ACE1252

What would cause one bank of my long term fuel trims to jump wildly? Here is a sample of what my LTFT's are doing when the car is bucking @ around 1000rpm. Bank 1 for some reason is going crazy. Is this normal??? Keep in mind, this is only around 30 seconds from the first reading to the last. I find it odd that one is jumping around and the other is not.

B1 B2
3.9 10
3.9 10
3.9 10
14.8 10
14.1 10
6.3 10
3.9 10
3.9 10
3.9 10
3.9 10
5.5 10
8.6 10
7 10
8.6 10
8.6 10
8.6 10
8.6 10
8.6 10
4.7 10
8.6 10
3.9 10
3.9 10
3.9 10
3.9 10
4.7 10
3.9 10
3.9 10
8.6 10
3.9 10
7.8 10
8.6 10
4.7 10
8.6 10
8.6 10
3.9 10
8.6 10
8.6 10
8.6 10
8.6 10
8.6 10
8.6 10
14.8 10
14.8 10
14.8 10
14.8 10
14.8 10
14.8 10
14.8 10

Injuneer

Under what conditions did you get those readings? Was the RPM and throttle position changing, moving the PCM around in the various LTFT cells? How long had it been since the PCM was reset?

ACE1252

The PCM had been programmed shortly before(back to Bryan's CC503 timing table...increase in timing did nothing to curb bucking). The RPM was 900-1000. The throttle was 3.5-6%.

I may have stumbled onto something....the BLM boundaries....what exactly do they do? I know they have something to do with referencing a table, but I don't understand where the table is....

In the CC503 program, mine were set to 27, 40, 80. I changed them to 45, 60, 80. This was based on a Monodax post with a guy tuning a hotcam car. That seems to have helped the bucking. It is not neck snapping now. It is still there...but no where near as severe. I still need to do some more driving to see if it has made a big difference.

Before the boundary change, the fuel trim cell was 8/9. After the change it is now 4/5.

I will post up the complete log of the bucking before the boundary change and after.

Edit: Here is the log....both logs are on the exact same road and spot.

http://www.ace1252.com/Bucking_befor...ary_change.xls

Injuneer

Definitely something wrong with the Bank 2 BLM's. Highly unlikely that in the various cells you operated in, the right side BLM is exactly 10.0% (or 9.0% in the 2nd log). Almost seems like something has locked the the right side long term fuel trim. As a result of the LTFT being locked (???) on that side, the STFT's are having to do more of the work. They are averaging -10 to -11%, indicating that they are pulling out on average, as much fuel as the locked (???) LTFT's are adding.

You have to find out why that is happening before you go any further.

The cell boundaries are exactly that - boundaries. If you draw a 4x4 rectangular grid, and label one axis with the RPM values and the other axis with the MAP values, you will have a chart that shows you the boundaries of the LTFT Cells. There is no table, just the boundaries.

There is a crude representation about 1/2-way down in my scanner guide:

http://www.injuneer.com/ScanMast.html

bobdec

+1 I would go after why the right side LT BLM's are not updating.. not sure how that could happen usually an O2 not ready will block both sides from updating. I assume you are not throwing any codes as you did not mention it. Go after that first then secondly I noticed your timing is jumping around 7-10* when TPS, RPM and MAP are fairly constant around the 50-55 KPA/900-1000 RPM ranges you may have large jumps in your main timing table.

ACE1252

No codes to mention at all. The 900-1000 range @ light throttle is where the problem starts. Both pre-cat O2 sensors are new. The post-cat O2 sensors are old. My understanding is that post-cat O2's have no effect on engine performance(just checking cat condition).

I suspect the timing jumping around is a result of the bucking. I need to find out what is happening with the AFR when I crack the throttle. I'm not so sure the AFR shown by the Autotap log is correct. I need to know if it has too much fuel or too much air.

Would a wideband help me with this?? Which is better.....a LC-1 or LM-1?

I think the below videos are LC-1.....
http://video.google.com/videoplay?do...82557129&hl=en
http://video.google.com/videoplay?do...30570358&hl=en

Gauge seems to take a while to boot.....but I like it.

The above came from this post on monodax....I was looking for off idle issues....
http://www.monodax.com/forums/tunerc...le-issues.html

I'm going to try and find some old logs of the car to see if the trims are acting the same as above.

Other than the surging and bucking at 7-10mph, 900-1000 rpms@ light throttle....the car runs decent. Well....there is one other thing....it does run hotter in 6th cruising than in any other gear. I suspect that the mixture is leaning out a little to cause this....but I'm not sure. I will try to log that as well. Seems like I may have a really nice little problem.

Injuneer

Do you still have the front air dam in place? If not, that would explain the higher temps cruising in 6th gear.

Autotap can't measure A/F ratio. All is can read is the "target" A/F ratio the PCM is trying to set.

ACE1252

Yeah, I have the dam in place.

I guess I need to play with the fueling, in this KPA range, to see if it helps the situation.

ACE1252

Injuneer had this info on his site...but this picture kinda made it click for me....Is this matrix just a "quick" way of looking at what is happening with the fueling over entire engine operating range? In another words....instead of having a correction factor for each VE cell....they just summarize it into this matrix.

My understanding is that this is a window from EFILive. Some of this stuff from EFILive looks nice...



I'm still fighting my issue, but I will update when I have more information. Still logging and tweaking.

ACE1252

Oooo....it just hit me while tweaking this in the car now. This matrix is a way to provide flexible adjustment of the fueling across the rpm/kpa range. Instead of lumping the fuel adjustment into one value....they made this matrix which can provide more of a fine tune across a wider range. This is still kind of a summary...because the ultimate adjustment would be a correction factor for each VE cell.....correct?

Okay.....makes sense. Upon changing cams, I now idle at ~47KPA....used to idle at 30KPA. With this shift in air intake, without reprogramming the BLM's, I lose some of the BLM adjustment....interesting.

I'm going to try and adjust the BLM matrix to give my problem area it's "own" correction cell. I'm hoping that will help it learn what fuel it needs there....at the very least it will tell me what my O2 is seeing....for what it's worth.

My new values are going to be.....

BLM RPM - 1150, 1450, 2200
BLM MAP - 50, 65, 80

ACE1252

I've got another piece to the puzzle. I was doing some reading in the factory manual. It says that the post cat O2 sensor does play a limited role in the fuel trims. It is not specific on how, but in several spots it makes reference to that O2 sensor effecting fuel trims.

I'm having a problem on bank 2 with the trims. In doing some logging, I noticed what may be a problem with my O2 bank 2 sensor 2. It is not switching low at 2000 rpms like bank 1. Interesting. Look on the X axis at around time 1617.



Any comments? I need to do some more reading, but I'm not sure exactly what this means.

Interesting that it starts going low around 2300 rpms, then drop to 2000 rpms and it goes high. I don't know if this is a sensor issue or a cat issue.

bobdec

Would be interesting to compare O2 B2S1 with O2 B2S2, the down stream O2 (S2) should follow the S1 trend with a reading of lower CO2 (lower voltage) indicating the CAT is functioning. When the S2 voltages are not significantly improved (S1 starts getting close to S2) a CAT efficiency DTC s/b thrown. In you last picture I would like to see what B2S1 looked like at that same time frame. Are the wires all OK, an erratic heater circuit could slow down B2S2 switching..