suddenly closes correctly and (even for a light moment) the fuel leaking problem disappears. At that moment DME detects that the fuel mixture (which it was managed to maintain more or less correct, even – reducing the amount of injected fuel for 46%) suddenly has become very lean. DME immediately records the error message.
For this reason, the situation develops as if controversial: DME has significantly reduced the amount of injected fuel and then detected that the fuel mixture is lean.

To make sure of the situation, check the Offset type LTFT, which can be seen ../F5/F6, last line.

Here, Offset type LTFT has reached a minimum threshold. So: in idle, DME reduces the amount of injected fuel as much as possible. Here – irrefutable proof that the injectors are regularly leaking in idle: they inject an increased amount of fuel.