[redz06]

My 335i sedan with N55 engine occasionally goes into a reduced power mode and lodges fault codes P15DF, P0087, P0090 as well as various engine misfiring codes. Sometimes it shows the "Half Engine" warning light, other times not. Always, after I erase the fault codes, the engine runs normally, exhibiting boost and decent part throttle operation. Often, but not always, the lodging of codes and reduced power operation occurs just following a cold start.

Local BMW dealerships do not have a great reputation with me, so I have taken my BMW to two independent BMW shops in my area for diagnosis/repair. BMW parts are expensive, so one thing I wanted to avoid is just throwing parts at the problem. Both shops swore beforehand that they had excellent diagnostic capabilities beforehand and would not be throwing expensive parts at the problem.

The first shop claimed to use the same diagnostic software as the BMW dealerships use. The first shop charged me $165 and then admitted they could not pinpoint the issue, but recommended replacing the LPFP and regulator assemblies, since the HPFP had been replaced about 25k miles ago. Basically just throwing parts at it, since the LPFP and regulator were original, with 99k miles on them.

The second shop charged me $210 and admitted they could not pinpoint the issue. They recommended changing the HPFP and the HP rail pressure sensor, which sounded like throwing parts at the problem. Both shops said the LPFP and HPFP discharge pressures were normal. The second shop did run ISTA on my BMW to check the electric fuel pump, rail pressure sensor, and the HPFP and no faults were identified. ISTA did note that the test module does not include checks for load-dependent faults. ISTA said that if high pressure faults are encountered, the following fault causes may be present:

* obstruction due to fuel contamination
* damaged fuel lines

ISTA did also find the following fault which was lodged in DME memory: 002BEE - High Pressure Fuel, plausibility, cold start: Pressure too low.

I decided to take my BMW home and try to gather more data on the problem.
The next day I hooked up my OBDII reader to my BMW and did a cold start. Before the start the high pressure fuel rail pressure FRP) was 62 psi. After start, the FRP was only 75 psi and I hardly got out of the driveway before the half engine warning light appeared, so I turned around and went back to my garage. I shut the engine off and went into accessory mode so I could erase the codes. I then restarted the engine and the FRP went up to about 1300-1700 PSI until the idle went down to 727 RPM, where the FRP was 700 psi, on normal driving afterwards, there were no further codes and the FRP was 1300-1800 psi.

On the next day, I did another cold start and there were no codes and FRP was normal.

Another couple of days go by and I do another cold start, with normal FRPs. I drove the car 10 miles and stopped at a store. Did another start and no codes, normal FRPs. Then I decide to record data under full throttle starting around 3000 RPM. Here is my data recorded by my OBDII reader:

RPM Engine Load FRP
3133 22% 22 psi
3233 47 2078
3312 54 1933
3421 69 1722
3550 87 1395
3700 88 1408
3977 88 1358
4266 88 1222
4519 88 1105
4817 88 995
5510 67 1048
5530 24 75

At or near the last reading, the half engine warning appeared and a P0087 code lodged. I switched off the engine, erase the code and started the engine again without further codes and drove the BMW home gently.

I hope the presence of all of the data in one place will trigger more views and advice on how to address the root cause of the problem.

[lookalikehuuh]

Do you own INPA/ISTA or a BMW specific scan tool? I don't like OBDII readers as a main source of troubleshooting because they aren't able to read all the live data that a BMW specific scan tool or INPA/ISTA can.

So let's talk about your fuel pressures for a bit.

Low pressure fuel pressures should average around 72PSI, once the fuel pump/engine is running. It is normal to bleed off a little bit of pressure after the engine is shut off so starting at 62PSI Low pressure is normal.

High pressure pressures should be a few hundred PSI (maybe like 300-400PSI) with the engine off, as soon as you start the engine, idle pressures should climb and remain above 700PSI at all times. The moment you touch the accelerator pressures need to be above 1000PSI. When under heavy throttle/load you should expect to see 2000PSI+ the fact you are under 88% engine load and only seeing 1358PSI means either the HPFP is weak/dying or there is an issue with the signal being sent to the HPFP telling it to boost pressures.

I would recommend getting a log of a pull and post the information on datazap.me and give us the link. It will give us good information on what where we believe the issue could be. This will give us a graphical indication of throttle position, RPM, high and low fuel pressures, etc.

[redz06]

I am so sorry you do not like my OBDII reader, especially after I have spent $375 to fund independent BMW shops with better tools to diagnose my issue. And they have failed. As I have stated, high pressure rail pressure prior to start was 62 psi, not 300 or 400. If the engine starts normally, the FRP increases to around 1300 psi and this goes down to 700 psi at normal idle speed. On starting a full throttle push, the FRP increases to over 2000 psi for an instant, but cannot maintain that pressure as load and RPM increases.

