Never ending System too Lean Bank 2

[Hangry]

I've had my 2004 3.0i BMW Z4 for almost a year and have not known it without a service engine soon light, most notably a P0174 error code.

The car had a rough idle that was fixed a week ago. A lot of work was done on the car by my mechanic, from replacing the fuel pump and fuel tank, to replacing air intake tubing, and most recently, a burnt O2 sensor was replaced. But no matter what, the service engine soon light came back on after a 10-20 miles after every fix.

Most recently, we found a burnt O2 sensor and replaced it and that finally got rid of the super rough idle. However the service engine light keeps coming on randomly every 20-30 miles after each time I reset it to see if it will come back. When I get the light, the car doesn't feel like it’s knocking or misfiring and it drives perfectly normal. Usually, the codes are only P0174 - System too lean bank 2, however twice now it has given me P0300 (Random/Multiple Cylinder Misfire detected), P0303 (Misfire Cylinder 3 Detected) and P0305 (Misfire Cylynder 5 Detected) as well (out of the 6 times that I have gotten a light). What should I look at next?

The car currently drives extremely well, the best I've ever had it. It is smooth, does not ever feel like it is misfiring even with the occasional codes. One thing I noticed, I am not sure if it is related, is that when I enter the OBD2 scanner, the ISO15765-4 CAN(11bit) and ISO15765-4 CAN(29bit) fails. Not sure if it is related can someone please clarify what that means. My mechanic thinks the system too lean errors might come from a faulty computer system. Someone has similar issues? If there was a vacuum leak or misfires, wouldn't they happen much more often so I wouldn't have the codes appear once every 20-40 miles?

 

[raymond.harper]

What scanner are you using, a generic or a model-specific one? https://z4-forum.com/forum/viewtopic.php?t=89212

 

[Hangry]

I’m using a specific bmw scanner Ancel BM700.

 

[Mike6]

I am no expert as still trying to trace a code on my car. But one question I would ask is how old is the battery. When they start to fail you can get all sorts of dashboard lights but car will still start and run well.
If it's more than 5 years old or you don't know it's history I would change it.

 

[raymond.harper]

You can get a cheap smoke detector test from eBay for around £60 but hopefully your mechanic will have done this test. Go into the OBD11 function and read the data stream to see what the fuel trims are reading. Also found this. https://www.e46fanatics.com/threads/e85-high-lean-fuel-trims-rough-running-obd-fusion-logs-z4-w-m54b30.1325778/

 

[Hangry]

I am no expert as still trying to trace a code on my car. But one question I would ask is how old is the battery. When they start to fail you can get all sorts of dashboard lights but car will still start and run well.
If it's more than 5 years old or you don't know it's history I would change it.

It is a brand new battery. Just had it replaced with the O2 sensor

 

[NZ00Z3]

If you want to do some data logs, the phone app is OBD Fusion. Read the below link to set it up. It gives lots of very good data to help with the diagnosis. Post the logs in DataZap.me and post links to datazap in here. I'll then have a look at the logs. You can see the sort of analysis that I do in the E46Fanatics thread that @raymond harper posted.

https://www.e46fanatics.com/threads/obd-fusion.1240733/#post-18380161

 

[Joez4]

If you want to do some data logs, the phone app is OBD Fusion. Read the below link to set it up. It gives lots of very good data to help with the diagnosis. Post the logs in DataZap.me and post links to datazap in here. I'll then have a look at the logs. You can see the sort of analysis that I do in the E46Fanatics thread that @raymond harper posted.

https://www.e46fanatics.com/threads/obd-fusion.1240733/#post-18380161

I have read many of your threads over on e46 fanatics mainly regarding negative long term fuel trims as my car's fuel trims are negative for both banks and I still can't work out why so I can most definitely say you certainly know your stuff and the op is definitely in the right place.

Without hijacking the thread anymore tho, do you think the atmospheric pressure reading in the dme plays any part on fueling, as on my car it always reads lower than it actually is compared to weather app for my area,

 

[NZ00Z3]

Without hijacking the thread anymore tho, do you think the atmospheric pressure reading in the dme plays any part on fueling, as on my car it always reads lower than it actually is compared to weather app for my area,

In short, yes. Happy to move this conversation to a PM or another thread, so as not to hijack the OP's thread.

 

[Joez4]

Without hijacking the thread anymore tho, do you think the atmospheric pressure reading in the dme plays any part on fueling, as on my car it always reads lower than it actually is compared to weather app for my area,

In short, yes. Happy to move this conversation to a PM or another thread, so as not to hijack the OP's thread.

Have created a new thread https://z4-forum.com/forum/viewtopic.php?t=150620