In this entry, I will describe two as if not too much-connected themes, which actually have a very close connection:
a) CCV problems;
b) self-test of the fuel system.
This time, the CCV problem has hidden very well, and due to this, this case is very interesting.
Patient: E90, N53B30. Some time ago the injectors were replaced; when the problem didn’t disappear, the NOXEM was installed, the engine was re-adapted. Everything was fine – the engine worked in Stratified charge without problems, but after several months the owner of the car started to complain, that the engine sometimes shivers in idle when it’s warmed up.
This time there will be no many pictures, to keep the entry more compact. Regarding defects of CCV and identification of these defects, check previous entries regarding CCV.
DME error message memory had the error messages regarding fuel mixture of both banks recorded. The fuel mixture in idle was lean. Lambda: 1.20; integrators +30 % for both banks. It’s clear, that the problem is common for all cylinders. Approximately (30 + 20 %) = 50 % leftover of air.
Obviously, the engine sometimes has fundamental problems:
a) either the fuel pressure is lowered (incorrect readings of pressure sensor);
b) or the amount of air is increased (air suction problems).
At the same time, ../F5/F6 indicates correct offset type adaptations (+0.02/+0.08 mg/stk: they are confirmed, it means – stable); when starting the engine – everything is perfect. CCV was checked for several times. Yes, the valve closes incompletely, but for a car of the age of 10 years, it’s acceptable with the condition, that the oil consumption is within a normal range. Air suction was not detected. When checking the inlet manifold from inside, the repair specialist indicated, that the oil can be found there. It’s not good news, but all sealings – in perfect condition.
When the engine reached a temperature of around +100 oC, it started to shiver in idle. Misfires can be felt, Lambda in both banks was around 1.20 .. 1.30, integrators for both banks +30 % (..F5/F6).
LPFP and HPFP pressures were shaking strangely. In addition, at one moment it seemed, that there are problems with LPFP, but after a while – with HPFP (../F5/F2/F6).
The manometer was used to control the HPFP. It indicated a difference of +/-5% from data, indicated by DME. So – the HPFP sensor doesn’t lie. Accordingly – DME should be able to maintain correct fuel mixture!
Air consumption: 8 .. 18 kg/h, it’s hard to indicate the average value, because indications are fluctuating strongly (correct reading: around 12 kg/h in Homogeneous mode). When disconnecting the air mass meter (to force DME use only maps of the throttle to adjust the amount of air), it was concluded, that the problem persists. So – measured amount of consumed air is correct.
The openings of the injectors were checked (../F5/Shitf+F6/F1) – they were around 0.3 ms (each of two impulses). Such corrections are correct for the warm engine in Homogeneous mode by HPFP pressure of 200 Bar.
There were not the smallest suspicions left, that in the inlet manifold, the air is sucked. The only question was – where?
The problems can be caused by any connection to the inlet manifold, for example, EGR or fuel tank ventilation system.
Checking the fuel tank ventilation system (../F6/F1/F3), it was detected, that the ventilation valve of the fuel tank is moved in a range of 0 .. 5 %. Stuck of a valve? Non-airtight system? The ventilation valve was locked – no changes.
At that moment, the repair specialist decided to check the CCV once again. When disconnecting the pipe from CCV and blocking it, the problem disappeared immediately. When checking the membrane, we had to conclude, that it’s broken – the air was sucked via the opening at its cover!
Here, an unpleasant defect. Not typical, because the problem was only with a warm engine, only in temperatures above +100 oC. The opening of the fuel tank valve was consequences of CCV membrane problem – DME was trying to detect if the problem of air suction is in this system.
As usual, there is no information from the manufacturer, the conclusions are based on my observations. What would I do in case of this defect (completely incorrect fuel mixture), to make sure, that the HPFP sensor doesn’t lie – the engine has any problem with fuel pressure? Unfortunately, the HPFP sensor is not doubled (as, for example, the throttle or accelerator pedal sensors, or, for example, Lambda probes). Have to think of more cunning techniques.
a) if till now the LPFP system has worked correctly, we assume, that we can trust it. Reducing the PWM to LPFP pump for a short moment (and, accordingly, the power, supplied to the pump), we can observe relative speed of pressure drop in LP contour. So we will get the information regarding the real amount of fuel consumption;
b) the same performing with HPFP (reduce the PWM, supplied to the valve, for a moment), we can observe the drop of HPFP pressure.
If we know the true fuel consumption and drop of HPFP pressure, we can evaluate the trustfulness of the indications of HPFP pressure sensor.
In such way, the MSD checks the fuel system components. Accordingly – don’t be surprised – in conditions, when DME cannot maintain correct fuel pressure, LPFP and HPFP pressures can fluctuate quite strongly (4000 .. 6000 hPa; 150.000 .. 230.000 hPa) for some time. Of course, the cause of such fluctuation can be a leaking injector or stuck HPFP valve or problems of LPFP pump. But also the self-test of the system can make the pressure “wave” in such a way.
At the end simple advice: if the CCV membrane is damaged and the air via CCVV is sucked in the inlet manifold, till the moment, when the spare part supplier supplies a new valve cover, you can do the following:
block the CCV ventilation hole with silicone or some glue. Till repair, you will be able to use your ca without fundamental trouble.
Remember! This is not a complete solution to the problem! CCV will be open for all time, the oil consumption – increased! Replace the valve cover ASAP!