F07 N55. Long cranking

Today’s patient: F07 GT with N55 series petrol engine.

One of the complaints: the engine takes a long time to start (especially after longer stand, cold start).

 

Several specialized BMW centers have performed the “diagnostics”. Suggestions: replace LPFP, HPFP, injectors, the starter, the battery.

 

The initial inspection identified the error messages regarding IBS sensor. Of course, if the car is not able to monitor the charging and status of the battery, it (the battery) will not be used correctly. For incomprehensible reasons, none of the specialized service centers has noticed this problem.

Have to add, that the problems with an IBS system can be the cause of irregular long cranking – IBS is measuring the start current of the battery.

Also, if the battery is not charged appropriately, the starter will not be able to turn the engine at the moment of starting and the starting can be problematic.

In this case, after replacing the IBS sensor, the calculation of the energy of the battery was restored but the problem with long cranking didn’t disappear.

 

Next obstacle, which can cause long starting: insufficient oil pressure.

I connected ISTA D. When starting a cold engine, I detected, that at the moment of the start the oil pressure slowly rises and reaches around 2000 hPa during approximately 5 seconds, then suddenly the engine started to work but the oil pressure in idle reached 7000 .. 7500 hPa!

What does means the indication (of such high pressure)?

During max allowed starting time (around 5 seconds) the necessary minimal oil pressure was not reached, so:

a) when the max starting time ended, the engine (however) was started;

b) DME disconnected the management of electronically manageable oil pump (because the problems with oil pressure were indicated) and making it work with a max pressure.

 

This protection mechanism (long cranking) is intended for all N43/53/54/55 series petrol engines (which have electronically manageable oil pump) to protect them from mechanical damage due to insufficient oil pressure.

In case of such problem MSD80 DME records the appropriate error message in Info list error message list. In attributes the data of the moment of starting are indicated: typically around 200 RPM and max indicated oil pressure below 2000 hPa. Info list can be seen only using INPA (ISTA D/+ don’t allow to see this list).

Unfortunately, other DME doesn’t have this Info list; Bosch DME doesn’t record an error message in such a situation.

It may seem strange – the engine has such serious problems with the oil pressure, that all system of the oil pressure stabilization is turned off, but – no error messages? Yes, unfortunately, it is so. Repeating several sequential cold starts, the problem repeated. Long starting, low oil pressure, then – the engine starts and the oil pressure around 7000 hPa. There was no smallest doubt, that this problem is an occasional case.

Note: N43/N53 series engines with MSD80 DME management in such situation (if at the moment of starting the necessary oil pressure is not reached) maintains the mode of max pressure for a short moment (several seconds) and restores the electronically manageable oil pressure mode as soon the correct oil pressure is reached.

 

What to do in such situation (if there are suspicions for insufficient oil pressure as a cause of long starting)?

Connect ISTA D (in an ideal case – via iCom, because iCom ensure slightly faster data refresh as USB connection cable).

Perform the vehicle identification, choose DME module and select live data you are interested in.

To ensure max fast refresh rate of data, choose a minimal number of data. In this case, it will be enough with:

a) oil pressure;

b) RPM of the engine.

In this video you see, how I start the engine several times, then turn it off and wait for a moment. The engine is already partially warmed up, so the defect mentioned above is almost hidden. After the engine starts, DME stabilizes the oil pressure (target value in idle is around 2600 hPa) – the oil pressure management system is turned on. Also, the starting happens much faster. And still – you can see, that the oil pressure gradually rises during around 2+ seconds. The oil pumps of N53/54/55 series engines are very powerful – they have to be able to pump a necessary oil pressure (around 2600 hPa) immediately. In this video it doesn’t happen – the oil pressure rises reluctantly.

 

There is no doubt – the car has serious problems with reaching the oil pressure during the moment of start. Following items have to be checked: the management valve of the oil pressure pump, oil filter its back pressure valve. The oil pump itself seems in good technical condition, because already by 600 .. 650 RPM it can reach a pressure of more than 7000 hPa.

 

P.S. Also in this entry I will remind you: HPFP is not one to blame in case of long starting! DME “sees” the Rail pressure and recalculates the opening times of the injectors according to the actual Rail pressure. Even several times reduced Rail pressure will not interfere with maintaining the correct fuel mixture. Even more – even with completely turned-off HPFP, the engine starts normally (the Rail pressure of around 5000 hPa is provided by LPFP).