[DarrenR56]

Hi all I'm new to the forum.

I (my other half) have a R56 Cooper S and as many of you may expect have been having some fueling issues.

At idle the fuel pressure was sitting between 650-750 psi and since it's getting cold again I thought I'd better change the HPFP.

After changing the HPFP 2 weeks ago with a genuine item from Neo Bros it idles and drives better, but occasionally the idle gets rough again and the fuel pressure is dipping to the same kind of range.

What's the next port of call? In tank pump?

I don't really have facilities to test it properly as outlined on pelican but it's the only thing I could think it would be.

 

[DarrenR56]

in tank pump should always be replaced with the high pressure pump in a perfect world, low pressure or intermittent low pressure in tank pump will hurt the high pressure pump as it needs set flow and pressure to keep cool and lubricate,,
also have seen people change the high pressure pump and to find later the timing chain slips teeth or top guide snaps off to then realise it was a chain issue and the cars ecu was just trimming fuel demand to suit how far out the timing is, even main dealers have done this,, i always on [prince engine tell customer the first place we need to check is timing chain get that right then you know the systems are where they are meant to be,
when chain tensioner comes to end of travel and the car comes off load fast the back lash in the drive line will reverse the load on the timing chain on a good tensioner it wont allow the timing t alter but when its weak it will so on some cars its a warning when the idle drops then once the tensioner catches up it goes back right again, also when the engine is under load up the rev band this holds the engine in time when take foot off it goes the other way

Luckily I had the chain done last year so I can rule that out, it's a late 2010 N18 model with 45k on the clock so I think the tensioner was gunked up which allowed the chain to stretch a touch.

Is it part no. 16112755082 I would be looking for? I see Neo Bros have it for £132

 

[DarrenR56]

should be ok then yep think the neo bros green top one should fit bit always ask them first with reg number, neo bros are really good on mini parts i try and use them when ever i can good parts and service, might be worth you draining off some petrol from the tank when the sender is out and check for water in fuel have seen cars that have had a bad batch of fuel hurt the pumps before i always try and think of worst case and other stuff that could start a train of events to why something has failed etc, bmw now do the parts only timing chain kit with new chain, new latest tensioner. guides bottom sprocket and bolts for £230 from ocean bmw plymouth and a tad less for trade customers all the latest ones think they are on the 3rd update of it all and still use the same chain lol

Strange thing is the car drives really nicely, there a little jolt now and again coming off the gas strangely but that's about it drive ability wise. The fuel pressure is the only thing that sticks out to me on idle...

Is the fuel filter still under the seat on N18s? there's a guide on Pelican but it only seems to be 2007-2011 models (pre-LCI)

 

[DarrenR56]

i would question is it the pump or is it what the ecu sees on the 02 sensors and fuelling trims very common for them with past chain issues to sometime soon after need upstream 02 sensor or and cat on higher mileage ones, best way to find out on fuel filter is to follow pipes back to rear of car for filter housing i believe its same as strainer filter only,, surprised no one has come up with a filter with a water trap in it to be honest as what ever is in fuel just gets pumped to the pump,and the pump blades work on a few microns of tolerance to keep high pressure up dont take much to destroy them ans water being the worst,,

What would I be looking for on the fuel trims to see if it was an O2 sensor issue? I can monitor this using the Torque Pro app which is what I use to read codes and monitor coolant temps/fuel rain pressure

 

[DarrenR56]

below screen shot of n18 02 sensor readings at what temp etc on a perfect engine the upstream will always move around more than downstream sensors if both move at same time then cat is dead, ie either have voltage on zero then faulty or wiring is, if the voltages on signal 5v ref wire is above 1,1volts same again something is making mixture wrong air leak maybe or the other way fuel issue ie injectors leaking off after cycle and bare in mind the injections times are pulsed by the ecu so that makes any leaking ones a lot worse over fuel to the amount of air charge, the map/maf temp sensor and 02 sensors govern the amounts and when fuels and controlled by the central parts of ecu programming ie reads all these sensors and works out how much and when to spray fuel also how much boost on turbo cars

Mike, the car passed it's MOT emission with flying colors just a few months ago, would this be a good indication that the O2 sensor is ok?

I seem to remember fuel trims varying between 0-2%ish but I'll check again later.

 

[DarrenR56]

Just a quick update...

got a sender pump and went to change it, can had half a tank of petrol and when I opened the cover it was virtually still full! I'll need to reattempt when I've got more daylight and the tank has run down more. Is there any reason not to change the pump when the tank is on 2-3 bars on the gauge?

I had great difficulty getting the O-Ring back on and was definitely feeling the effects of the fuel vapor