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Thread: Snappy pedal with 5.3 Silverado

  1. #1
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    Snappy pedal with 5.3 Silverado

    I have here a 70's Silverado with 2003 5.3 stock engine. I notice it has LS2-type intake and headers. The T/B is 3-bolt model and the intake is 4-bolt and it has adapter in between.

    The problem is that the throttle response is very agressive. It's hard to drive moderately on slow speeds.

    I was thinking of changing "desired throttle area" but there is that notice that tampering with these values may brick the pcm. Should I worry about this?

    Tune and log attached.
    Attached Files Attached Files

  2. #2

    snappy throttle

    I am at work so i cant see tune .but i LS SWAP a 1965 c10 it was the same way . my conclusion the truck was light and easy to roll . I back the timing down at low rpms .2-3 degrees .IT calmed right on down
    learning

  3. #3
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    why is the IAC position stuck at 310 and not moving with the desired position?

  4. #4
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    Quote Originally Posted by lukearmstrong1990 View Post
    why is the IAC position stuck at 310 and not moving with the desired position?
    03 is ETC. No IAC.

  5. #5
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    Yes, this is drive-by-wire and the IAC was there because of the previous car I looked in.

    MAF is not functional right now and I was aiming to look for cells in spark table which are used when I start to move the car (this is when it's the most difficult with throttle response). I made a table with calculated airmass IAT/inj/AFR/MAP according to rpm but it shows 1.08-1.2 g/sec while moving without pushing the pedal so this is no help for me to see which cells in spark table I should decrease. I will get the MAF working and go from there.

    I would really like to make a new curve to throttle vs pedal position instead of playing with spark but I'm unsure how seriously I should take the warning in software.

  6. #6
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    I have now totally different spark table and it seems the problem has been cured. Or I have got used to it...

    I have been struggling with WOT shifts, the tranny seems to slip or have some annoying delay. The drivetrain isn't very old and the engine seems quite stock except for LS2 intake and headers. I removed T/B closing (helps to reduce torque while shifting) and now when it decreases torque in shifts it pops in exhaust due to late spark. It seems this tranny doesn't handle the torque without helps? I modified upshift pressures also but it didn't help on WOT.
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    Last edited by Tapi; 07-12-2019 at 02:25 PM.

  7. #7
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    Try logging delivered engine torque, I think you will find in the engine torque management I the pcm is pulling spark out to reduce the strain on the gearbox, I halved mine and found a big improvement, look at spark retard and torque loss
    Gen3 L59/4L60E LS3 cast manifolds, Small Cam change, 2800 Convertor, MPVI, using MTX-L for wideband tuning

  8. #8
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    I think the tranny has failed. I made at least 10 different tunes in which I raised line pressures and tested different ways to make the gear change quicker. Now it shifts 5 seconds late even with cruise speeds. I forced 2nd gear on with scanner and it doesn't pull at all. Other gears seem to work better. It seems when the gear is actually on, it handles the torque but the shift itself fail.

    I also put original tune in and the problem existed similar so it's not the changes I made.

    Perhaps shift solenoid problem?

    Tune and log attached.
    Attached Files Attached Files

  9. #9
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    I think if you are going to start messing with shift pressure, you need a gauge on the transmission.

    It could be doing something mechanical like starving for fluid (low fluid in the pan or clogged filter)
    Or any number of other things, and especially if there is a shift kit.

    I've noticed that sometimes more shift pressure doesn't always make harder/better shift.

    The torque management saves the transmission from being damaged. I suggest to keep using it. Let it pop with negative timing in the exhaust. You can turn it down some... but not too much

  10. #10
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    Quote Originally Posted by kingtal0n View Post
    I think if you are going to start messing with shift pressure, you need a gauge on the transmission.
    Please take a look at the log file I posted. It's like putting the lever to neutral when flooring it, there's just no resistance at all after the shift event.

    I raised shift pressures 10% but it had no affect so I backed to original values. The problem has got worse during these two days I've had the car. First I was worried about the shifting being so slow and the T/B closing same time. I was under the impression that the lag was caused by T/B but infact the log said the shift time error was something like 5 seconds...

    I haven't checked tranny fluid level though. I will do that.

  11. #11
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    I have a 4L60 that shifts perfect, scanner records Time of Latest 1-2 Shift as 0.3s, and Shift Time Error as ~6s, every time. I suspect the Shift Time Error numbers either don't mean anything, or work opposite what logic says. I changed my tune to get the Shift Time down from 1s to the current 0.3s and the error numbers went up, not down.

  12. #12
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    Quote Originally Posted by blindsquirrel View Post
    I have a 4L60 that shifts perfect, scanner records Time of Latest 1-2 Shift as 0.3s, and Shift Time Error as ~6s, every time. I suspect the Shift Time Error numbers either don't mean anything, or work opposite what logic says. I changed my tune to get the Shift Time down from 1s to the current 0.3s and the error numbers went up, not down.
    My 4l80e does that also. Doesn't seem change anything, but I've also disabled adaptive trans-pressure algorithms to keep it from trying to compensate.

  13. #13
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    I checked the fluid level and it was good. I called to a transmission shop which said that according to symptoms the freewheeling clutch has failed.