In this entry – about one of the most expensive hubs of direct injection engines: high-pressure fuel pump.
The structure of HPFP has described in BMW AG after-sales materials, but many nuances are left “behind the scene”. Because of this, there are many misunderstandings and wrong decisions, performing the repair of the car.
Let’s start with statistics – my experience, performing diagnostics of several thousand N43/N53/N54/N55 series engine in the presence and also remotely, has confirmed, that HPFP is a very safe hub. I had one HPFP of the N43 series engine, pressure regulation valve of which was pledged (more detailed description will follow), also several suspicious cases in remote diagnostics. Suspicious, because I haven’t got complete confirmation of HPFP problems. In the same time I know, that for several hundreds of diagnoses engines HPFP has been replaced, and as you can already guess, the problems haven’t disappeared after replacement of HPFP and injectors. The owners of the cars turned to me for help. Basic problems – CCVV; NOx system; some leaking injector – nothing, which would be connected to HPFP problems.
But now – for everything in a row. In the beginning: I will let me copy material of BMW AG, who corresponds to structure of HPFP of N53/N54/N55 series engines and also a short description of its performance.
Nuances, to which is worth to pay attention:
- the engine will perform normally also in limp mode with turned off (or completely damaged) HPFP. If HPFP is turned off, in the moment of start (data for the engine at temperature around 20 .. 30 oC) DME will increase the opening of the injectors from 0.4 .. 0.5 ms to 15 .. 20 ms (it means, according to the pressure of 5000 hPa – such pressure will be provided by LPFP). So: the rail pressure will be around 40 times less than in normal mode, but the opening time of injectors – around 40 times longer. As a result, the amount of injected fuel will be correct. Accordingly – if the engine is not able to start or it stops, HPFP is not the damaged hub! LPFP have to test; if it supplies the required fuel pressure (even in wide range: around 4000 .. 6000 hPa), the engine doesn’t lack the fuel – you have to look for a problem in other places! In such mode (with 40 times longer injector openings) the engine is able to perform quite normally – you will be able to reach the repair shop or home!
- As already mentioned in the entry about hydro blow, if HPFP detects abnormally high fuel consumption (obviously, some injectors has stayed in opened condition), HPFP is turned off, to spare CO catalytic converters and Lambda probes, and also avoid unnecessary consumption of fuel. Reducing the pressure for 40 times, the amount of leakage also reduces for 40 times – no hydro blow or other significant problems are possible.
- DME can turn off HPFP in the moment of start not only in “classical” (mentioned before in BMW AG materials) cases but also, for example, if in the moment of start several cycles one after another the fuel ignition is not detected. So, don’t be surprised, if, while testing the engine with, for example, disconnected injectors or spark plugs, that the rail pressure is only around 5000 hPa;
- for N43/N53 series engines, HPFP tries to maintain pressure in idle for at least 150.000 hPa; above 1500 RPM the pressure will reach and will be maintained for 200.000 hPa.
Continues – about most typical causes, why mistakenly (unjustifiedly) the HPFP is replaced
1. The error messages regarding lowered rail (HPFP) pressure: 2FDA; 2FCA.
2FCA fuel high pressure Upon release of the injection
2FDA fuel high pressure At or after the release of the injection
These error messages are recorded, if, when the engine reaches 200 RPM or more, the required pressure is not reached with a closed regulation valve with a max flow rate of the pump (PWM of valve close to 100 %).
Theoretically, these error messages can point to:
- increased wear of pump’s plunger(s) – fuel leak along the plunger(s);
- leakage in pressure back-valve.
Unfortunately, typically (with a probability of 99 % of cases) the true causes are:
- bad condition of a battery, starter, power wiring – the engine struggles (with breaks) to reach necessary RPM, and these error messages are recorded (directly) in the moment of starting the engine;
- leaking injector(s);
- unstable fuel supply pressure of LPFP, sometimes even air in the fuel system (due to leakages in back-valve of LPFP system and/or in fuel regulation valve).
As you understand from the description, the error message 2FCA is recorded between intervals of injector opening. So, with (theoretically) closed injectors HPFP was not able to reach the required pressure. In turn, the error message 2FDA is recorded, if the pressure drops at the moment when the injectors are open.
If these error messages are recorded, in the freeze frame of error messages check the conditions, when they were recorded – quite often they are recorded by significantly lowered RPM. It’s clear, that by 200 .. 300 RPM the flowrate of HPFP is very small, accordingly – it will have problems to maintain the required pressure. In such cases, you have to be aware, if and when the engine has totally stopped, or (at least by readings of odometer) be aware regarding the problem in the moment of start (a problem of starter – reduced RPM).
Both error messages, mentioned before, indicate lowered pressure in specific conditions, not the defect of the pump!
2. The error messages regarding plausibility: 29F1.
29F1 fuel pressure, plausibility
This error message is recorded in case if three basic parameters of rail system don’t match:
- pressure, developed by a pump;
- PWM supplied to pressure valve;
- fuel consumption.
Or, speaking simply – it didn’t succeed to maintain the pressure of the pump in necessary range, because the PWM, supplied to pressure valve, was “incorrect” (inappropriate to a range of pressure valve adaptations and management maps).
Here we have to keep in mind, that HPFP is a mechanical element, which is made from hard materials. Plausibility points to discrepancies, appeared swiftly – such swift (!) discrepancies cannot appear in the case, for example, due to wear of the pump, because the wear creates slowly! Slow changes in performance of HPFP, instead, are compensated by its adaptations.
