VSS questions for 91 GM TBI to ecm and VSS to speedo need answers???

[slizammed18]

I need ecm VSS info. My truck is a 68 GMC 1500 Long Bed . I'm running a 91 GM TBI 350 with a painless wire harness(both Chassis and EFI). my trans is an old Muncie SM318 3 speed 8 tooth drive gear on the output and a 20 tooth speedo gear. my axle ratio is a 3.07, im keeping my wheels 15". My Comp is 1227747 as requested by painless's instructions. my VSS is a 2 pulse made by JTR 2 wire (also specified per painless instructions). Im also planning on running Classic Instruments speedo(electric). The couple questions I have are painless want the VSS to connect to the ecm with the 2 pulse square wave sensor(directly). Classic instruments also need a signal from the VSS, but there is no ecm signal output to the speedo or vise versa the only output is in the speedo signal box but I think it changes values for the speedo output so I dont think I can use the same ouput for the speedo and ecm on their speedo box especially if the computer wants 2 pulse square wave. so my big question is can I tie the VSS wire and the speedo wire together at the output of there speedometer box or do I need dedicated wires? can I just tie the 2 together at the VSS? do I need a 4 wire DRAC to solve this problem? lastly being my trans was originally geared for a mechanical gauge cable drive i.e. 8 tooth output gear at trans, 20 tooth speedo gear; newer 90's gm trucks ran about a 40 tooth speedo gear in the 90's so how do I know that I will get the 2k pulse per mile? is there a calculation im lost??? who do I turn to to answer these questions, Im trying to keep this truck simple but its not going so swell. thanks in advance

[myburb]

I had a class instrument speedo in a old chev pick up and a turbo 400 and the speedo had lots of adjustment for input pulses.

[dave w]

Information from Painless TBI Installation Manual: http://www.painlessperformance.com/Manuals/60101.pdf

See attached screen shot.

dave w

[lionelhutz]

You should be able to parallel them.

The sensor will provide 2000ppm IF you have the proper speedometer gears to drive a mechanical speedometer when considering the rear gears and tire diameter. You can find info online for selecting the right gears with a mechanical speedometer. Changing the gears is the only way to adjust the output of the sensor so the ECM will read the correct speed with the setup you are using.

GM has used mechanical speedometers that require the cable to rotate 1000 revolutions for each mile traveled at least from the late 50's until they quit using mechanical speedometers. So, install a pickup that outputs 2 pulses per revolution where the cable goes and you will get 2000 pulses per mile traveled.

Since you can program an electronic speedometer I would check that the ECM speed is reasonably close and then program the speedometer so it's very accurate. You're not running a lockup converter or an electronically shifted transmission so there really isn't a need to get the ECM speed exactly bang on.