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  • #1

    Help Reading Datalog...

    Ok guys, I got some good datalogs this past weekend. I have a few areas I want to try and understand. I'm attaching a snapshot of my log and I'll have to give you the values to understand.

    Black line is RPM
    Green line is Fuel Pressure
    Blue Line is Boost Pressure
    Purple line is AFR.

    The first thing that jumps out at me is the shift points and rpm drop. The 1-2 shift took place at 5850 and the rpm only dropped to 5140. The 2-3 shift took place at 5740 and the rpm dropped to 4180. Looking at the a spreadsheet I've got for gear ratios in the tranny, etc. I was suprised to only see a small drop in rpm on the 1-2 shift. This is an AOD.

    Secondly, you can see the fuel pressure taper off at the top even though boost was still coming up. I think this is my fuel system maxing out. Agree?

    You can also see evidence of the fuel system issues on the AFR line. It goes from about a 10.8 at the 2-3 shift all the way to about a 12.0-12.1 right before I shut it down. Most of 1st and 2nd was hovering around 11.5 or so.

    Thoughts?
    Tags: None
  • #2
    Bare with me... having trouble with the jpeg size.

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    • #3
      Doug, I'll reserve comment till the jpeg is uploaded - but, first.. is the RPM properly calibrated? I just don't see it bieng possible that it's dropping 1700RPM on the 2-3, although the 1-2 is realistic.

      I'd say you are right on the fuel system though - you're just drinking it dry at the top end (high demand, high load).

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      • #4

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        • #5
          The rpm is coming from the tach wire on the MSD box, so I don't see how it could be wrong.

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          • #6
            What kind of car is this? Does it have a stall converter? What kind of HP are you making? Your A/F line is really jagged. I would adjust the MAF transfer a little more. Perhaps it's blowing through the converter on the 1-2 shift?

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            • #7
              Turbo 302. 550rwhp/580tq. AOD with 2.4 first gear, 1.47 2nd gear and a 1.0 3rd gear. Rear end = 3.27.

              According to my spreadsheet, using the same shift points above,

              2.4 1st gear @ 5850 would be doing around 57mph with a 25.7" tall tire.
              1.47 2nd gear should be turning 3587rpm @ 57mph (at the 1-2 shift)
              1.47 2nd gear wound at to shift at 5740 would be doing 91mph.
              1.0 3rd gear should be turning 3896 @ 91mph (at the 2-3 shift)
              1.0 3rd gear should be turning 5480 @ 128mph (when it was shut down).

              I was expecting a drop into the high 3000's at the 1-2 shift and around 4000 rpm at the 2-3 shift.

              The car doesn't feel like it's slipping either on the converter or the clutches in the tranny but perhaps I'm wrong! The math doesn't add up. I suppose there will be some slip on the converter, but I didn't expect the data above.

              The a/f is sampled every .08 seconds. If I focus in on just the 3rd gear portion of the graph (like a dyno tune) the variance isn't nearly as jagged, however it does steadily rise as boost builds.
              Last edited by Doug Hatton; 11-15-2010, 02:35 PM.

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              • #8
                Yes, looking at AFR in your 1:1 gear offers the best readings. Sounds to me like you need a different converter.

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                • #9
                  Originally posted by Doug Hatton View Post
                  Turbo 302. 550rwhp/580tq. AOD with 2.4 first gear, 1.47 2nd gear and a 1.0 3rd gear. Rear end = 3.27.

                  According to my spreadsheet, using the same shift points above,

                  2.4 1st gear @ 5850 would be doing around 57mph with a 25.7" tall tire.
                  1.47 2nd gear should be turning 3587rpm @ 57mph (at the 1-2 shift)
                  1.47 2nd gear wound at to shift at 5740 would be doing 91mph.
                  1.0 3rd gear should be turning 3896 @ 91mph (at the 2-3 shift)
                  1.0 3rd gear should be turning 5480 @ 128mph (when it was shut down).

                  I was expecting a drop into the high 3000's at the 1-2 shift and around 4000 rpm at the 2-3 shift.

                  The car doesn't feel like it's slipping either on the converter or the clutches in the tranny but perhaps I'm wrong! The math doesn't add up. I suppose there will be some slip on the converter, but I didn't expect the data above.

                  The a/f is sampled every .08 seconds. If I focus in on just the 3rd gear portion of the graph (like a dyno tune) the variance isn't nearly as jagged, however it does steadily rise as boost builds.
                  The converter is not the problem, I'd say more along the lines of a premature shiftpoint is causing the engine to fall out of the power band and taking forever to recover. The higher rear gearing is problably not helping any either. The converter, is still a possibility, but most likely the LAST one I'd look at. MOST cars will never see more than a 1,000RPM drop on the shift.

                  The A/F we are seeing in the screenshot has no smoothing applied - so we are most likely seeing every sample. Also, a VERY slight misfire will create HUGE spikes in the A/F. Those misfires could be something as simple as a plug going away, a loose gap, a bad wire etc. (this is where the smoothing comes in handy)

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                  • #10
                    Is the fact that it's a lockup converter a factor?

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                    • #11
                      yeah, that has a lot to do with it too.

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