Welcome to CPGNation.com! Log in or Sign up to interact with the CPGNation community.

Tcu 4l80e now speedo shows half actual speed?

Discussion in 'TCI Support Forum' started by neo, Aug 12, 2013.

  1. neo

    neo New Member

    Joined:
    Aug 8, 2013
    Hi, i recently installed a TCI TCU (ez) in my 96 suburban 2500 with the 6.5 td engine mated to the 4l80e trans. I was able to plug the speed sensor for the tcu into a pigtail located on top the trans. It was taped to the harness initially. The speed signal must be right cause the speed indicator on the handheld is accurate. However, my dash speedo is now at half speed. I think this is causing my abs to fault as well. Any idea why the speedo is half? Everything else seems to be working. Any help is appreciated.
    Neo
     
  2. maxwell

    maxwell Moderator Staff Member

    Joined:
    Jul 5, 2012
    Hello
    The orange speedo output wire should be wired to the speedo. That particular year model requires a 4000 PPM signal to the speedometer.
     
  3. neo

    neo New Member

    Joined:
    Aug 8, 2013
    thanks, but a little more data

    So, there are two leads on the plug to the OEM harness, I resume one is for the signal, the other? what is it for? Reason I ask is that if I am going to send the signal from the TCI TCU back to the speedo, I will need to put the signal into one of the two leads in the original connector.
    Here is something else that I found:
    1. if I plug the TCI speedo input into this "pigtail" (a connector with a small bit of wire going into the harness) on top of the trans, I get proper speed on TCI, if I plug the OEM connector that was originally attached to the rearmost speed sensor on the trans, to the same pigtail connector on top the trans, the speed on the speedo is correct. If I plug either (TCI or OEM) into the sensor on the side of the trans (near the rear) I get half speed. However, that sensor is what I understand, the best place to get the speed for the tranny controller due to the fact it should reflect the tailshaft speed, which should be used to shift the trans, especially since this is a 4wd and if I use the sensor from the t-case (it shows correct on both the speedo and the TCI) the trans wont shift correctly when in 4wd.
    So, the best (in my simple mind) is to hook up the OEM input for the speedo into the sensor from the t-case to get correct speed on the dash (and not trigger the ABS alarm) and connect the TCI speed input into the rear-most sensor on the transmission, but SCALE it to 2X somehow. Is there a way (within reason) to scale the input speed through the settings? I tried "adjusting" the speedo, but it does not appear to be linear. It will reflect correctly at the speed in which I set it, but is not linear so that speeds above or below indicate correctly. For instance, I set the speed (was showing 7mph) when I was traveling at 15 mph by using the "set speedo" advanced function, but when I slow down, it goes to zero very quickly and when doing 30 is read like 42.
    If I can scale the input, then it would work well.
    As I understand this would fix the 4WD issue as well, where the tranny won't shift proper in 4WD due to the fact the speed is from the tailshaft and does not compensate for the 4WD.
    Help is greatly appreciated.
     
  4. maxwell

    maxwell Moderator Staff Member

    Joined:
    Jul 5, 2012
    For a 4wd application, you can either splice the TCU TOSS wires into the vehicle speed sensor wires or as you suggested, use the T-case sensor for the OE ECM and just scale the TCU speedo accordingly. The easiest way to accomplish this is the half the gear ratio when you go through the Setup Wizard.
     
  5. neo

    neo New Member

    Joined:
    Aug 8, 2013
    possible sensor?

    THanks for the info. So I am going to try changing the sensor and see if that helps, I figure I should eliminate it from being a culprit. The thing I am so confused about is that the speed coming off the rear most sensor SHOULD be identical to the speed on the T-Case unless 4WD-Lo range is engaged, should it not? These two reluctors (t-case and the rear of trans) should be identical, shoudl they not? I believe this becuase the rear most sensor WAS where the OEM speedo input plug was plugged. Now, when I plug it there, I get half speed. In order to get true speed, I have to plug into the pigtail. THis is really weird!
    Should the T-Case not be 1:1 unless 4Lo is used?
    Was there every any reason to have a half scaled speed output on the rear-most 4L80E sensor? Why would it have changed from just when I installed hte TCI TCU?
    You mention scaling it, the current R/P is 3.73 IIRC, the lowest I can go ont he R/P on the TCI TCU is 2.00, I would need half the 3.73 would I not?
    Why if I try and scale on the "Adjust Speedo" advanced tab, does it not respond linearly? COuld this be further indication of the sensor being bad?
    THis is the last issue to resolve, and it really seems to make sense to use this signal since using the tcase signal (although accurate in 2WD and 4Hi will not indicate correctly in 4Lo. THanks for your help.
     
