TBI VSS TO SPEEDOMETER

[DTPar1986]

How do you connect the Vehicle Speed Sensor to a Speedometer in a TBI setup? Im aware it connects to the ECM but how does it connect to the speedometer?
Also where can I find the correct electric wiring diagrams for my specific C1500?

 

[Stokes1114]

What year? Later model tbi ran the vss signal through the drac and the drac dispersed the correct signal for the speedo, pcm, and abs or rwal. The drac is a white box inside glove box by pcm. It can be calibrated with some soldering skills. Earlier models without the drac someone else will have to chime in.

 

[DTPar1986]

To be honest the engine is setup for the latest TBI, but the truck itself is a 96. Did an engine swap from a previous project.

 

[DTPar1986]

To be honest the engine is setup for the latest TBI, but the truck itself is a 96. Did an engine swap from a previous project.

BTW thanks for the much needed info

 

[Ken K]

In a 1997, the speedo get its signal from the vehicle speed sensor buffer. It changes an A/C signal form the VSS speed senor at the tranny, into an analog on/off DC type of signal. Circuit #389 with a DK GRN wire that goes to terminal 14 at the cluster. This signal is shared to the PCM and then to the cruise control module. 1996 is paper service manuals only to cover all systems, but as stated, yours may have a DRAC in a with case next to the PCM. It is called a "Digital Ration Adaptor Controller". It requires change due to tire size or final gear ratio changes to get the correct speedo readout. There is information on the web to help you figure out what to do to make changes for correct speed output. We didn't have many truck at the Buick dealer. Well none.

Calculate a number called the “InputRatio” using the following formula:
InputRatio = 63360 x gear ratio x number of pulses per revolution sent to drac via sensor(most gm are 40 )
Then divide that number by Tire circumference in inches x 128000 .
(63360 is the number of inches per mile) (128,000 pulses per mile is DRAC output to RWAL module in some applications.)

 

[DTPar1986]

What year? Later model tbi ran the vss signal through the drac and the drac dispersed the correct signal for the speedo, pcm, and abs or rwal. The drac is a white box inside glove box by pcm. It can be calibrated with some soldering skills. Earlier models without the drac someone else will have to chime in.

Stokes1114 let me ask u this. Do the 96 and later central port injection trucks have the Drac boxes or what do they use, if you know.

 

[DTPar1986]

In a 1997, the speedo get its signal from the vehicle speed sensor buffer. It changes an A/C signal form the VSS speed senor at the tranny, into an analog on/off DC type of signal. Circuit #389 with a DK GRN wire that goes to terminal 14 at the cluster. This signal is shared to the PCM and then to the cruise control module. 1996 is paper service manuals only to cover all systems, but as stated, yours may have a DRAC in a with case next to the PCM. It is called a "Digital Ration Adaptor Controller". It requires change due to tire size or final gear ratio changes to get the correct speedo readout. There is information on the web to help you figure out what to do to make changes for correct speed output. We didn't have many truck at the Buick dealer. Well none.

Calculate a number called the “InputRatio” using the following formula:
InputRatio = 63360 x gear ratio x number of pulses per revolution sent to drac via sensor(most gm are 40 )
Then divide that number by Tire circumference in inches x 128000 .
(63360 is the number of inches per mile) (128,000 pulses per mile is DRAC output to RWAL module in some applications.)

Can you tell me where the VSS is located in a 1996 Chevy C1500?

 

[Stokes1114]

I believe it's near output shaft on the trans. 4×4 series is on the transfer case

 

[DTPar1986]

I believe it's near output shaft on the trans. 4×4 series is on the transfer case

O im sorry I meant Do you happened to know where the DRAC or VSS Buffer module is?
I dnt know if I told you what Ive done? Give you a quick run down ive put a TBI engine and 700r4 in a 96 c1500. Ive put a painless TBI harness in but I want to use the cluster of the 96 to read like it's supposed to. 1 thing I do need if u know where to find it is the pinouts of the connector right behind the cluster or is there a service manual I can buy with correct diagrams in it. If u can help in any kinda way I would greatly appreciate it.

 

[brianmcb]

O im sorry I meant Do you happened to know where the DRAC or VSS Buffer module is?
I dnt know if I told you what Ive done? Give you a quick run down ive put a TBI engine and 700r4 in a 96 c1500. Ive put a painless TBI harness in but I want to use the cluster of the 96 to read like it's supposed to. 1 thing I do need if u know where to find it is the pinouts of the connector right behind the cluster or is there a service manual I can buy with correct diagrams in it. If u can help in any kinda way I would greatly appreciate it.

In my 1995...the drac box is right under the ecm behind the glove box

95 rcsb, L33 5.3, hot cam, frost tune, 5spd, 4/6