I have looked on every corner of the internet, read every forum, and searched ever diagram to try and resolve my issues and have not come up with a definitive answer.
I have been running into an issue where randomly, with no rhyme or reason, my fuel pressure drops from around 1100 psi to around 350 psi during deceleration then will jump back up. If it sits low for long enough it gives me a 2c01 code, low High-Pressure Fuel Plausibility: Pressure Too Low. At first I thought maybe a bad fuel filter, then maybe faulty fuel pressure sensor, or maybe a problem with the solder for the fuel pump relay on the JBE. Unfortunately nothing has resolved it. When the fule pressure drops if i blip the gas it jumps back to normal like nothing happened.
I know there is a 12v constant that runs from the fuel pump, to the oil pressure solenoid, both O2 sensors, thermostat coolant sensor, as well as the turbo coolant pump. I'm not sure if this issues is something potentially related to wiring as randomly my oil pressure solenoid seems to not activate and gives a somewhat low oil pressure, it generally fixes itself if I shut of the car and start it again.
Any help trying to diagnose this would be greatly appreciated as my primary car was totaled when someone decided to rear end the crap out of me.

 

What year is your car? It not unheard of for the early N18 engines to have high pressure fuel pump issues like the N14 engines. (They use the same fuel pump). A build date of ~3/2012 was the changeover to the newer, slightly more reliable high pressure fuel pump design.

 

It's a 2011 Clubman N18 S, its the old style pump. I'm not completely against the idea of it being the hpfp, just don't wanna spend that much money if it isn't going to fix it. From other articles of people describing there issues it didn't seem like a hpfp to me.

 

Can you give more details about what you have done so far?
What scan tool are you using?

You are spot on to consider both an electrical and fuel problem. Gathering diagnostic information to differentiate the two is key here.

 

Low fuel pressure is cause by a fueling issue. If the DME is seeing good fuel pressure readings from the fuel rail sensor, it is something in the fuel delivery system. If you've replaced the low pressure pump and fuel filter, then the last component is the high pressure pump.

If the oil pressure and fuel pressure drop at the same time, then its a power or ground issue.

 

I've read the codes with a obd scanner designed for bmw/mini as well as using ISTA. So far I've only replaced fuel filter, replaced fuel pressure sensor, the O2 sensors would replaced a little while back. I'm leaning towards maybe electrical as the downstream O2 sensors voltage seems to be reading a bit funky while deceleration and acceleration.

I verified that the 12v is good while in accessory mode, but can really check it too well while car is running/driving.

 

It isn't exactly at the same time together but one starts acting up then the other one starts having problems, while the downstream O2 voltage is a little all over the place.

 

Does your obd scanner read and/or graph live data?

 

My bmw/mini scanner will read live date, I also have TorquePro which will give me small graphs of the data. What specific values are you thinking I should look at?

 

Can any of the pressure or voltage issues be reproduced while running the engine but not driving?

 

Im not sure I havent tried. Sometimes, after I notice the fuel pressure dropping or it pings the 2c01 code. If I shut off the car and start it again the oil pressure will drop low. But the fule pressure will return to normal.

 

Have you ever driven the car with your laptop connected to ISTA and commanded to record specific live data?

 

No, I can though. I haven't dived super deep into all ista can do but if you have suggestions on what to record I can.

 

I don't have experience using ISTA, but fortunately you do. I queried Google Gemini AI for ISTA instructions on how to record the relevant live data. Please see attached PDF for Gemini instructions. I hope this helps.

 

I can take a look later see what sensor values I can get. Hopefully it'll point me in the right direction to find if it is an electrical issue or actually the hpfp.

 

Good luck!

The ISTA live data results (Rail pressure setpoint, Rail pressure actual, Fuel high-pressure control valve Duty Cycle/PWM, Terminal 87 Voltage, oxygen sensor downstream of catalytic converter voltage) should point you in the right diagnostic direction.

 

Thank you I'll update with what results are, today or tomorrow.

 

So currently having some problems with my cable for ISTA, should be getting a new one today. I did get some logs from TorquePro that shows the Fule pressure PSI, engine rpm, and O2 downstream voltage. I compiled into an excel file with 2 charts with graphs. If you could just glance and it and tell me what you think, it seems really weird to me that my O2 voltage and Fuel Pressure both drop a lot. The voltage for O2 seems to be like all over the place.

 

Your data are more consistent with an electrical issue than an HPFP issue.

Focus first on a possible wire harness issue.

Inspect the wire harness that runs behind the engine and behind the vacuum pump. The issue could be oil contamination or wire damage. For the former, the oil pressure solenoid seal can fail, allowing oil to wick into the wires and travel all the way to the DME. So also inspect the two large 53-pin DME connectors for signs of oil.

 

Alright thank you, I will take a look when I can later tonight. I will also try running ista with the specific values and terminals you mentioned as well. When I recent had it apart to replace the fuel pressure sensor I did not notice anything major, although I did see a light tear in the insulation in the 12v for down stream but did not seem like it would cause this issue but potentially could.

 

Definitely worth looking into.

 

Can TorquePro monitor "Control Module Voltage"? If so, repeat your test by substituting the downstream O2 sensor signal voltage with Control Module Voltage.

Of course, if you get a working ISTA cable, the ISTA tests would be an even higher priority.

 

In the data tab with all the values I do have voltage for control module v but idk what exact module its coming from if it is the dme or like the footwell module

 

In essence, the control module voltage is equivalent to the voltage supplied to the DME by the Main Relay (terminal 87). Terminal 87 is more relevant to your issue than the downstream O2 sensor signal voltage because the Main Relay supplies voltage to the O2 sensor heaters (circuit source for code 2c01).

 

Looking at the data it looks like the voltage for whatever control module it is looking at does decrease with rpm, but when the fuel pressure drops the voltage drops by like .2 ish