Fuel pressure regulator

You will say – what value can be found in this entry if the topic is a very simple element – regulator of fuel pressure?

I think you find some surprising information!


Fuel pressure (mechanical) regulators are used, starting from first electronic fuel injection concepts (for example, LE-Jetronic, M20 series engines), continuing with M20/20/60 even till first N series engines.

Using a mechanical fuel pressure regulator, fuel transmission concept works in the following way:

  • fuel pump (it’s connected to the +12V supply for all the time) pumps the fuel with max power to engine partition;
  • fuel reaches injectors (rail), leftover is redirected back to the fuel tank;
  • back-flowing fuel is used to pump the fuel to “second/correct” side – the side, where the fuel pump is located.


First surprise: fuel pressure regulator may have (and used by BMW – usually has) THREE outlets! And all of them are participating in fuel pressure regulation!

Second surprise: fuel pressure regulator (two-cameras type) maintains a constant pressure between both cameras, it means, upper and middle outlet! So, when measuring the fuel pressure in rail, which is maintained by fuel pressure regulator, we CANNOT talk about fixed pressure, if we don’t know (don’t take in account) the pressure of upper camera and upper inlet!


Third surprise: when we talk about pressure, which has to be stabilized by a fuel (two-cameras type) pressure regulator, we have to know, by what conditions it is defined! These conditions are mentioned in the datasheet of the exact regulator. There can be several scenarios – the pressure is defined between cameras; maintained pressure, if in the “upper” camera has pressure (depression) X, etc. As you understand – if we don’t know the conditions – the real pressure can differ for 1 bar (if the pressure of “upper” camera changes by 0 .. 1 bar).

For example, if the upper outlet is not connected anywhere (pressure in it – atmosphere pressure: 1 bar), pressure, maintained by fuel pressure regulator, will be for 0.8 bar higher than in case, if the “upper” camera will be connected to the inlet manifold with pressure 0.2 bar in it (the engine runs idle, Homogeneous mode, without using Valvetronic).


Fourth surprise: two different scenarios are possible for use of “upper” camera:

  • in older engines, the pressure regulator was placed at the end of the fuel rail, “upper” camera – connected to the inlet manifold;
  • in newer concepts – fuel pressure regulator is placed by the fuel pump, below the floor; “upper” camera connected BEFORE throttle.

The old concept ensured automatic compensation of inlet collector depression – fuel in rail all the time was for X bar higher against the environment, where the injectors were injecting. This method ensured unchanged flow rate of the injectors.

But, this method has one deficiency: a rapidly opening throttle valve (in the moment, when we want to start quickly), depression in inlet manifold decreases rapidly. Accordingly, the pressure on rail has to be increased rapidly for around 0.8 bar, moreover, the requested fuel amount also increases rapidly. This situation is not favorable – very high possibility of fuel pressure problems (shortage of fuel), additionally – short term fuel inadequacy of fuel pressure, when the driving conditions are changing rapidly.

In newest solution this problem is solved – fuel pump maintains unchanged pressure in rail all the time, independently of depression in the inlet manifold. Depression in the inlet manifold is calculated by DME (the microprocessors, used in DME, are powerful enough).

In this concept the “upper” camera compensates the following parameters:

  • changes in atmospheric pressure (for example, in mountain areas);
  • changes in air filter permittance.



Checking the pressure, which is maintained by a pressure regulator, it is obligatory to check the performance of both cameras! Evaluate the performance of pressure regulator – it’s ability to compensate depression of the inlet manifold (if the regulator is placed at the end of rail) of air filter permittance (if the regulator is placed by the fuel pump). And we have to remember – we have to clarify conditions, by which the parameters of the current pressure regulator are measured.



Fuel pressure regulator, BMW p/n  13531436110, used on M50; M52; S50 series engines.