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Thread: need transmission tuning help....jacked up tune

  1. #1
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    need transmission tuning help....jacked up tune

    I've been working with this truck off and on for a while now and it has me all but stumped. It was partially tuned by another shop and is kinda jacked up. The owner just wants it to shift right mainly. I kinda started working on idle tuning too as its rough running and fueling was off a bit too....but that stuff is easy to fix.

    It has (supposedly) a FLT level 4 4L80E. I finally figured out my first problem last night was the VSS in the tranny was bad. I fixed that and resumed work this evening. Then i saw the tire size was way off and fixed that. Now it still doesn't shift right AND the speedometer is wrong as well as the vehicle speed in my scanner, when compared to my GPS on my phone. If i remember, the GPS showed 60mph when the scanner was showing close to 80mph and the truck's speedometer was reading under 50mph. 90% of the stuff i get to tune is either a manual trans or a stock auto, so i'm kind of out of my element here. I found a tune in the repository for the same year truck (2000) with a 4L80 segment swap. I tried loading all the stock shift parameters to sort of start from scratch and it still isn't anywhere near right. It wont shift at the commanded speed and when it finally DOES shift, it seems to only do it as i'm backing off the throttle. WOT shifting is way off too, but i think i can handle that once i figure out what is causing me this grief under normal driving conditions. The tune attached is the current one, and the log was the last one i made, not really the best but it demonstrates the issue a bit...if i could log my GPS and show a video of the speedo in real time it would help a lot too. The tune labeled "stock" is the one that was in the truck when i got it.

    Known mods are a Whipple supercharger, 42# green tops, & a built 4L80....the truck is supposed to also be .030" over with forged pistons, rods, 4.10 gears, worked over heads, and a small blower cam. nobody knows for sure what is done to it.

    If anyone knows what can be causing this, i'd greatly appreciate the help. I think it may have something to do with the VSS pulses or trans revs/mile but i just don't know when/why to modify those or what the outcome could be. It may even be a mechanical issue but everyone swears its good to go. it shifts very firm and quick when it DOES shift.
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  2. #2
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    Any suggestions? I'm not having any luck with this thing. Is it possible that the segment swap wasn't done properly?

  3. #3
    Senior Tuner Russ K's Avatar
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    What size are the rear tires?

    Russ Kemp

  4. #4
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    I'm not at my shop right now, but i believe they're 265/65/16. I'll double check later.

  5. #5
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    Could it possibly have wrong reluctor ring in it? Would that make it act the way it is?

  6. #6
    Senior Tuner Russ K's Avatar
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    Still need to know the tire size. Probably 265/65/18?

    Russ Kemp

  7. #7
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    I still haven't been out to the shop, lol, but I'm 95% certain they were 16's like i posted earlier

  8. #8
    Senior Tuner Russ K's Avatar
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    There are no tires that size, and need to know the gear ratio. Your making it hard to help you.

    Russ Kemp

  9. #9
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    Ok, I'll look as soon as i get home, sorry man. The gears are supposed to be 4.10's but i don't know for certain.

  10. #10
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    235/65R16...my bad

  11. #11
    Senior Tuner Russ K's Avatar
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    I set up your speedo, note that the tire dia is always shorter then the advertised dia to allow for the loaded radius. And your calculated tire dia didn't match the current tire dia.

    Also your trans will have max line pressure due to the SD tune, so I disabled the Max Line Pressure DTC's. So you may want to firm up the shift pressures if desired.

    And your truck has a vacuum referenced fuel pressure regulator, so your IFR & offset tables will need to be flat lined.

    Russ Kemp
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  12. #12
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    Wow, thanks, Russ. I'll give that a shot and report back. Thank you.

  13. #13
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    Ok, i know this sucks, but i don't have a log. My scanner wouldn't connect for some reason and i was in a hurry to get back to the house and deal with a minor emergency. BUT, the truck is still screwy. It seemed better on the 1-2 upshift at first but when i accelerated more it was clear it still wasn't right. My GPS was showing 50mph and the speedometer was reading 28-29mph....It takes forever to 2-3 shift and it doesn't happen until fairly high rpm/speed. I'm not sure it even went into 4th at all going down the highway.

    I dunno if this info is helpful...i know a log is ideal so i'll try to get one tomorrow and post it up, i just couldn't pull it off tonight for some reason.