Hi all! I've been a long-time lurker here and gained information from this site for years - thanks all for your help!

We've got a 2007 R56 Mini Cooper S (N14 engine) with 140k km on the clock. About 12 months ago the car developed cold start issues. A local garage messed us around with ECU error codes and eventually convinced us to replace the entire ECU at a ridiculous cost, but the cold start issues prevailed, so I took things into my own hands.

I diagnosed our issues as fuel pressure related (thanks to all the information on this site), and bought a genuine OEM (Citroen/Peugeot) HPFP. I installed this last week, and the car was instantly transformed! Started perfectly each time and ran very smooth with no issues. Great!

But two days ago the car suddenly started coughing while my wife was driving it, and yesterday it died completely while she was on the way to work.
Today I connected my OBD scanner, started the Torque app and drove around for a while to diagnose the problem.
Idle: ~730 PSI
Under load: much higher, several thousand PSI
The car drove fine, but as I pushed the car harder during acceleration I began noticing dips in fuel pressure, and the car "coughing"/jerking accordingly.
After one final full throttle acceleration the fuel pressure dropped right down to ~120 PSI, at which I could limp home but it refused to accelerate at more than 10% throttle.

Car was parked for one hour. Upon restart it was choppy but fuel pressure read ~730PSI. Drove it a few minutes and after the first real acceleration attempt the fuel pressure dropped back down to ~120PSI - is this limp mode maybe?

Read the error codes and they are:
P0001 - Powertrain
P0300 - Powertrain: Random/Multiple Cylinder Misfire Detected
P0301 - Powertrain: Cylinder 1 Misfire Detected
P0304 - Powertrain: Cylinder 4 Misfire Detected
P2177 - Powertrain: System Too Lean Off Idle bank1

So, my question: has my brand new OEM HPFP failed within a week, or could this be perhaps the in-tank pump, or some other issue? I have a fuel pressure test kit but not the right fittings for the Mini fuel lines, so I haven't been able to test the in-tank fuel pump pressure.

Thanks for any input!

EDIT: I had a fuel filter lying around so I replaced that. It did not fix the problem. Car started well again and fuel pressure was around 700PSI. Drove well until pushed hard and then fell to 120PSI (which might be limp mode, I don't know).

EDIT 2: Dug around in some receipts and should mention that the following items were replaced about 18 months ago:
Cam chain
Cam chain tensioner
Spark plugs
Ignition coils

Currently contemplating whether this is carbon build-up or ignition system.

 

I've done a lot of reading in the past few months and based on your mileage alone I'd consider carbon build-up as a distinct possibility. The carbon buildup can cause misfires. I was getting the P2177 for about a week but I ran several bottles of fuel injector cleaner and this one has gone away.

 

You can't remove carbon buildup with additives. You need walnut blasting (if that should be the root cause).

 

I've spent the day on the car. Today I haven't been able to start it successfully once, which has never been the case before. Fuel pressure is at ~120PSI before starting, might jump up to 300+ PSI while cranking but always drops back to ~120PSI. Is the car in limp mode, or should I be diagnosing the fuel system now?

Misfire only occurs on cylinders 1 and 4. I've swapped coils over between cylinders and result is the same, so coils are not at fault.
I took out all the spark plugs and made the following observations:
plug 1: Very sooty, with pieces of black on it (carbon deposits?). Wet.
plug 2: Very sooty, but a consistent coating without specks/pieces. Dry.
plug 3: As plug 2. Also dry.
plug 4: As plugs 2 and 3, but wet.

Currently I still suspect the fuel system. The fuel filter was so dirty when changed, that perhaps the new HPFP has pushed particles around the fuel system and caused a blockage.

Important questions:
1. Why is the fuel rail pressure only ~120PSI? (I have cleared the codes with my OBD2 reader, but it has not had any effect.)
2. Is there some connection between cylinders 1 and 4 that could explain this?
3. Could this still be carbon build up?

 

The easiest way to see if it's carbon build up (highly likely) given your mileage @ 140K approx 86K miles is to remove your intake manifold and take a peak with an inspection camera. Most of the shops who service Mini's with the N14 engine recommend a walnut blast to clean the intake valves. Here's a picture of one of mine at 87K. It's not a difficult job to get the intake manifold off. The biggest challenge the first time you do it is getting the 10mm bolt out and back in under the intake manifold that helps brace it. I can now get mine (10 mm bolt) in/out in less than two minutes but the first time I did it I spent 2 hours and a few good words. The way I learned how to do it is to use a magnetic nut driver on a 6" flex extension attached to a 6" extension with a small impact driver. You can reach the nut from the passenger side of the car after you take the wheel off. There's a space between the wheel liner that allows you to access the nut head. You'll need some good light to see the nut but once you do you shouldn't have any problems getting the intake manifold out. Every video I saw on YouTube talked about that one bolt being a big pain in the....

On the HPFP...did you replace the fuel line with the special coupling?

 

I have similar problems. My HPFP is acting up at 64K miles. I replaced my fuel filter and it was a mess. Black stuff and after it tried, it spells alot of like unrefined oil. The fuel that I got out of the fuel filter housing also was black with what looks like unrefined oil. So after I get the dealer service to replace my HPFP tomorrow, I'm going to drive my tank down to just 1-2 gallons, I'm going to siphon of the gas. Put a fresh gallon in the tank, drive it around the block hard, and siphon off that gallon as well. Then I will fill the tank with fresh high quality gasoline about half way with gas/fuel additive like Seafoam with fuel injection cleaner to try and emulsifier what is left and burn it out. I probably will try and run the fuel tank as low as possible and then fill it up from that point on.

I got my car used up in SD and I believe there were used cheap crap gas up there.

 

Thanks for the detailed description, that'll be really useful. Inspecting the intake valves is next on my list.

I did not replace either fuel line when replacing the HPFP. Is this known to cause any issues? I've been checking the system for leaks since the install and have not seen any.

Thanks, this gives me some ideas. We've always ran the car on 95/98 and always from one of two gas station chains who are reputable.
_________

After a night of sleep, my goal is to get the car back to 700PSI at fuel rail and go from there. I may re-install my old HPFP to see what change that makes... At least the car did actually start with that pump.

I think tackling the low fuel pressure issue before moving on to the misfire is a logical way to go. Ensure pre-conditions are correct before diagnosing operation.

 

What is the pressure coming off the low fuel pressure and will it hold that pressure for 15 mins? At 140K, it is also time for your low pressure fuel pump to start failing.

 

I can't figure out a way to measure the LPFP pressure. I bought a "complete" fuel pressure measurement kit but it doesn't have any fittings that will work with the Mini system. I suspect I'll need to purchase an additional fuel hose (the one from subframe to the HPFP) and modify the old one to add a T-junction for my kit.

How have other people here measured their LPFP pressure?

 

@2min
Also I have a Foxwell code tool that allows you to see what the ECU sees the pressure as and plot it over time. The ECU is already reading the pressure gauges it has built into the car without taping into anything.