So my Cooper S 2007 is having really weird symptoms that lead me to suspect something is wrong with the fuel delivery to the high pressure fuel pump (HPFP).

Can anyone help me with a good explanation of how the in-tank fuel system operates?

Mainly, how is the pressure regulated? It sits at a specified 72psi feeding the HPFP, but there is no return line from HPFP back to tank so there must be a pressure regulator somewhere.

I can see three elements of which I'm not entirely sure of the purpose.

1) On the fuel pump there is a spring at the top. It looks like it has a pattern for a Philips screwdriver but I think that is actually just folded tabs to locate the spring.

2) On the bottom of the fuel pump assembly (the sender unit) there is a rubber flappy valve.

3) On the fuel filter assembly there is some kind of diaphragm valve. ('A' in photo)

 

OH! And can anyone comment if it is normal that the fuel line pressure wobbles like this? The pressure gauge is hooked to the feed line on the HPFP and that needle is wobbling a bit, is it usual?

Video here: https://photos.app.goo.gl/Wx8re6ZPrZxTukpK9

 

What are your symptoms? N14 cars are really prone to HPFP issues. You may want to hook up a scan tool and check for fuel rail pressure while the engine is running.

 

I already replaced the HPFP and I'm working on ruling out other things. I just wanted to understand how the in tank fuel system operates so I can check for blockages or duff valves etc..

 

I wanted to follow up here. I took out the fuel pump and also the fuel filter housing to see how it all works.

The main thing I discovered is that the fuel pressure regulator for the low pressure side (before the high pressure pump) is part of the fuel filter housing, NOT the fuel pump. So if you have low fuel pressure from the tank feed, it may not help to change the in-tank pump, but rather the fuel filter housing.

This is not mentioned in any of the data I read on NewTIS, but after disassembling it, I can see how it works.

1) The fuel pump sucks fuel from the bottom of the left tank lobe past a one way flappy check valve.




2) Then it squirts fuel continuously over to the fuel filter housing in the right tank lobe.




3) The fuel passes through the filter and can exit along two paths. Path one is to the engine.



4) Second exit path is via the pressure regulator valve that opens and closes to maintain 72psi. When the valve open the fuel is sent out here.


5) The fuel passes through the blue thing, which siphons up fuel from the right tank lobe and returns it, along with the excess fuel from the filter housing, to the pump.



Here is the fuel pressure regulator. Unfortunately it is not listed as a replaceable item itself. It must be purchased along with the entire fuel filter housing and associated tubing.

 

Not sure if anyones done this, but I bet there’s a 5 bar bmw fuel pressure regulator out there that would fit, and you can buy that rather than the whole housing. Maybe not, but they do all operate the same way.

I’m in the same boat, hpfp replaced and I still get p02188 system too rich at idle

 

FYI... been referencing this thread for a project I am working on. There is a 5bar FPR used by BMW (found most commonly in the E46m3). There are 2 issues.. 1) It has a vacuum port, 2) the small "tip" that is shown in the last photo of the Mini regulator is larger in diameter than other BMW FPRs. You cannot swap. Small peg, big hole.