I have been troubleshooting an issue with my fuel rail pressure sensor on my 2012 MCS. I bought the car a few months ago and despite having a CEL for random missfire it was running fairly well so I figured it needed a turneup. I replaced the spark plugs, ignition coils, and fuel injectors. After that the car would not start and I read some where that if the car starts with the fuel rail pressure sensor disconnected then the fuel rail sensor is bad. So I then disconnected the sensor and the car fired right up but was running in reduced power with the RPM limited to about 4K, which also prevented the turbo from kicking in. I received a CEL for P0193 (all others cleared) which indicated the fuel pressure was high/sensor failed high. After several weeks finally tracking down the correct sensor replacement, I replaced it and got the same issue. By this time, I replaced the fuel filter, low pressure supply fuel hose to the HPFP as well as the HPFP (new bosch unit from RockAuto).

For troubleshooting, I placed the key in and with it on, I checked the wiring for the sensor connector and found the three wires were 5v, 0V, and 5v. Someone in another forum said the sensor wire should be 0.6v with the car on so I suspected a short of the reference and supply wires. I then disconnected the associated wiring harness bundle from the ECU and read 5V on both A22 and A24 terminals (corresponding to the sensor signal and reference lines). I am at a loss now and ready to take it to someone else that can figure this out as it eats up my weekends and kills my bad back leaning over the engine. I don't want to risk causing further issues with the car and not being able to figure out what's wrong with it.
The only way the car runs is with the fuel rail pressure sensor electrically disconnected.

Any thoughts/recommendations?

 

Well I would say first thing, What is the "real pressure"? What is the pressure of the fuel at the rail? What is the pressure of the fuel being delivered by the low pressure fuel pump? How long will it hold those pressures in both places?

It seems to me you need to step back to the basics first. You are replacing all kinds of things in a guess-wise fashion. I find that works sometimes if it is a "single layer problem". In other words, you suspect X, X is cheap, you replace X, viola problem solved. However, if that is not the case, you can't just start replacing everything. You need to work the problem. Why are you replacing fuel lines unless they are leaking and not holding pressure? Do they just look bad and need to be replaced anyways? That is a fine answer, but don't expect it to fix anything. I've seen plenty of things on a car that look like they should have been replaced years ago, go on and work for another 5 years just fine.

 

mini-is-for-me, thank you for your time and effort in responding. Your questions and comments were valid. Initially, I felt it wasn’t very helpful for my issue because I had already went through all of that but after realizing I should have been more detailed so that anyone else facing similar issues may find my details useful.

Here are the details leading up to my issue. When I got the car it needed some attention. A CEL with the following codes were present: P071, P0300, P0302, P0303, P0304, P119D, P10ED, P10EE, and P053A. The oil and air filter were very dirty. The valve cover was leaking and needed a gasket replacement. While replacing the gasket I inspected and replaced the ignition coils and spark plugs. The plugs were worn and the gap was inconsistent. The coils appeared fine but I didn’t want to swap coils back and forth trying to determine which, if any, were faulty so I replaced them as a set.

Since I had pulled the intake manifold and had a lot of room, I removed and inspected the fuel rail and injectors. The injectors were very dirty and potentially clogged. Although, not necessarily an issue, one injector was a different brand so I chose to replace all of the injectors. After replacing the valve cover gasket, I replaced the intake manifold gaskets and changed the oil and air filter. I also cleaned the air flow sensor.

After everything was put back together, I cleared the CEL and attempted to start the car. Unfortunately, it would not start and run. I received a new CEL with the code P0193 which indicated an issue with the fuel rail pressure sensor. Possible causes of the code were a faulty pressure sensor, faulty in-tank fuel pump, dirty fuel filter, clog in fuel line, faulty High Pressure Fuel Pump (HPFP), or a wiring issue. A quick look at the fuel rail pressure using my BlueDriver diagnostic app showed ~ 3600 psi which is well over the normal operating range. When doing the previous work I did disconnect the fuel pressure sensor connector to be able to move the wiring harness out of the way and thought I may have damaged the wiring so I removed the air ducting and intake manifold again. I checked the connector and wiring but did not see any issue at the time. During my research I found that if the sensor is disconnected and the car can start, then the sensor is faulty. In my case the car did start with the sensor disconnected so I ordered a new sensor.

Upon installing a new pressure sensor, I cleared the CEL and attempted to start the car but it would not start unless I left it disconnected. Once again I got the same P0193 code. I then checked the low pressure fuel supply hose. It appeared to have been removed previously and was worn on the connections and had some significant abrasions along the length of the hose so I installed a fuel pressure gage inline and tested the fuel pressure. Pressure was ~ 68 psi and went down to about 63 psi over the course of 10 min. I then inspected the fuel filter. It was noticeably dirty so I replaced it. The tank looked clean with no visible debris. In hindsight, I probably should have completely drained the tank and wiped it clean. Maybe next time. I did consider the in-take fuel pump being the issue but felt it wasn’t likely, since the engine starts and idles fine. After priming the fuel lines I attempted to start the car but got the same code. I considered the HPFP as the issue so ordered and replaced it but that wasn’t it either. I suppose I may have received a faulty pressure sensor or HPFP but I can’t know for sure. After more research I checked the pressure sensor wiring again. Readings on both the supply and sensor wires indicated 5V which I suspected the sensor wire was shorted to the supply or another 5V line. With the wiring harness removed, the ECU connection indicated 5V on both pins (A22 and A24). To me, the wiring between the sensor and the ECU checked out fine. I did not expect to see 5V on the ECU pin for the sensor line (A24). That’s where I have been stuck for the last week.

This is the only mini that I have ever owned or even driven. In over 28 years of owning and maintaining 25+ vehicles this is the first time I have encountered such an issue.

 

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Yesterday, I replaced the FRPS and reinstalled my engine harness after previously removed to check continuity on all pins. Once again, car starts and idles fine but has the same code of P0193 and is limited in power. Just for comparison, I partially installed the spare harness (PN 12518605260) I got from eBay and I get the same readings on the FRPS wiring harness connector.

I’ve been working on this car for several months trying to figure this out but back to square one. I’ve replaced the fuel filter, checked the LPFP pressure, replaced the HPFP, replaced the FRPS, had the BMW “specialists” diagnose a “bad” ECU (I think they caused it), cloned and replaced the ECU, checked the wiring harness, and replaced the FRPS again.

Does anyone out there know why my FRPS connector has 5v on the sensed line? Anyone seen wiring discrepancies with the Bentley Manual schematics or those on the newtis.info website? I live in Guam and we have limited service shops and replacement parts takes 2-3 weeks to get. I’d love to get his car I running right but so far it’s been running me ragged.

 

A Little Late... I was checking about replacing my fuel rail pressure sensor on my Mini and read your post, saw you were on Guam and had to reach out, 'cos I'm on Guam too! How'd it work out? I was going to recommend a place and saw that it's so long ago... Wondering if you're still here, or did you go off island already?