VSS wire splicing
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Yeah, I'm kinda worried about it. I know that solder should work but I'm still nervous. I don't really have a choice, both the wires got to go to the PCM to control the 4L80-E and both the wires got to go to my 1989 K-1500 for the speedometer (which I want to keep stock) and to my cruise control.
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From: Downers Grove, IL
You can splice in if you must, but I don`t think that is what you want to do. I believe that your speedo and cruise control are looking for a 4000 pulse per mile square wave DC signal. The VSS puts out a 40 pulse per revolution sine wave AC signal. You may have to remove the DRAC box in your truck, but your should be able to connect your speedo and cruise to the speedometer output from the PCM. Have you checked out the Jags that run VSS chapter? Its ch13 and you should be able to download if from their site for free.
On the 89, the speedo is looking for a 4k pulse, but the cruise is looking for a 2k pulse. I'm in the same boat, and was thinking I could use the VSS Bufffer box to control the cruise.
See, the old TBI equipped vehicles didn't come with a very good ecm. It couldn't handle the 4k input from the 700R4. So they had to have a Buffer box to dumb down the signal to 2k for the ECM to process it. It also stepped the signal down for the cruise.
What I was going to try and do, was run the Speedo output from the PCM, to the VSS Buffer box. THe buffer box has an unaltered output, so there is your speedo, then utilize the output for the cruise.
Sounds simple right?
I couldn't get it to work. My *guess* is the buffer box is looking for the actual pulses, across two wires from the actual VSS. Since the speedo is only a one wire output, you don't have the complete curcuit. I tried grounding the one wire, than the other with no luck.
I ended up getting a box to step the signal down, but it didn't work all that great, and the cruise surges for the lack of a better decription. Almost easier to drive without it.
Now I did do some reading about adjusting the cruise signal output in the PCM. The guy who did my baseline tune told me there are some scalers in the HP Tuners for cruise, but you would have to experiment with it. Tough to do off the vehicle ya know?
So perhaps I'll go that route before I go to the yards to do the cruise swap as mentioned in the stickies
good luck
-jason
See, the old TBI equipped vehicles didn't come with a very good ecm. It couldn't handle the 4k input from the 700R4. So they had to have a Buffer box to dumb down the signal to 2k for the ECM to process it. It also stepped the signal down for the cruise.
What I was going to try and do, was run the Speedo output from the PCM, to the VSS Buffer box. THe buffer box has an unaltered output, so there is your speedo, then utilize the output for the cruise.
Sounds simple right?
I couldn't get it to work. My *guess* is the buffer box is looking for the actual pulses, across two wires from the actual VSS. Since the speedo is only a one wire output, you don't have the complete curcuit. I tried grounding the one wire, than the other with no luck.
I ended up getting a box to step the signal down, but it didn't work all that great, and the cruise surges for the lack of a better decription. Almost easier to drive without it.
Now I did do some reading about adjusting the cruise signal output in the PCM. The guy who did my baseline tune told me there are some scalers in the HP Tuners for cruise, but you would have to experiment with it. Tough to do off the vehicle ya know?
So perhaps I'll go that route before I go to the yards to do the cruise swap as mentioned in the stickies
good luck
-jason
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I see GM cruise modules with cable $25 to $30 on ebay... get the one that matches your throttle body and connect up the wires. At that price, I can't see much reason for messing with getting a different cruise system to work.
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The DRAC is built into the gauge cluster so removing it would be improbable. I was hoping the 1989 Cluster and the 1998 PCM would use the same signal pulsage, I guess I'm not that lucky...... Well, I did some searching and I found a universal speedometer signal interface from Dakota Digital. >>HERE<< Would this work?
This is how I'm thinking about wiring this.
You guys think this setup will work?
This is how I'm thinking about wiring this.
You guys think this setup will work?
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Your wiring won't work the way you have it drawn up. The DD box needs to be inline with the gauge cluster instead of the pcm. The pcm can understand the vss signal, but the cluster can't.
LS1MCSS is correct
If your diagram is correct, then it seems the Cruise gets its signal from the back of the cluster?
Is your speedo cable driven? If it is, you'll have to find a different box that will be driven by the PCM. I don't think you'll have any other issues though with the cruise as it gets its pulses from the cable driven speedo.
Rodder The cruise worked perfect in the car before the swap. All that needs to be done is to step, or half the signal down from 4k to 2k ppm. Seems a lot easier than buying more parts, running more wires and the like. All the parts are there to make it work, its just getting the correct signal, which appears to be controlled by the PCM. Just like the Tach in the older vehicles. Instead of using a new tach, just change the setting in the PCM.
-jason
If your diagram is correct, then it seems the Cruise gets its signal from the back of the cluster?
