95 TBI into older 4x4 vss question

[dale]

My diagrams call is a VSSB, so that's what I'm calling it

I know the speed reading effects a lot. I've played with some OBD2 tuning. But I just want it to get a reasonable reading. But Ive also thought this evening. Since I will need to get a mechanical speed reducer to make the reading in my dash correct. If I screw that inverter in after that, wont it be close for the ecm?

[gregs78cam]

Correct me if I am wrong, but I thought the 4L60E, and 4L80E both put out a 40pp(revolution) signal to the DRAC/VSSB, which converts that to all of the required signals for PCM, Cruise, RWAL, etc. Notice that Pins C7, C12 are inputs and C13 is a 1:1 signal (40ppR) on a single line. What PCM are you using? Can you set the Flag "Vehicle Speed Not From DRAC"? If so then you don't need the DRAC/VSSB and can send the 4Kppm directly from the sensor to the PCM.

[buddrow]

Greg, i believe your theory should work. But be prepared for smoke just in case ;)

[dale]

My understandings from reading the lovely web, was that it was 40ppm tell they went to the 4l60e, then it changed... and that's what I cant find.

Also, that whatever pcm I am using(I forget at the moment) could take a 2000 strait from a vss (assuming axle, tire, gear ratio, etc etc did provide a true 2000).

[buddrow]

The vss reluctor has 40 teeth(4L60E & 4L80E). I dont know of any obd1 pcms that take the vss signal directly from the sensor as they are PM generators which produce an AC voltage. 88-90ish sent vss to instrument cluster where the calcs were done and then sent to the ecm. Now i could be wrong and I am always open to construcive criticism so dont take what i say as gospel.

With the being said, if the sensor/adapter at the t-case diven gear produces 4kppm as Greg mentioned, in theory the computer should be able to accept it.

[gregs78cam]

When I swapped the TBI into my '74 truck(T350/NP203), I made a 40 tooth ring for the T-case front output flange. I fed that signal to a DRAC, and then fed the proper output to the '7427 PCM. If you still had a tail housing and stock sensor location this is what you would do.

Later I was able to find an early '90s Suburban/Blazer instrument cluster, added the optical sensor to it, and ran that signal directly to the PCM on pin F13. Then set the flag at $5D02 bit 4,"Output Speed Not From DRAC", this eliminates the need for the DRAC, and sends a 2Kppm signal to the PCM (if your cable is properly calibrated to 1000revs/mile). Notice that pins C11, C14, C15 are all 2Kppm?

[buddrow]

Thought I was the only one who went thru that much trouble on projects Greg lol. I almost suggested similar but didnt want to complicate things ;)

[dale]

This 95 System goes strait to the VSSB. Then it splits off from there to cluster, ecm, crusie, abs.

[gregs78cam]

Yes with an electronically controlled automatic it should.