I appreciate your recommendation of getting a log of a pull. Unfortunately, the shops that I paid my good money to did not do that or did not share that info with me. If other individuals or shops in the Houston area are willing to help out with this, I will endeavor to make my BMW available. Regardless, I believe the basic information you are seeking is already available in my post. Before you say throttle position, I can assure you my right foot was already on the floor.

[lookalikehuuh]

Originally Posted by redz06

I am so sorry you do not like my OBDII reader, especially after I have spent $375 to fund independent BMW shops with better tools to diagnose my issue. And they have failed. As I have stated, high pressure rail pressure prior to start was 62 psi, not 300 or 400. If the engine starts normally, the FRP increases to around 1300 psi and this goes down to 700 psi at normal idle speed. On starting a full throttle push, the FRP increases to over 2000 psi for an instant, but cannot maintain that pressure as load and RPM increases.

I appreciate your recommendation of getting a log of a pull. Unfortunately, the shops that I paid my good money to did not do that or did not share that info with me. If other individuals or shops in the Houston area are willing to help out with this, I will endeavor to make my BMW available. Regardless, I believe the basic information you are seeking is already available in my post. Before you say throttle position, I can assure you my right foot was already on the floor.

Its not that I don't like your OBDII tools, its just that OBDII tools don't have the ability to control any modules in the car (bidirectional communication) nor do they get access to BMW specific codes that can provide a huge amount of information. This is the reason I refuse to fund shops with better tools... the tools are only as good as the person willing to use them and put in the time to understand them properly. I personally have the prior version of this (non pro)
https://www.amazon.com/Autel-MK808BT...6-9d8efb903409

For the costs of the useless diagnostics from both of those shops you could have your own tool that has bidirectional communication and can access BMW (and most other manufactures for that matter) codes that can provide way more details. You can also turn systems like cooling fans, Evap valves, on and off plus tons of live data in 1 tool. Its not the end all be all but for a DIYer it gives me like 95% of what I need. Then I have an INPA virtual machine on my laptop with a USB to OBDII port cable that can fill in where this tool can't. Anyway just something to consider as a future investment.

A log like this can give you a ton of good information:

https://datazap.me/u/lookalikehuuh/i...2-3-4-12-17-18

I captured this with MHD and uploaded to datazap.me.... in the example here my LPFP was weak and losing pressure down to 50ish PSI under load. You can see though how my HPFP rails stay well above 2000PSI until I let off the accelerator at 6100 RPM.

[redz06]

The data I have cited are not all of the data that the OBDII reader recorded, just enough such that the trends and reactions are evident.

RPM Engine Load FRP
3133 22% 22 psi
3233 47 2078
3312 54 1933
3421 69 1722
3550 87 1395
3700 88 1408
3977 88 1358
4266 88 1222
4519 88 1105
4817 88 995
5510 67 1048
5530 24 75

What are the pretty curves on your datalogger more than just a graphical representation of these same datapoints? The importance is not the pretty picture, but the knowledge that can look at the data or the pretty curves and interpret whether the systems are working correctly, and if not, what is the cause? What is causing my engine load to flatline at 88 percent from 3500 to 5500 RPM, all while fuel rail pressure drops from 1400 to 1000 psi, and then at 5530 RPM to 75 psi, the output pressure of the LP pump?

I want to believe that the heart of the problem is a damaged quantity control valve, which is located at the top of the HPFP, unless this control valve is putting the HPFP on 100% recycle and allowing the low pressure inlet pressure to reach the fuel rail, I do not see how the fuel rail pressure can be as low as 75 psi. BTW, on cold starts where fault code(s) are set, the fuel rail sensor also says that pressure at the end of the fuel rail is 75 psi.

[swellengear]

My money is on a dead hpfp. The 75psi is the hpfp being put into bypass mode, so that you can limp home. The rail pressure sensor is seeing the lpfp's pressure.

[redz06]

Well, I definitely screwed up the title as my BMW is a 2011 model, not a 2008. It is definitely a N55 engine. Swellengear, I believe you are correct on the cause so I have ordered a new OEM (not rebuilt) HPFP and a set of intake manifold gaskets. So my money is on the hpfp as well.

[swellengear]

Fingers crossed! Let us know if it solves the issue.

[redz06]

Despite ISTA showing that the HPFP, the LPFP, and the regulator are OK, ISTA gives a warning that its recommendations do not reflect the performance under load. I purchased a new OEM HPFP and had it installed, and at the same time had the HP hose and the fuel rail ultrasonically cleaned. Since then the engine runs fine and there have been no fault codes lodged.

Getting to the HPFP requires removal of the intake manifold, so I asked that the shop have a look at the intake valve/port deposits. After all, the N55 has 100k miles on it. The intake valves/ports did not look that bad. The shop squirted a little solvent on them and called it a day.

[swellengear]

Glad to hear you got it sorted!