Hi all,

I'm chasing a P0171 system lean code and checking the fuel pressure on 2005 MCS. I don't quite understand the results or know if they are normal.

- Key on - pressure quickly climbs to 52-56 psi. If I turn the key off and on a couple times it will climb as high as 62.
- Start engine and idle - pressure drops to 41-42 psi.
- Mash pedal and rev engine - pressure climbs to 54-56 with pedal down, drops to 38 when I let off the pedal and the engine is winding down, then settles at 41-42 again.
- Hold engine at high rpm, 5-6000 - pressure runs about 39 psi.

Total range is 38-62 psi, all tests done parked in neutral. Bentley manual simply says hook it up, start it, and it should read 51+-4. I found seemingly knowledgeable input on another forum that says key on - 52, idle - 42, which is about what I'm getting.

So, fellow Mini techies, is this normal?

Thank you, Jeremy

 

Seems about normal.
Mine reads about the same.
Since our fuel systems are regulated by vacuum/boost, if you also have a boost gauge you can see the pattern.
But if it's not a massive vacuum leak, everything will be close enough to normal it will be hard to tell.
Are you just getting your code at WOT? This can be a sign of a slight leak.

 

Weird that the Bentley manual seems inaccurate in this regard??? But it definitely seemes as if it was SUPPOSED to do what it did, and what you say makes sense about it's being regulated according to vacuum, which disappears when you floor it.

Code comes and goes at seemingly random times. I'm gonna start another thread about it. Thanks!

Jeremy

 

Possibly the Bentley is giving you pressure off the pump itself, should be 60+.
If you test anywhere prior to the fuel rail you'll get the Full and constant reading of 60+, if you test off the fuel rail, you'll get the regulated amount.
(A few of us discovered this by comparing different tap in positions for fuel pressure gauges)

 

OK, that's why I'm getting 60+ before the engine starts. Thx again.

 

Hi all, does anyone know what the maximum rail pressure for an R53 should be - i.e. pressure at high revs (flow) and max boost?

Is it 3.5Bar (Regulator) + 11-17psi Boost = 62 - 67psi?

To clarify:
Standard R53 11psi boost = 62psi max.
Tuned at 17psi boost = 67psi max.

Or is it 65psi - as the filter bucket has a 4.5Bar regulator controlling pressure up to the rail regulator and could limit the system / rail pressure to 4.5 Bar or 65psi meaning the fuel system can only compensate for 1 Bar of boost.

Has anyone changed the filter bucket regulator, modded it or had issues with it e.g low system pressure causing low rail pressure?