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Thread: Gen 3 Weird Transmission Behavior

  1. #1
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    Gen 3 Weird Transmission Behavior

    Me again. One thing at a time. I have been driving my swap about 1.5-2 miles a day just to give it some practice (get it up to temp, load, break in, etc.)
    I have yet to make it road legal so I can only go as fast as my brakes will stop me in a parking lot (about 35).

    Long story short I have a B&M Megashifter, 2004 4L65E with a mild shift kit, heavy duty clutches/bands etc., 2,800 stall converter.

    When I shift it, the PRNDL status is spot on (P-R-N-D4-D3-D2-D1) BUT the Transmission Current Gear doesn't seem to jive with the PRNDL. It's good in first, but then you slap it to 2nd, and wait and wait and wait. No shift. Then you slap it into 3rd, still on the gas, and it shifts, into 'a' gear (maybe 2nd? feels like 2nd).

    It shifts fine all by itself (way too early for my liking but whatever), but I'm missing a gear somewhere, either I'm skipping from 1 to 3 and missing 2, or I'm starting in 2 going to 3 and missing 1. Either way, it doesn't seem to be commanding right.

    I will again recheck the shift cable, but in manual mode I can feel 4 distinct Drive positions, so I think its a command issue.

    Attached is my current tune and my most recent drive logs.

    P.S. On an unrelated note, after installing an exhaust (true dual, x pipe, magnaflow 4x9's) and still running in open loop, I am getting a lot of hesitation off idle to about 1,500 and then it smooths out.


    Thanks in advance for all who reply, I'm new to this. All help is appreciated.

    dd4.hpldd5.hpldd6.hpldd7.hplBase Tune 1.1.8 adjusted speedo, throttle follow.hpt

  2. #2
    Senior Tuner kingtal0n's Avatar
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    use scanner to manually apply gears and be sure of which ones are missing or not

  3. #3
    Tuning Addict blindsquirrel's Avatar
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    You need to be logging a channel called 'Trans Current Gear' (and a bunch of other trans-related stuff) to see what's happening. PRNDL status isn't anything other than what position the shifter is in; this is not going to behave like a manual valve body just because you manually shift it. It still shifts only when the speed/RPM requirements are met.

  4. #4
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    I did the manual gear command through the scanner. I'm missing 1st. Im starting in second. Trans current gear in the "1st" position on the B&M reads 2.

    Cable adjustment???

  5. #5
    Tuning Addict blindsquirrel's Avatar
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    If you start the engine, put the shifter in D4, 'trans current gear' should show '1st'. Does it show '2nd' when you do that? If so, that's not a shifter issue.

    This is an electronically-controlled fully automatic transmission. What it sounds like you're expecting with the shifter position vs current gear would only happen with a full manual valve body.

  6. #6
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    Quote Originally Posted by blindsquirrel View Post
    If you start the engine, put the shifter in D4, 'trans current gear' should show '1st'. Does it show '2nd' when you do that? If so, that's not a shifter issue.

    This is an electronically-controlled fully automatic transmission. What it sounds like you're expecting with the shifter position vs current gear would only happen with a full manual valve body.
    Ok so basically. If I leave it in D4, the current gear when stopped is 1. And I get 2,3,4 etc. It's fine by itself. And if I use the scanner to command each gear it's fine. I can go in 1st and hold 1st, go in second and hold 2nd, and so on. But when I use the ratchet action to go through the gears, it starts in 2. When it's supposed to be in 1, it's in 2.

    The only thing I can think of is maybe the lever isn't going back far enough?

  7. #7
    Senior Tuner cobaltssoverbooster's Avatar
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    what shifter do you have? some companies offer two different cable bracket assemblies for use with prndl switches to provide correct range.
    did you check this by removing the cable and manually shifting the prndl to 1st and see if it takes it?

    like b&m ratchets use 70499 with prndl switch installed and 35498 without prndl installed
    2000 Ford Mustang - Top Sportsman

  8. #8
    Tuning Addict blindsquirrel's Avatar
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    Disconnect the cable at the trans lever, put the shifter in D1, move the trans lever by hand to D1, see if they will still line up. You can (should!) do that for each shifter position. Sometimes the ratio is wrong with aftermarket shifters as they're pretty much meant to be universal*. To work out if it's correct you have to measure the amount of cable travel at the shifter going from P to D1, and the amount of travel at the trans lever going from P to D1, and alter the length on one of the pivot/arm lengths until both ends stay in sync through the entire travel.

    *'universal' means, in a lot of cases, that it won't fit anything

  9. #9
    Tuning Addict blindsquirrel's Avatar
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    Or... is this an issue where the shifter is in D1, trans is physically in D1, but the PRNDL is reporting something other than D1 to the PCM?

  10. #10
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    Quote Originally Posted by blindsquirrel View Post
    Or... is this an issue where the shifter is in D1, trans is physically in D1, but the PRNDL is reporting something other than D1 to the PCM?
    No. The lever is in D1 (verified twice), the PRNDL is saying D1, but the trans is actually is starting in second.

    If its in D4 (OD), it starts in first. If it's in D3 (drive/no OD) it starts in first.

