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Thread: Incorrect 4L80E Shift Points

  1. #1

    Default Incorrect 4L80E Shift Points

    Hello. Details of what I'm working with. Using a Holley Terminator LS MPFI system (Dominator ECU). Engine 6.0 liter LQ9. Transmission is a 1996 4L80E with a turbine sensor and VSS sensor. I've ensured the connectors are correctly installed on their proper sensors, VSS being the aft sensor.

    What's going on is the speed signal I see on the handheld while driving is low by about 20% across the range. Tire size is 37", gears are 4.86 and those parameters have been correctly inputted into the EFI software. I'd like to know why it's not accurate and what I could do to fix it.

    Also have a situation where around 25 MPH actual road speed it'll shift from 2nd to 3rd and if I don't apply more throttle and accelerate to 30 MPH, or above, the ECU will apply the clutches and release them, over and over till I either downshift manually or accelerate to a speed above 30 MPH. Odd behavior, not sure if related to the overall low speed signal.

    Main question is, how do I get the speed signal accurate that I see on the handheld? Just play around with tire size and gear ratio till it's correct? I figured it should just be correct since that's what is physically on the rig. I just feel like there's something I'm missing, so I'm asking for advice.
    Last edited by JeepCJ-6; 04-22-2019 at 11:36 AM. Reason: Spelling Error

  2. #2

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    The 20% low speed signal was incorrect, not what is going on. OK so more accurate information. When I sit in the driveway and apply a little throttle in park, neutral or any gear I see the MPH climb even though I'm not moving. There is no turbine shaft speed, just says zero all the time. At idle and parked, MPH saying 12 MPH. So I swapped turbine speed and VSS connectors on the trans (maybe they're labelled wrong) and now I'm reading 720 RPM at idle for turbine speed where before it was zero.

    Now when I drive it there is no MPH reading, just zero and it won't shift out of 1st gear, but turbine speed RPM climbs as expected. I guess next thing is to look inside hole where VSS goes and see if there's a tone ring. I remember doing that before I installed the trans, so I'm fairly confident there is a tone ring in there. Perhaps I have a bad VSS sensor. I'll check the wiring from the VSS to the ECU and if all good, I'll try swapping VSS out with a new one.

  3. #3

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    I popped the VSS out and looked inside. It looks just like this picture (not my transmission, click to make bigger). So this means I don't have a VSS reluctor ring correct? This really sucks. I'll have go to plan B, I guess. Oh and the turbine speed & VSS connectors were labelled wrong on my brand new harness. Confirmed by doing continuity checks.

    Click image for larger version. 

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  4. #4
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,384

    Default

    Did you have the transmission rebuilt or did you buy it used?

  5. #5

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    I bought it from a junkyard and then had it rebuilt. That makes this a lot worse because they were in there and it would have been easy to add the ring. I thought it had the ring when I looked. Clearly did not know what I was looking at till this morning.

  6. #6

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    Speaking of plan B for VSS, I'm not pulling the transmission and having it torn down to install a 40 tooth reluctor ring. I have to provide the 128K PPM signal another way. Now to figure out which way is best. There are a few options. Anyone ever use the Dakota Digital SEN-01-128 high frequency pulse generator? They claim it re-creates the 40 tooth reluctor signal and is compatible with a OEM GM LSx ECU, so it should work with a Dominator, since Dominator is looking for same exact signal. I got confirmation from them this morning it produces an A/C sine wave, not a square wave like a hall effect would produce. I'm gonna try it out and see how it works.

    If that device does not work out for me then I'll try to install a 40 tooth ring inside the tail-housing of the NP241. Currently it has a cable drive, hence the desire to run the Dakota Digital SEN-01-128. Should be able to swap tailhousings to get a reluctor ring and sensor to provide the VSS signal I need. Then I still have the problem of high/low range gearing and how that will effect shifting. Guess I'll have to reconfigure the gear ratio in the handheld to get proper shifting when in low range. Does that even sound feasible?
    Last edited by JeepCJ-6; 04-23-2019 at 12:08 PM.

  7. #7

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    Dakota Digital 128K PPM pulse generator saved my bacon. I’m back on the road and better than ever. Transmission shifts perfect and with a little adjustment of Gear Ratio & Tire Diameter, I’ve got the MPH reading on the handheld perfectly accurate, checked against GPS. So relieved and happy!

  8. #8
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,684

    Default

    That's a good update, thanks for sharing.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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