A typical cause of this error message – short-term (but significant) differences of LPFP pressure from ideal (5000 hPa); short-term problems of leaking injectors. Taking in account, that LPFP is a “simple” DC motor, for at least half of cars I inspected had problems in its performance – fuel pressure of LPFP contour was significantly more unstable as it’s supposed to be (5000 +/-30 hPa). Very often (at least in History memory list, even, if the list of actual error messages has been recently deleted) the error messages regarding LPFP could be found, but nobody has taken it seriously.
In parallel to this error message also the error messages regarding disconnecting some cylinder (due to group misfires), or regarding LPFP – cause of the problem should be looked for in these directions.
If parallel the error messages regarding fuel mixture are recorded, check the rail pressure sensor – incorrect indications of it can be the cause for error message 29F1.
3. The error message regarding rail pressure (static): 29F2
29F2 fuel high-pressure system, fuel pressure
This error message is recorded, if for time X (several seconds), not taking in account “incorrect” PWM of the pressure regulating valve (it means, using all available resources), it hasn’t succeeded the necessary pressure. This error message is quite rare. If the error message 29F2 is recorded, definitely check the freeze frame of the error message.
Possible (typical) causes:
- for some reason the engine was close to shutting down or even had stopped (in attributes, abnormally low RPM will be fixed – below 600);
- check, if parallelly any other error message regarding turning off some of the cylinders is present – the cause of such error message can be opened injector;
- check, if error messages regarding LPFP are present, and even if they are not, check the stability of the LPFP system;
- check, if the error messages regarding misfires due to lowered fuel level. The argument “till 0 there were still 2 sections” has to be ignored, because the indicator of KOMBI can “lie”, also the fuel can rush in the tank while starting the swift movement or braking suddenly. If the error message regarding lowered fuel level is recorded, LPFP management module EKP has detected “dry” mode of the pump – this is a indisputable proof, that there was not enough fuel.
If parallel the error messages regarding fuel mixture are recorded – check the indications of the rail pressure sensor (their conformity to control manometer).
4. The error messages regard plausibility: 2AAF; pressure (static) 2AAE.
2AAE fuel pump, pressure
2AAF fuel pump, plausibility
Both these error messages refer to LPFP (not HPFP)! Unfortunately, very often, when these error messages are detected, “specialists” start exactly with HPFP. LPFP is located in the fuel tank, it supplies fuel to HPFP (that’s, why it’s performance, is so important).
5. Specific cases.
In a single case, when I “caught” damaged HPFP of the N43 series engine, the following error message was recorded:
2FBD fuel pressure steuer ventil, plausibility
When starting the engine (it’s idle was very unstable), I stated, that:
- the pressure of HPFP is correct (close to 5000 hPa);
- rail pressure is increased (very close to the max mark: 250’000 hPa);
- integrators are by the mark of -30 %; Lambda around 0.80 (so, even by fuel correction of -30 %, the fuel mixture still is very rich).
After a moment, the error message regarding rail pressure sensor indication was recorded:
29E2 fuel injection rail, pressure sensor signal
Obviously, the HPFP pressure regulation valve has been stuck in closed position, pressure exceeded max measurements, which sensor can recognize: 250’000 hPa. Taking into account, that the pressure regulation valve of HPFP for the N43 series engine cannot be disassembled or repaired, due to its defect the full HPFP has to be replaced. Replacement of HPFP solved the problem,
As we see, the error message 2FDA was recorded in certain circumstances:
- the engine has been just started (mode 1: open loop fuel correction);
- the engine has reached 1500 RPM;
- the engine has been turned off for more than 4 hours;
- reached pressure is around 120.000 hPa (instead of at least 150.000 hPa).
Taking into account long standstill time, the fuel backflow is possible (due to leakages in LPFP, some leaking injector).
The error message regarding rail pressure recorded in the following circumstances – pressure regulator valve is closed (PWM is 99.6 %), not taking into account, that:
- rail pressure is as if reduced: around 61.000 hPa (instead of necessary 150 .. 200.000 hPa);
- but the fuel mixture data display indicators -30 % for both banks: obviously, the rue rail pressure is significantly higher.
In this situation – check the rail pressure sensor, it’s connections. It is obvious – it indicates incorrect pressure.
Attention: the error messages regarding fuel system (both for LPFP contour and rail system) can be the cause, why DME works in conditions of limited functionality! Following operations can be stopped: an evening of cylinders efficiency, a creation of LTFT (in harder case) or even usage of existing LTFT! After solving fuel supply problems, the engine has to be re-adapted!
Viewing Live data:
LPFP and HPFP pressures can be seen here: ../F5/F2/F6
HPFP pump test module:../F6/F2/F6
More about performance nuances of both pumps read here.
At the end (summary):
- as already mentioned before, HPFP cannot be the cause, why the car is not able to start; it shuts down, or it can not drive (yes, with reduced power, but relatively normally);
- HPFP (except cases, when the rail pressure sensor indicates completely incorrect rail pressure values, but DME is not able to eliminate this problem – obviously, the pressure valve is damaged) will not be the one to blame in case of short-term uneven performance of the engine. Additionally, the defect of the pressure regulation valve is a very rare defect;
- if the error messages regarding rail pressure problems are recorded, in 99 % of cases the leaking injectors are ones to blame, also problems with LPFP (its pressure, jittering) or pressure sensors (less often);
- if the error messages regarding maintaining the fuel pressure are recorded, the engine can perform unsatisfactory, because part or even all its adaptations, which refer to fuel mixture, can be switched off. When DME “see’s”, that there are problems with one of main (in this case – fuel pressure) parameters, “don’t trusts” the received information. After eliminating the problem, the engine has to be re-adapted, only then DME will restore full functionality mode.