Have you replaced the O2 sensors yet? At the least the two pre-cat sensors. The replacement interval is 100k, you are 25k over.


So, lets get that done.


reference: https://www.bimmerfest.com/forums/sh....php?t=1158473



Next, something is up with bank 2. I assume you have looked up short and long term fuel trims- maybe read a few websites, look at videos. The short term FT will fluctuate and, over time, will then influence the long term trim.


When I look at both banks, you can see the STFT goes postivie and negatve (the print outs have a range of values at the top- you can see it was moving around). Likewise the LTFT has excursions both + and -.


However, the bank 2 seems to be trending towards + in a big way. Both its range and current value are signicantly more.


This means the DME is seeing a relatively lean gas mixture at the O2 sensors- and it is having to add fuel (hence the + value on the fuel trim) to get the mixture back to target.


What could be making the mixture lean? Too much air? Is there an air leak in the intake? A small hose w a crack, fitting loose?



Can you run a vanos function test w your software? Post those results.

Well, it was almost $2 in entertainment value. Amazing how one "expert" can go straight to the most expensive part to replace and dismiss any other possible causes, while the other essentially says ignore that part and just do a tuneup, don't worry, and be happy.

OK, I will go ahead and replace the upstream sensors. They are pricier than the downstreams, so I will do some eBay shopping.

Thanks for the link, looks like a good thread. Will view in detail after I get off work this evening. Yes, I have been reading and watching youtubes on fuel trims, trying to get my head wrapped around it all.

I did notice the high LTFT on Bank 2. So, maybe I need to go snooping around all my hoses and air intake, etc. Wonder also if that lean condition could be caused by a fuel system problem. I would have thought that would trigger some kind of fuel system code, but maybe not, I don't know if it has any way to sense that. Maybe a bottle of Techron would be worth a shot.

Not sure if OBD Fusion does the vanos test. I will check on it.

Thanks!

When you say 'fuel problem', are you thinking 'something wrong with the gasoline itself'?!? No, that is NOT the issue.

I suppose there could be some injector or fuel pump issue, but I tend to ficus FIRST on the most likely. A feul pump issue would impact both banks equally... Bad injectors? Much less likely that an air leak.

No, not suspecting the fuel. I've been through many tankfuls, multiple brands and a bottle or two of fuel treatment since this all started, with no real difference observed.

OK, just a little update. Ordered the upstream O2 (air/fuel ratio) sensors and received them earlier this week. Trying to get them in this weekend.

I have a nephew-in-law who works as a tech at a Toyota dealership. Regarding the vacuum leak theory, he is doubting it b/c he thinks if that were the case it would be affecting both banks, not just Bank 2. I see his point, but then I also feel like it would depend on a lot of factors, not the least of which would be the location of the leak -- if there is one.

Yeah, a good point- although it can depend on location a bit. Can also be a leak combined with old sensor on one bank...



Can you perform a VANOS function test? When vanos soleniods become fouled w old oil, sludge, they can become sluggish and lead to odd performance issues. Not bad enough to throw a code, but they will either fail or show borderline VANOS test results. Should be a program in ISTA or other BMW-specific code reader/computer to do this. A sluggish vanos on one side can mean that side is not seeing the right AFR for part of the RPM range- you get hosed AFRs but it is never so bad, all the time, to trip a full AFR error code



Also, it has been broadly reported that throttle response is poor when the vanos isnt properly adjusting between low and higher RPMs.

Not sure. I will have to read up on VANOS (variable nockenwellen steuerung -- see what I've learned already?). Not sure if OBD Fusion gives a reading for that.

My O2 sensor socket did not fit yesterday so I bought one last night. Hope to dig back into it sometime today. Concerned about how far around the back of the engine I am going to have to chase to find the other end of the O2 wiring harness for Bank 1 Sensor 1, and about how tough it's going to be to reach Bank 2 Sensor 1. Probably less than 50/50 chance these new upstream sensors will fix the problem, but as you say, they need to be changed out anyway.

Read a few articles & watched a few youtubes on the VANOS. Sounds like an interesting avenue to explore, and I would like to get some readings.

Sounds like the VANOS is especially sensitive to oil viscosity. I admit I am way behind on my oil change schedule, and I could see that possibly affecting it. Yes, I know, I know. But, I was in an awful accident last year, spent a week in the hospital, and literally almost died. Thank God I didn't, but I got behind on a lot of things and I'm still trying to catch up. I do run Castrol Titanium 5W30 full synthetic though, and normally change annually or at 20K. It's been way over a year but the wife really doesn't put that many miles on it, so I really haven't been that concerned about it.

Give me my reprimand about the oil, and no doubt I need to go ahead and refresh it and the filter, but I do have a little trouble imagining that the VANOS would affect only Bank 2.

I don't know much about the Castrol Titanium oil you're using. I know that after 10k miles, the oil I use is pretty spent due to detergent depletion and excessive thinning. Why not grab a sample of your used oil at your next oil change and get it analyzed?