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Thread: MAF tuning issue with different gears

  1. #1
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    MAF tuning issue with different gears

    gents

    I've got a crate motor LS3 with Comp 54-469-11 cam, holley highrise intake and 102mm TB. I'm having some issues with the MAF tuning that I can't seem to figure out. I'm tuning in OL and using the AED WB.

    When tuning the MAF at highway speed, or when i'm in 4th gear, my EQ ratio is pretty good (-1.5 to +1.5 there abouts when averaged). The problem that I'm having is in the lower gears when I'm traveling 15-30mph. At these speeds my EQ ratio is somewhere between -8.0 to -11.0.

    I don't quite understand why it changes so drastically in a lower gear?

    The second issue that I'm having is also with the MAF, between 4350 and 4650 Hz (EQ ratio is -1.20 -1.06 and -1.09), while the airflow in g/s is 42.3 51.7 and 48.0. What would be causing such a spike in the airflow?

    If someone can have a look and help point me in the right direction, I would really appreciate it.

    ive attached the tune and log for your reference. MAF-1 Tune (using 104 MAF tune).hptMAF 1 log 3 OL Sept 08.hpl

  2. #2
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    I'm not in a spot to look at your files at the moment, but are you using any filtering in the scanner? It sounds like maybe an issue of non-steady-state data impacting your results.

  3. #3
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    Where is your maf sensor located? If it's really close to the throttle body, the low speed reading wont be a accurate.

  4. #4
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    Hi RobZL1, thanks for the reply. What filters would I be looking for? Presently the only real filters that I am using relates to the number of cell counts before the data gets logged, and no cell counts during idle.

    My apology but I don't know enough about this stuff to know what I am looking for. I had the scanning software set up by an experienced member of this forum and my knowledge of the process is a bit weak

  5. #5
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    Thanks for the reply. My maf sensor is about 12-14 inches from the throttlebody. That said, I have space issues at the front of the engine compartment. Immediately after the TB, I have 4 inch tube that completes a 90 degree bend, following which I have another 3-4 inches of straight tube and then my maf sensor.

  6. #6
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    Rob,

    This is the maf filter for the Lamda OL

    ([6310]<7 OR ([6310]>7 AND [6310]<15)) AND [50010.242]>176 AND ([50090.156]>20 AND ([50090.156.slope(200)]<5 AND [50090.156.slope(-200)]<5))

  7. #7
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    Quote Originally Posted by 32 Coupe View Post
    Rob,

    This is the maf filter for the Lamda OL

    ([6310]<7 OR ([6310]>7 AND [6310]<15)) AND [50010.242]>176 AND ([50090.156]>20 AND ([50090.156.slope(200)]<5 AND [50090.156.slope(-200)]<5))
    That should do the trick. On an LS3, the Fuel Trim Cell "<7" and "between 7 and 15" remove decel hits. FYI, FTC=6 and FTC=14 are idle-only cells. "<6" would be for normal driving, according to how the airflow mode boundaries are set in the tune. For what it's worth, I also ignore the "between 7 and 15" since that is when the EVAP is not active. You'll need to evaluate what makes sense for your application (e.g., you probably don't have EVAP if it's a ls-swap).

    I use something more like this for the throttle input:
    ... AND [50090.156.slope(3000)]<3

    It "tightens up" what actually gets considered to be "steady state" by looking at a total of 3 seconds of less that 3% throttle movement, as opposed to a total of 0.4 seconds of less than 5% throttle movement.

    All of that said:
    Did you factor in Injector Tip Temperature? When you are logging cruising at 35mph vs 60mph, is that during the same drive, or separate occasions? Did one set of data occur right after a reflash, by chance? If you are logging ITT, make sure it's not different between logging sessions, or during a logging session. There are a lot of pages on "rich after flash / injector tip temperature" that might be helpful to you here.

  8. #8
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    Thanks for the reply Rob.

    I don’t know about injector tip temperature. I will explore that in a few minutes and see if I can get an answer for you.

    As for the “flash” issue. This is the third log after a flash. I’ve had the issue of excessive fuel when tuning SD, so now I always complete 3 logs before I make changes. Based upon the last log, the rich EQ seems to always arise when driving at reduced speeds in the lower gears.

    I started the posted log with a drive in the highway, meaning I started recording while traveling 60mph. The excessive rich EQ arose after I began “start and stop” low speed driving. In the log it seems to appear quite regularly.

  9. #9
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    I just checked my log and I do not have any channel that logs ITT.

    Also, looking at the tune, it appears that everything with the injectors is stock, other than Flow Rate vs. Pressure (was increased by around 11%-12%) and Short Pulse Limit (1.500 ms vs 4.000ms). I forgot to mention that I'd gone to a 42lb injector and as such had to make a few changes to the tune.

    I'm in the process of researching the Injector Tip Temp right now. Thanks for the guidance.

  10. #10
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    Gents,

    I have completed another log using the same tune. Its my 4th drive since the flash, and as such I'm hoping that any richness associated with a recent upload should be gone. Further, I've also started tracking the Injector Tip Temperature as suggested above. The issue still persists and it doesn't seem to be connected to the injector tip temp. I will explain.

    Here is a summary of the drive, with some notes and comments.

    The log recorded my drive from work to home. The drive starts with 5 - 10 minutes of city driving, followed by 20 min of rush hour highway, followed by another 1 - 10 of street driving.

    As I analyze the results:
    1. at the start of the drive, when the injector tip temp is 90 degree, the I'm still 10% - 12% rich while traveling in the lower gears (1 through to 3).
    2. When I reach the highway, and the injector tip temp is 130-140 degree, I'm 1%-5% rich while traveling at highway speed (60 mph);
    3. When i return to street driving, in 2nd or 3rd gear and at a speed of around 24mph and an injector tip temp of 136, im still 10%-12% rich.

    I'm a bit lost with the results. Isn't richness supposed to increase as the injector tip gets hot?

    Once again, any thoughts and insights are greatly appreciated. I've been trying to do my homework and research the issue but I'm a bit stumped at the moment. Do you think its wise to simply try and balance the MAF tune as best I can, given the data, meaning try and get 5% rich in the lower gears and 1% - 2% lean on the highway?

    I'd attach the log but it was too big. I'm going to try and recreate the log when I drive to work tonight.

    Mark

  11. #11
    What gear did you tune the MAF at WOT in? If you tuned it for say, target lambda .85 at wot in fourth gear....it would be leaner in the lower gears. You want to tune it in the proper gear....usually 4th, so at lower gears, less load....it will be fine being slightly leaner.