Quite often we hear, that N series engines (more often regarding 4 cylinder versions) has long starting time. No other claims. The engine has to be started for a relatively long time, then suddenly it starts as if nothing happened.
Of course, the fuel pressure has to be checked. For N43/N53 series and newer engines, if the fuel pressure will be lowered, an appropriate error message will be recorded. The problem can be an obstacle, that these error messages (sometimes, by unknown reasons) are stored in Info list or, if they have been recorded in the Error list and deleted – in History list (if the particular DME has it). Both Info and History lists can be seen only by INPA, ISTA D don’t see these lists (it means, that also the repair specialists in dealer centers also don’t)!
For older N series engines, for which the fuel pressure is stabilized, using mechanical fuel pressure regulator, it is self-understandable – no error messages regarding in case of decreased fuel pressure will be recorded.
Accordingly – if the engine starts very lazy, the fuel pressure has to be checked at first hand. The fuel pressure problem has one more symptom – at the moment when the engine starts, it increases RPM (till required RPM in idle) very lazy, as if “bullying”. It happens, because the fuel pressure is pumped slowly – in the beginning, the fuel mixture is lean, typical situation – misfires. In turn, if the engine suddenly starts as if “by magic” – correctly, fuel pressure problem will not be the one to blame.
I suppose, that basic things are checked – does the crankshaft sensor sends information in the moment of start (using INPA/ISTA live data), the engine has no error messages regarding air meter, throttle, Valvetronic and similar.
The problem, described below, is not mentioned in BMW literature and are only my personal observations. N series engines are using an electronically stabilized oil pressure management system. Accordingly, as opposed to “older” engines, N series engines “see” precise oil pressure.
These data allow both to precisely regulate the oil pressure (a critical need for performance of Valvetronic/HVA) and control it in the moment of the start of the engine.
My observations suggest:
- for the fuel to be supplied in the cylinders (the engine would start), in the moment of start the oil pressure has to reach threshold X (this threshold is not exactly known, because the measuring is very complicated, information from the manufacturer – zero;
- if in the moment of an engine start (reaching around 200 RPM) the required oil pressure (around 2.6 bar for the warm engine, to 3.0 bar for the cold engine), the engine stabilizes the fuel pressure according to the DME map from the first moment;
- if at the moment, when the engine starts, the required oil pressure value is not reached, directly after engine start DME keeps the oil overpressure valve closed and tests max oil power. When the oil pressure reaches (stable) max and this value, obviously, is checked (evaluated and is enough), DME starts the maintaining of the oil pressure according to map;
- if max value, measured by DME, is decreased, or – even after long start threshold X is not reached, the error message regarding lowered oil pressure in the moment of start is recorded, DME switches off oil pressure regulation system till next driving session and maintains max oil pressure (the same as in case with defective oil pressure sensor).
Obviously, BMW engineers, understanding, that decreased oil pressure in the moment of start can have several causes (description will follow), which directly don’t direct to the defect (with condition, that max reached oil pressure is correct), allows such situation with decreased oil pressure, and the error messages are not recorded. From the other side – if the oil pressure is zero, it’s not allowed to start the engine. Yes, in old times, for “old type” engines such situations happened – for some moments after the start the oil pressure indicator continued to blink, but such mode can be deadly for the engine.
Note: if DME has detected such problem (not sufficient pressure) when starting, it’s very possible, that during next X start cycles the testing of max oil pressure will be performed even then, if in the moment of the start that would be correct. Not knowing exact work algorithms, I cannot state precisely – there, in such cycles, in such conditions (temperature of engine and oil) DME will test the oil pressure in such way, for so many cycles – will start longer, because will require more thorough confirmation for reached oil pressure in the moment of the start etc. (Additionally, these conditions could be significantly different for different software releases, and also – it depends on that, which team – Siemens or Bosch – has developed this DME software). But, if we take as a sample/ analogue, for example, work algorithms of cooling system, I have the reason to think, that oil pressure control could be quite complicated solution: with separate algorithms, if the decreased oil pressure is detected for hot and cold engine, in the moment of start, with low or high load etc.
Note – the complexity of these algorithms is confirmed by fact, that, for example: if decreased oil pressure is detected in normal/ECO mode, the engine is switched to Mapped mode (with decreased temperature); if it doesn’t succeed to maintain the oil pressure also in this mode, max oil pressure mode is turned on etc.
The main regularity – if in the moment of start (INPA/ISTA data, if they are available, or readings of manometer) the lowered pressure is displayed; if directly after starting the oil pressure for several seconds reaches high value (above 3.0 bar) – there is a cause for serious suspicion.
The situation is more complicated by the fact, that there is no information regarding algorithms and their changes, depending on data of oil “quality” sensor. Also here surprises are possible (necessary threshold, which has to be reached in the moment of start, can change etc.).
