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Old 01-31-2017, 02:57 PM
Join Date: Sep 2005
Location: New England
Posts: 131
btrvalik is on a distinguished road
just to clarify.. here is the pre and post O2 sensors for bank 2

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Old 02-03-2017, 09:01 AM
Join Date: Sep 2005
Location: New England
Posts: 131
btrvalik is on a distinguished road
I may have fallen into the trap of over analyzing. The original recommendation from my indy was to replace the MAF. When I went to order it, BravAuto suggested that I replace CCV and other maintenance items first - correlates with advise here and else where. While I still need and will replace the CCV, it seems to be working properly - and it's cold where I live. Yesterday, I finally gave in and threw a new MAF on - and now my fuel trims have fallen by nearly half after about 10 miles - I'm hoping they will continue to fall as I drive more.

One puzzeling aspect is that my CEL light when off after I tested my MAF with the propane test - and stayed off for the next couple of days / 4-5 trips. The fuel trims however, never came down - LT trims were sitting between 8-9.5 with ST trims bouncing all over. My post cat O2 also bounced around a lot

I must thank Kevin Kay for indirectly getting me to replace my MAF - we have been chasing and went he mentioned in a PM that he's changed everything except the MAF, I figured it was worth a try. Check our these plots.. not ready to call this solved since so many CEL solutions seem to be short lived, but I will report back in a few days if trims keep coming down and no more code - fingers crossed.

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Old 02-03-2017, 12:25 PM
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Location: Cook County
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upallnight is on a distinguished road
For my X, the long term fuel trims in bank 1 and bank 2 hover around +5, whereas the short term fuel trims hover around 0. See the my video.

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Old 10-18-2020, 12:09 PM
Join Date: Aug 2009
Location: Pennsylvania
Posts: 85
mendes9 is on a distinguished road
On your RPM / MAF what is the MAF reading is that Kh/h?
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Old 10-18-2020, 01:38 PM
Join Date: Oct 2013
Location: on earth
Posts: 1,081
puddinboo is on a distinguished road
Dont wait too long to replace the ccv , you dont want to hydro lock your engine by a frozen ccv and all your engine oil gets sucked up onto the top of the pistons. Bending connecting rods.
Originally Posted by btrvalik View Post
I do need to replace my CCV due to age, but I'm not sure this is my problem - plus it's really cold to take on and extensive job. Here are a couple more test I tried:

The system was already smoke tested and found no leaks, as a test for vacuum leak
  • Measure baseline vacuum (-13 PSI),
    Increase rpm to 2500 (momentary increase to -2)
    Back to baseline (-13 PSI) within ~20-30 sec
I then did a test to see what happens of I force it rich and then lean:
  • Warm up the car with a drive
    Make it go rich at idle by turning on an unlit propane touch in front of the MAF
    Let it stabilize back to baseline
    Create a vacuum leak by removing oil cap
From the resulting plots, the system seems to respond properly[LIST]
ST fuel trims go to ~ -28 when propane is on
ST fuel trims return to the baseline when propane off
Open the oil filler
ST fuel trims go to ~ +20
Close cap
ST fuel trims go to back to baseline

The fuel trims and from side to side do roughly the same thing
Trying to decide if it's time to take the indy BMW shops advise and replace the MAF - hate throwing parts at the problem since the MAF seems to track RPM fairly well but not sure what else to try beyond doing the whole CCV, DISTA, ICV, etc

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