2005 M6 with fast 102, cam, long tubes and exhaust. Car was recently tuned and ran great for a couple days. Drove about 3 hours and when I got home I noticed the car idling pretty lean on my wideband (1.3 lambda). Pulled out the laptop and logged it. Noticed the car was pulling upwards of 20% fueling at idle. I disabled closed loop with special functions and the car idled perfectly normal and drove fine, but whenever i reenabled closed loop fueling it would pull a bunch of fuel. just installed new o2 sensors and now the problem seems worst, its pulling out 25 percent even when im cruising now. Whats odd to me is that while this is happening, the narrowbands are reading nearly stoich (450mv) even though it is incredibly lean (yes the wideband sensor is accurate, it barely even runs when it starts pulling all that fuel). What could cause the computer to pull so much fuel even though its running insanely lean? Already checked for exhaust and vaccum leaks and found none, plus i would think that would cause the opposite issue. injectors were just cleaned and my fuel preasure was right at 58 through the entire attached log kind of stumped on this one, im attaching a log I took where it was the worst so far.

 

This looks like the o2 sensors are bad, maybe the harness going to them is melted or something. .450 across the board is what they will read unplugged.

Prehaps check your o2 extensions if you have them. Check the o2 sensor heater fuse too although I doubt that will be it.


The amount of fuel being pulled by the fuel trims do not match how lean it is by the wideband. Have you reached out to your tuner about this?

 

yes.. contact your tuner. I actually had the opposite experience. when I got my car, it was basically stock but a k&n. it would always drift the ltft lean and make it run blah at apart throttle. I went thru all the normal, all new o2 sensors, plugs. wires and stuff. Eventually I got a good deal on a hptuners and went ahead and went thru the tuning even thou it was stock. no dyno time for hp, just went thru the motions and made some changes.

all the lean chasing ltft stopped and the car runs much happier part throttle thru the gears. no clue why really but something wasn't happy.

 

I texted my tuner, he is out of state at the moment but next week when he gets back were going to look and see. There brand new sensors and while I was changing them I checked the harness and all looked good, one connector end was slightly melted but not enough to cause any issues getting it connected. I also checked he fuse and it was fine. It's raining now but when it stops im going to take another look and see. if i cant find anything ill just flash a tune i did that disables the fuel trims and just drive it in open loop until next week.

 

MAF sensor clean?

 

Yes, it was just descreened and cleaned thoroughly before it got tuned.

 

So i may have figured it out, only time will tell, ill keep this thread updated if it doesn't end up being fixed. Im 50/50 at this point just because alot would have to happen in a very specific order for me to have fixed the issue. The 3 hour drive back where the car started acting up was because i picked up a set of morimoto headlights. After installing them is where things got worse. The headlights use fuse #6 for DRL function, which is the O2 heater fuse, my thought is that having the headlights tapped into that fuse may have been throwing off there heating which greatly effected the o2 performance. I have just pulled that tap and reinstalled the original fuse and it made the latest drive (log linked) just fine, no hiccups. (The instructions and seller told me to tap #6) The reasons im not certain that was the issue are: the issue started the long drive before i installed the headlights, after lots of searching no one with these headlights has had a similar problem. SO, for this to have worked, my original o2's wouldve had to have gone bad on the drive back from getting the headlights, and the headlights themselves would have to be causing issues with the 02 sensors after i replaced them, which hasnt been reported from what i could find. Im not hopeful but only time will tell. Latest log linked.

 

The o2's are working now. Looks ok. I definitely think it was related to you tapping into the O2 heater.

You could stand to have some fuel pulled out of the MAF table. averaging around -12%

 

Yes that's what I'll be doing today, I was waiting for a new cold air intake to show up, my last one was pretty restrictive up top. So I'll be returning the maf once I install it.

 

Cars been running good since pulling the tap off of the O2 heater fuse. For anyone with the morimoto headlights having a similar issue, that's the fix