Additionally to mentioned before – very often (more expressive, for example, for N43 series engines) in the error message memory the error messages regarding oil pressure (lowered pressure or plausibility) are recorded. What usually the service centers are doing in such situation (I believe, in 99% of cases)? Correct, these errors have to be simply deleted. What does the SB, issue by BMW, say? Solve the problem, perform re-adaptation of the engine. Only when all (old) adaptations are deleted, also other, unavailable in a different way, status bits, which restore full functionality of DME, are deleted. In turn in case of “solution” of the first scenario, these error messages regarding oil pressure problems are hidden for some time, full functionality is not restored (including – a series of specific adaptations are turned off – the engine will continue to work incorrectly).
There can be several causes for insufficient oil pressure in the moment of start:
- oil has lost its viscosity (the problem will be more common for the warm engine). Causes – bad quality oil, “aged” oil, oil, diluted with petrol (the cause – leaking injectors);
- oil leaked from the system (filter). Causes – defect of oil back valve (placed in a bottom part of oil filter cover) or dirt, which has gotten inside;
- partly clogged oil catcher, decreased flow-rate of oil pump, oil pressure (electrical) and overpressure (mechanical) valves are not closing, increased oil consumption (wear of shawls, worn seal rings of VANOS, etc.).
Unfortunately, this problem is of mechanical origin and there are no simple diagnostic possibilities to “press the button on the computer” or simple solutions. What can we do? for example, turn off the fuel pump, turn off the oil pressure regulation valve, connect the manometer to check the oil pressure and measure – how quickly and what pressure the oil pump reaches at the moment, when the engine starts, disassemble several hubs (oil pump, VANOS etc.) to evaluate their condition.
As already mentioned in other entries, in idle the oil engine for N54/N53 and similar N series engines is max able to reach 4.5 .. 5.0 bar high pressure. Instead, the inquired value (electronically stabilized) of oil pressure is 2.6 .. 3.0 bar. These characteristics can be as the reference point.
Problems with oil, it’s quality and pressure are very common! Most popular causes:
- inadequately long intervals between oil changes. BMW in it’s SI materials for sales has remarked – in the moment of sale, the salesperson has rights to define shorter oil change intervals as defined initially, after evaluating the buyer’s driving profile. Unfortunately, in practice, no one usually does it. Even more – when buying a used vehicle, this system doesn’t work even by the idea. Instead, in the moment of sales of a new vehicle, the guarantee “works”, the customer wants to get the car as cheap as possible, not overpay for maintenance etc.;
- oil of inadequate quality. In this case also oil change services are “sinning” (even the customer pays for oil of higher quality, they manage to use oil of lower quality), very common is the sale of forged oil (the brand names are forged, and the cheaper oil of the same brand is sold as more expensive one);
- quite often (due to ethical reasons I will not mention – how) in the process of oil change around 1 liter of oil is smuggled – this one liter stays the old oil. So the services are “saving” quite significant amounts of oil (saved oil is used for their own cars or sold to customers once again);
- quite often I see the situation when only one of two main elements is replaced – either only oil or only oil filter. The cause can be very different – the human factor (oil change is usually assigned to apprentices or specialists with lower qualification – it’s so simple task, also a wish to save time and money (for example, the necessary filter is not available on stock, it can be delivered only after a long time);
- oil is diluted with petrol. Quite common myth – in an ideal scenario, the engine don’t consume oil. No, the engine has to consume the oil! If the engine doesn’t consume the oil (there are even cases when the oil level rises), several causes are possible – for example, clogged crankcase ventilation or leaking injectors;
- problems with oil pressure due to mechanical issues, for example – the debris of damaged chain retractors have gotten in oil catcher and oil channels;
- and finally – the irresponsible action of vehicle users. The oil is not changed in time! Driving in hard conditions (in the city, with low average speed), oil is replaced only then, when the warning sign regarding overdue oil change interval is burning, cheap and low-quality oil is used, cheap and low-quality oil filters are used.
And one more nuance – if in the past, the oiling of the engine was done in a poor quality, the problems with oiling will persist, even when starting to use high-quality oil! The wear of crankshaft shafts and oil pump, clogging of oil pressure valves, clogging of oil channels and oil quality sensor don’t go anywhere! Very often, serious maintenance of the engine is necessary to avoid consequences of poor oiling. There are also cases, when, unfortunately, the engine has to be replaced – it’s not possible to help anymore.
These are only several of causes, why the engine can have serious problems with oiling system. Yes, the problem is unpleasant, it’s solution – time consuming and expensive. So it’s more profitable to change the oil timely (after each 10 .. 15.000 km), use high-quality oil and oil filters, entrust the oil change only to service with reputation, avoid unjustified “cheap” offers.
