P code expert?? What's the trim "system"?

[upallnight]

If you add the numbers for the Short term fuel trim with the number for the long term fuel trim it should total close to 0 (zero).

So if the LTFT is 10, the STFT should be close to -10 so when you add them together it should be close to 0 (zero).

The LTFT on our X does not change as quickly as other cars, but it should change.

[upallnight]

Originally Posted by btrvalik

As a bit of an experiment, I decided to scan / log my wife's CX-9 to get a better understanding of how a car that doesn't have a code reacts - perhaps a bit apples and oranges, but the basics of fuel and emissions controls seems to be fairly generic - oxygen sensors magnitudes seem to differ a bit between manufacture. Most of the reading see fairly similar to my X5 - for example if I plot MAF / RPM, the plots have the same pattern. The one that jumps out is long-term fuel trim. On my X5 the LT fuel trim will only change once every 10+ min. On the CX-9, it's changing every 20 sec or so.

According to a reference I found on the web:

The PCM’s definition of “short-term” is milliseconds, it acts incrementally, adding or subtracting fuel in small increments in an effort to hit the stoichiometric target.

the PCM is watching what’s happening in response to the changes in STFT. If STFT adds, for example, 3 percent fuel to the baseline and this makes the oxygen sensors happy, the PCM concludes that it ought to adjust the baseline. So it changes the “long term fuel trim” (LTFT). “Long term” is between 30 seconds and a minute. This creates a new baseline.

Based on the above, it would seem my LTFT is changing too slowly - up without knowing what is "normal" it's hard to tell.

@Kevin, Have you tried logging your LTFT? I'm using the Torque App and a BT OBDII which seems to work well.

Next time you get a SES light check the freeze frame data. It will tell you what the engine was doing when it threw up the SES light.

[kevinkay]

btrvalik, assuming you have the same 3.0i I have .......

another member axgordon - (and the credit for this to him) said his trim errors were do to leaks in these 2 caps on the intake.
I just pulled one of mine off, (the other was kinda stuck and I wont pull that one off until I get the replacements). The cap I did pull was loose and all cracked - photo below. I taped it up temporarily and cleared my code I will see tomorrow if it comes back. I will be extremely happy if this was my culprit.

The 2 lower photos were from axgordon

and Yes I have tracked trims with iPhone app OBD fusion I think I even did a "freeze frame"- but I dont know what any of it means.......

[kevinkay]

#15
#17

RealOEM.com - Online BMW Parts Catalog

[btrvalik]

Just checked those plugs and mine seem fine. Since it's warm this afternoon, I decided to poke and prod at some of the vacuum lines with a stethoscope to see if I could hear a leak. Didn't find anything so I hopped back in the car to pull it back in and low and behold, the CEL was off!. Now the question is what the hell did it. The only thing that seemed to effect the engine was when I pulled the CCV hose off the valve cover. I didn't notice much of a RPM drop when I pulled it off, but the idle jumped a bit when I put it back on. Wonder of I had a bit of blockage in that line that opened up? I also gave the post car 02 sensor wiring a "shake" but the signals still look the same. My fuel trims also look about the same.

[btrvalik]

here is a good reference on fuel trims.. https://www.cartechbooks.com/techtips/fueltrim

[Ricky Bobby]

Yep I did those 2 vac caps this spring, along with the 2 pieces of vac hose next to the ports with that white thing in the middle - and the entire SAP line from the passenger side of the manifold that ends on the "3rd port" that no arrow is pointing to, in your pic - the entire line is avail from BMW for $19 or so and has the 2 proper vac hose sections and a new hard line which is in the middle

[upallnight]

Hey Kevin,

I found a Great Video on how to determine where your fuel pressure is leaking out. I think that is the reason for all your current problem.

Eric O of South Main Auto in upper state New York is a great mechanic and produces some of the best DIY videos for do it yourselvers.

Here's the link to his video. If you want to be a better diyer or mechanic, subscribe to his channel.

https://www.youtube.com/watch?v=DL8toqPcXKA

[kevinkay]

Thank you!
Can you verify I connected the fuel filter (which is also the regulator) properly?

I pulled the back seat off and verified the BLACK line went to the electric pump (passenger side) and the BLUE line went to the syphon pump (drivers side)

I then connected the BLACK line (electric pump) to the "IN" on the filter
and the BLUE line (syphon pump side) to the "rtn" on the filter
Both of these photos I found on line also have the BLUE line in the center - "rtn"

I replaced my CCV - the code came back AND after some short rides I gained a rough idle - guessing my idle control valve not seated properly?

[80stech]

Kevin, If you have proper rail pressure and the regulator changes the pressure with engine vacuum(or better yet vacuum pump) then you have the lines on correctly.