Today in my experience I “met” a car: E90, N43 series engine. It was not possible to start the engine. The starter was turning, live data of injectors indicated, that the fuel is injected, Rail pressure: 100 Bar, but – the engine didn’t want to start.
Finally, after repeated starting, the engine reached the RPM of idle, I managed to keep a range of 2000 .. 3000 RPM, using the accelerator pedal. When slowly releasing the accelerator pedal and when the RPM dropped, the engine started to shiver, integrators started to increase rapidly (reaching +30%), the engine tried to stop. In the error message memory of DME – the error message regarding EGR adaptations and indications of the differential pressure sensor.

When we look at the EGR adaptation data, we see the following picture:

Yes, it is clear – there are serious problems with EGR. Both – wide and narrow opening adaptations – are without the range of allowed values. Obviously, EGR has stuck in half-open/open position. Naturally – also the error messages regarding the pressure sensor, because the inlet manifold is not air-tight anymore – it has no depression in the moment of start/in the mode of the small opening of the throttle valve.

In this entry, I will explain shortly, why such defect of the EGR is so fatal (as I already mentioned at the beginning of the entry – the car can not be started).

In the moment of starting the throttle is opened in the angle of 5 .. 6 degrees – it is determined by the spring in the throttle itself. In the moment of starting the throttle is not managed electronically. Such a solution is intended exactly for cases, when/if the throttle is damaged (it has all possible defects – its electromotor doesn’t function or some of the sensors is lying etc). In the moment of the start, you can choose any position of the accelerator pedal (simply saying – press the accelerator), DME will ignore it. This is one of the aspects, which makes the starting of the car difficult if the engine has fundamental problems with a fuel mixture – the “additional gas” is not possible. From the other side – yes, of course, such a solution excludes flooding of the spark plugs and an overload of the engine in the moment of start.
The second aspect – the EGR valve itself. The EGR valve has a large cross-sectional area because it is intended for much larger airflow as in idle (or even more – around/only 200 RPM mode in the moment of starting). Even, if the EGR has stuck in a half-open position, it can cause (and causes) huge suction of an additional air – the fuel mixture will be very lean, it will not ignite. The car can not be started!
Several nuances are making the situation even worse – when starting the engine of the car, at first parts of the second (till the oil pressure reached a necessary value of 2.6 Bar and a zero position of the crankshaft is determined), the fuel is not injected in the cylinders. Only air, which is pressed in the cylinders, gets in exhaust. Further – the air, which is in the exhaust system, gets back to the inlet manifold via (damaged) EGR, where it mixes with the fuel mixture and “dilutes” it. Unfortunately, these engines have no even Valvetronic, which could reduce the too large amount of the air.