1993 t56 with 1995 PCM -- Speedometer not working - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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Old 09-07-2011, 02:06 AM   #1
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Default 1993 t56 with 1995 PCM -- Speedometer not working

Hi guys,

I'm having problems with my t56/Camaro LT1 setup. I'm using a 1993 T56 with a 1995 Camaro LT1 tune. My speedometer in my conversion car just ins't working and I cant figure out why.

The car is a 1984 Jaguar XJ6 - initially I had a 4l60e behind the LT1 but I switched to a T56. Everything is working minus the Speedometer.

In the original Jaguar application, the speedometer is fed electronically, just like the LT1 -- I had purchased a converter box to change the signal that the 4l60e gave off to function with the Jaguar speedometer. The problem now is, with the t56 I'm getting no movement at the speedometer at all.

I'm not sure if this has to do with the tune that I have -- the 1995 camaro LT1 tunes worked with a different VSS sensor (different pulses per revolution) than my 1993 -- however I have read that the PCM outputs the same signal if using a 4l60e or a t56 (95) to the speedo regardless of pulses.

I'm just not sure where my problem lies -- the converter box worked just fine with the 4l60e, and now its not so the problem lies somewhere in the system.

Does anyone have any ideas what I should check?
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Old 09-07-2011, 06:16 AM   #2
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If you got the speedo working with the 4l60E and changed to a t-56, the most likely suspect, imo, would be the vss in the t-56. Thats pretty wild having a 6-speed in a jag xj.
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Old 09-07-2011, 10:20 AM   #3
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Think we discussed this on another forum, but I missed that the A4 to M6 conversion was done with a 1993 donor. First, using Freescan or Tunercat is your speed reading corrrectly at the PCM ? If not Here is some info on VSS stuff for Chevy transmissions. Note the some of the '93 LT1's used an AC sine wave from the VSS where all the the '94 and up used a DC Pulse from the VSS also the '93 3.55 first gear T56 used a different reluctor 11 pulses/rev than the standard 17 pulses/rev. Not sure which '93 you used so could be the '95 PCM may not be reading the VSS if it's an AC sine wave. If so you may need to move the Dakota box to the T56 VSS output and set it to convert the AC signal to a 17 pulse/rev DC pulse to the PCM.

1. The two-pulse (2000 pulses per mile) square wave (D.C current or direct current) used on all TBI
engines thru 1992, all computer-controlled-carbureted engines, and on 1985-1989 TPI engines.
2. A four-pulse (4000 pulses per mile) sine-wave (A.C. current or alternating current) signal is
required by the 1990-1993 TPI, 1992-1993 LT1 engines, and 1990-1993 Camaro 3.1/3.4 V6
engines.
3. A 40 pulse per driveshaft revolution speed sensor used on 1993 and newer trucks with automatic
transmission, 1994 and newer rear drive cars with the automatic transmission
4. A 17 tooth per driveshaft revolution speed sensor used on 1993-1997 LT1 engines with the Borg-
Warner 6-speed transmission. An 11 tooth reluctor ring is used on 1993 LT1 engines with the
Borg-Warner wide ratio (3.35 First gear) 6-speed transmission.
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Old 09-07-2011, 02:10 PM   #4
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Hey Bob,

Yep, we talked about this on MonoDax i think -- i didn't realize the VSS for the 93's T56 were different from the 94-97's (other than gear ratios).

I'm assuming that the 93's VSS is to blame. I'm not using a dakota box though -- it was custom made (although i think its similar in design... signal dampener)

I'm not sure how to tell apart the different T56's but I believe it is an earlier one (the car i pulled it out of was an early 93 Camaro)

Could i swap in a different VSS, like from a 95, or would that not work? I'm not sure how else i can get the box to work.
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Old 09-07-2011, 06:15 PM   #5
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After doing a little research, i'm not sure if I can just simply swap the VSS sensor, or if i have to swap the whole tailhousing -- ugh. Does anyone have any ideas?
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Old 09-08-2011, 03:07 PM   #6
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I would call Dakota Digital and see if the SGI-5 will work in your setup, they run about $80.00. I THINK you want to convert the 1993 VSS of 4000 pulses per mile AC signal to a 17 PP/revolution DC to feed the PCM. The PCM then converts 17 PP/rev to 4000 PP/mile signal to send to the the speedometer. But then you need another converter to convert the 4000 PP/mile from the PCM to the signal your speedometer accepts. This is getting way to complex, gotta be an easier way. Maybe posting post out here in the drivetrain forum would get a response to verify the actual VSS output.. Drivetrain - CamaroZ28.Com Message Board

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Last edited by bobdec; 09-08-2011 at 03:24 PM.
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Old 09-08-2011, 05:30 PM   #7
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I'm just trying to figure out if the newer VSS will even work in my trans -- if the older sensor had only 11 teeth, it stands to reason the reluctor rings would be different. Ideally I'd like to just be able to swap out the VSS modules and call it a day.

I verified my speedo converter is working by putting it in my friends Jag with a 4l60e -- speedo read fine. So it must be the sensor...
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