    Basically, automatic 1st is there, but manual first is missing. I can't MANUALLY get it to be in 1st.

    Called the guy who built it, he's claiming it's a software issue and said it sounds like an MLPS/Range/Neutral safety/PRNDL whatever you wanna call it switch. But the PRNDL switch is correct. The transmission current gear is not.

  11. #11
    Tuning Addict blindsquirrel's Avatar
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    So if you are rolling at say 10mph, shifter in D4, current gear shows 1st, and you pull it down to D1, it shifts to 2nd?

  12. #12
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    Quote Originally Posted by blindsquirrel View Post
    So if you are rolling at say 10mph, shifter in D4, current gear shows 1st, and you pull it down to D1, it shifts to 2nd?
    That's correct. It goes 4,3,2,2. Manual first doesn't register.

  13. #13
    Tuning Addict blindsquirrel's Avatar
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    Doesn't register? You mean doesn't register in the log for the PRNDL, or for Trans Current Gear? Remember, there are four actual states we're discussing here, let's not mix them up. Shifter position (not shown in scanner), PRNDL Status indicated in scanner, Trans Current Gear indicated in scanner, and the real physical gear the trans is in (also not shown in scanner - just because the computer thinks it's in a particular gear doesn't mean it is). I just want to make sure we're not dealing with a mismatch between reality and what's indicated in the scanner, and confusing that with an actual gear change in the trans happening when it shouldn't.

    I want to see it shift from 1st to 2nd when the shifter goes from D2 to D1. Light or no throttle, 5-10mph. Does it go the other way as well, trans in 2nd gear with shifter in D1, move it to D2 it downshifts back to 1st? And the trans really truly shifts gear, you can feel it?

    If you're stopped, shifter in D1, you take off - it definitely pulls away like it's in 2nd gear? And not 1st gear but the scanner is incorrectly reporting Trans Current Gear = 2?

  14. #14
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    Quote Originally Posted by blindsquirrel View Post
    Doesn't register? You mean doesn't register in the log for the PRNDL, or for Trans Current Gear? Remember, there are four actual states we're discussing here, let's not mix them up. Shifter position (not shown in scanner), PRNDL Status indicated in scanner, Trans Current Gear indicated in scanner, and the real physical gear the trans is in (also not shown in scanner - just because the computer thinks it's in a particular gear doesn't mean it is). I just want to make sure we're not dealing with a mismatch between reality and what's indicated in the scanner, and confusing that with an actual gear change in the trans happening when it shouldn't.

    I want to see it shift from 1st to 2nd when the shifter goes from D2 to D1. Light or no throttle, 5-10mph. Does it go the other way as well, trans in 2nd gear with shifter in D1, move it to D2 it downshifts back to 1st? And the trans really truly shifts gear, you can feel it?

    If you're stopped, shifter in D1, you take off - it definitely pulls away like it's in 2nd gear? And not 1st gear but the scanner is incorrectly reporting Trans Current Gear = 2?
    The transmission is truly in second. It pulls away like it's in second. The rpms act like second. If I have it in D1, it's in second. If I shift to D2, nothing happens because it just stays in second, if I shift to D3 THEN it shifts because it's going to third. The trans current gear says second too. The trans current gear is accurate, because it also tells me I don't have a manual first gear.

  15. #15
    Senior Tuner kingtal0n's Avatar
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    when I pull the fuse for transmission harness it defaults to second gear and seems to stay there

  16. #16
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    Quote Originally Posted by kingtal0n View Post
    when I pull the fuse for transmission harness it defaults to second gear and seems to stay there
    What fuse would that be?

    And to reiterate:
    PRNDL Switch: P-R-N-D4-D3-D2-D1
    Shift Mode: Normal Shift- Normal D3- Normal D2 (Never changes mode to Normal D1)
    Transmission Current Gear: never goes into manual first/true low

  17. #17
    Senior Tuner kingtal0n's Avatar
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    If you go to the step by step re-working process for the harness
    https://www.facebook.com/media/set/?...5211824&type=3

    There is a step here
    https://scontent.fmia1-2.fna.fbcdn.n...a5&oe=5E1D91E5

    where power is applied to the transmission via it's harness component.

    In a swap, I put a fuse on that wire. It came loose once and I noticed the trans went right to 2nd gear and stayed there. Was very annoying momentarily

    make sure prndl is selected in the hptuners. When I finished my 4l80e swap I had a situation where it too didn't seem to display the correct gear in the scanner. But then I noticed somehow PRNDL got disabled (not sure how it happened, I thought it was always on)

  18. #18
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    Any update? I'm having the exact issue with my 4l80e . I shouldve checked it first, but I threw a new prndl switch and a new tfp sensor in it ,and it still takes off in 2nd when I select manual low, or d1 . Scanner says 2nd gear is commanded .

  19. #19
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    Quote Originally Posted by BGAuto1979 View Post
    Any update? I'm having the exact issue with my 4l80e . I shouldve checked it first, but I threw a new prndl switch and a new tfp sensor in it ,and it still takes off in 2nd when I select manual low, or d1 . Scanner says 2nd gear is commanded .
    Post the file.