  6. neo

    neo New Member

    Joined:
    Aug 8, 2013
    still confused

    I am still not there. I tried everything i can think of to dial int he TCI TCU using the rear sensor on the 4wd fitted 4L80E and still get a strangly scaled speed output. I am driving the dash speedo off the tailshaft of the t-case and it is rock solid. This is not where this input was originally hooked up though, now, it is the only one to work. It (the original) was hooked to the rear trans output. As I mentioned above, when I do that, I get, what apears to be, half speed. THis is driving me nuts!
    So, somebody, please tell me this: is the rear sensor and reluctor on the 4L80E not the same speed as the input into the T-Case? And, if that is the case, unless the t-case is locked in 4Lo, would that not be the same as the output ont he t-case tailshaft? THe t-case does not offer any increase in speed, it only reduces, so the two shafts, if I understand correctly, in front of the t-case and behind the tcase should indicate the same, right?
    THe sensor is definetley not the issue. I have swapped the front and rear and get the exact same results. any guidance or understandign is greatly appreciated.
    Neo
     
  7. neo

    neo New Member

    Joined:
    Aug 8, 2013
    A little more testing

    So i did a little more testing. I tried to fool the tcu by setting the r/p low (2.25) -the minimum is 2.00 and the tire size really large at 40" which is the max and still no luck. It will show low speed (below actual) at slow speeds. At about 20 it is accurate, then it goes over actual speed. At 40 it shows like 60! Its like it is not linear.
    Is there some way i can simply use the tailshaft sensor and not the toss as specified in the instructions and then trigger lower velocity shift points if the performace wire is grounded, make it run a 4-lo program instead of whAt it curreny would do? I understand the old one you could program on the pc and this would have been possible. Can i hook up a laptop and
    Make my own 4-lo program? Thanks
    Neo
     
  8. neo

    neo New Member

    Joined:
    Aug 8, 2013
    Both sensors have different waveforms

    THis weekend, I drove to the local pick-n-pull and cut a couple connectors for the TOSS/TISS off a wireing harness. I was able to make two patch cords, one from the TOSS and one from the T-Case VSS sensor. I used my Fluke handheld scope to look at the waveforms produced by both sensors. What I found was the T-Case VSS is way noisier, considerably higher voltages (12-15V at about 20 mph) and the period is scaled half the period of the TOSS. The TOSS signal is actually very clean and max amplitude is around 10-15 mV at the same speed. I have some screen shots of the signals at various (unknown accuracy) speeds. SInce i had the TCU connector disabled, it was unable to shift out of 1st, so my speed was limited. I could easilly see the two waveform periods get shorter, and the voltages (amplitude) increase as I sped the truck up.
    SO, why would the TOSS produce a clean, nice waveform, be the sensor specified in all the literature as the one to use (this was a huge factor in my decision to purchase since I knew I had to use this as the input in order to have accurate shifts in 4Lo) but I can't scale to this signal?
    I will pull the sensor tomorrow evening and look inside to insure the reluctor is centered properly. I suspect it is due to the super clean signal that it produced. By the way, I switched cables to insure my cables were not intriducing error and this was confirmed by the resulting waveforms on the scope screen.
    I really need some guidance on this one. THanks in advance.
    Neo
     
  9. maxwell

    maxwell Moderator Staff Member

    Joined:
    Jul 5, 2012
    Hi Neo,
    I believe you are speaking with Kevin here. He should be able to get you fixed up.

    Thanks
     
  10. kevin87turbot

    kevin87turbot Member

    Joined:
    Jul 27, 2012
    Location:
    Ripley, MS
    Hi Neo,

    I sent you two emails yesterday, but they both bounced back. Will you email me a pic of the output speed sensor hole at kwinstead@compcams.com ?
    Thanks!
    Kevin
     
  11. mihail

    mihail New Member

    Joined:
    Feb 9, 2014
    Hello I have the exact same problem. what solution was found???
     
  12. maxwell

    maxwell Moderator Staff Member

    Joined:
    Jul 5, 2012
    Hello,
    The 4x4 transmissions are different. Most do not have a speed sensor reluctor. Neo's was somehow triggering off of the planetary parking pawls, which was giving an incorrect reading.
     

Share This Page