Is your speedo cable driven? If it is, you'll have to find a different box that will be driven by the PCM. I don't think you'll have any other issues though with the cruise as it gets its pulses from the cable driven speedo.
Rodder The cruise worked perfect in the car before the swap. All that needs to be done is to step, or half the signal down from 4k to 2k ppm. Seems a lot easier than buying more parts, running more wires and the like. All the parts are there to make it work, its just getting the correct signal, which appears to be controlled by the PCM. Just like the Tach in the older vehicles. Instead of using a new tach, just change the setting in the PCM.
-jason
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LS1MCSS is correct
If your diagram is correct, then it seems the Cruise gets its signal from the back of the cluster?
Is your speedo cable driven? If it is, you'll have to find a different box that will be driven by the PCM. I don't think you'll have any other issues though with the cruise as it gets its pulses from the cable driven speedo.
-jason
If your diagram is correct, then it seems the Cruise gets its signal from the back of the cluster?
Is your speedo cable driven? If it is, you'll have to find a different box that will be driven by the PCM. I don't think you'll have any other issues though with the cruise as it gets its pulses from the cable driven speedo.
-jason
Well if the cruise gets its signal from the cluster, then you have nothing to worry about.
With my 91 Firebird, the cruise receives the input from the VSS Buffer. Sounds like your buffer is built into the speedo. Wish mine was that simple.
I've only seen that with cable driven speedo's, and wasn't sure what year GM swapped over the trucks. I know that camaro didn't change over to electric speedo until '90. Firebirds changed over in '87 though.
Good luck with that swap
-jason
With my 91 Firebird, the cruise receives the input from the VSS Buffer. Sounds like your buffer is built into the speedo. Wish mine was that simple.
I've only seen that with cable driven speedo's, and wasn't sure what year GM swapped over the trucks. I know that camaro didn't change over to electric speedo until '90. Firebirds changed over in '87 though.
Good luck with that swap
-jason
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Well if the cruise gets its signal from the cluster, then you have nothing to worry about.
With my 91 Firebird, the cruise receives the input from the VSS Buffer. Sounds like your buffer is built into the speedo. Wish mine was that simple.
I've only seen that with cable driven speedo's, and wasn't sure what year GM swapped over the trucks. I know that camaro didn't change over to electric speedo until '90. Firebirds changed over in '87 though.
Good luck with that swap
-jason
With my 91 Firebird, the cruise receives the input from the VSS Buffer. Sounds like your buffer is built into the speedo. Wish mine was that simple.
I've only seen that with cable driven speedo's, and wasn't sure what year GM swapped over the trucks. I know that camaro didn't change over to electric speedo until '90. Firebirds changed over in '87 though.
Good luck with that swap
-jason
So now I don't know how I'm gonna set this up......
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From: Downers Grove, IL
I think I see a solution here, but let me try to figure out exactly what you are doing here.
1. You ahve a LSx motor and PCM?
2. You have a 4l80e....is that a LSx 4l80e and your trying to control it with the LSx PCM or are you also keeping your computer from the old motor to run the trans?
You are looking for a 2000PPM signal for cruise and a 4000ppm for the speedo, is there anything else you are trying to get a signal too??
1. You ahve a LSx motor and PCM?
2. You have a 4l80e....is that a LSx 4l80e and your trying to control it with the LSx PCM or are you also keeping your computer from the old motor to run the trans?
You are looking for a 2000PPM signal for cruise and a 4000ppm for the speedo, is there anything else you are trying to get a signal too??
The DRAC is built into the cluster from 88-90,(91?) The couple of older fullsize trucks that I have done the retrofit in I left the cluster controlling the cruise. Then spliced the high and low speed sensor output heading to cluster direcly to the VSS wiring heading to the new LSX pcm. Neither will ever know they are piggy backed with anything else. The trans shifted correctly, and the vss and cruise functioned perfectly and it did not need adaptors and was pretty straight forward.
If you still have problems after that you can simply bolt in a 93-94 cluster rewire the pigtail on the back and then run the VSS input a single green with a white tracer to the speedo output on your 98 pcm.
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From: Downers Grove, IL
The DRAC is built into the cluster from 88-90,(91?) The couple of older fullsize trucks that I have done the retrofit in I left the cluster controlling the cruise. Then spliced the high and low speed sensor output heading to cluster direcly to the VSS wiring heading to the new LSX pcm. Neither will ever know they are piggy backed with anything else. The trans shifted correctly, and the vss and cruise functioned perfectly and it did not need adaptors and was pretty straight forward.
I didn`t realize that the DRAC was built into the back of the cluster on those years. After I looked at the wiring diagrams above I realized that this truck used a DRAC and I knew that you could recalibrate them since I just did that for my 4.3L chevette.