'88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance Question: What is needed to make the 140 MPH cluster(1988 GTA) work? I seen mention of a VSS buffer and some converter box......??? I dont have the mentioned yellow buffer box, as my car was originally cable drive. My platform(originally): 1985 T/A LB9, auto. 85MPH cable speedo. 6k tach Current platform: 5.7 LS1/T56 140MPH 8k tach I have pulled and repinned the cluster connectors to accommodate the '88 cluster. All the gauges work correctly except for the tach and speedo(neither are reading anything). I was planning on running a wire from..... C1 connector Pin 14(speedometer Pin), Dont quote me because I dont have it in front of me. Anyhow, Run that wire to the VSS output from the LS1 ECU. Then reprogram the parameters as mentioned in five7kid's sticky. Sound good, in the ballpark, or not even the same sport? |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance As long as you hook the speedo wire to the LS1 PCM, then you should be in business. That's what I did with the LT1 when I put it in the GTA. As for the tach, from what I remember reading the LS1 tach goes on a 4cyl signal and is probably why the tach isn't working but I believe there is some way to change that in the PCM. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance Hawks sells a box that should get your stock gauge working. You should hook up the VSS to the PCM if its not already its affects some tuning tables. It will probably run okay without it but you might pull codes |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance SO without the box from hawks , there is no way to get the tach and speed signal ? I thought I read somewhere, the speed and tach signal vis vss comes directly from the LS1 PCM. wire that to the correct pin on whatever gauge cluster ur using it should work. I also read that the earlier LS1's , there was already a wire for these 2 but on the later ones these signals were combined in a databus going to the LS1 cluster. But regardless, the speedo and tach pins should be present on the LS1 PCM.......right ? |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance SO without the box from hawks , there is no way to get the tach and speed signal ? I thought I read somewhere, the speed and tach signal vis vss comes directly from the LS1 PCM. wire that to the correct pin on whatever gauge cluster ur using it should work. I also read that the earlier LS1's , there was already a wire for these 2 but on the later ones these signals were combined in a databus going to the LS1 cluster. But regardless, the speedo and tach pins should be present on the LS1 PCM.......right ? |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance I know u explained a few option here. I just want to clarify I understand this correctly.... Speedo:
Originally Posted by cam-
(Post 4186664)
I just bi-wire spiced into the VSS out at the trans meaning I turned the wire into two leads and fed one to the PCM and one into my speedo and all works well. Tach signal :
Originally Posted by cam-
(Post 4186664)
you can also use HPtuners or equivalent to adjust the signal frequency via tuning it into the PCM itself. On the side note I read some where in my 82 service manual that the stock 82 tach signal is also applied a +12V switched supply. I may be wrong . so dont quote me on it. :thanks: And ya appriciate your patience in explaining this. :thanks: |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance I'd like to know more about this signal frequency as well. My tach isn't working (yet). |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance Hmmm....maybe this (http://www.ls1tech.com/forums/conver...-tach-yes.html) is why. Might be worth the 99 cents to try ;) I'll be trying this first before buying any aftermarket tach or box. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance Does this work with only your Pro Comp ultra lights speedo or can the same concept be applied to Stock 3rd gen electronic speedo ? Are u also using another Pro Comp Tach ? I will be having a guy tune the PCM to get the car running anyway. Can I just wire the Tach out pin from the LS1 PCM to the Tach wire on my stock gauge cluster connector and tell the guy to adjust the signal to a 4 cycle ? (Anywhere I can read more about adj. the tach signal in the LS1 PCM ) I think your on the right track now but if you get the stock GTA tach working without the boost feed post up about it. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance Thanks for the replies. Good Info. BTW, my factory 7k tach(incorrectly mentioned as 6k) worked great with the LS1 PCM. A little bit off but usable. IDLE: the tach read 1050 rpms I did hook the 140 speedo to the PCM. Still no reading. I have a guy in Columbus that does PCM programming(I think HP Tuners) for a reasonable price, out of his home. What should I tell him to double the pulse width for tach, and what for the speedo? Thanks again. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance
Originally Posted by tgscooter
(Post 4187842)
Thanks for the replies. Good Info. BTW, my factory 7k tach(incorrectly mentioned as 6k) worked great with the LS1 PCM. A little bit off but usable. IDLE: the tach read 1050 rpms I did hook the 140 speedo to the PCM. Still no reading. I have a guy in Columbus that does PCM programming(I think HP Tuners) for a reasonable price, out of his home. What should I tell him to double the pulse width for tach, and what for the speedo? Thanks again. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance After some research, it looks like 4000 Pulses Per Minute (PPM) is the magic number for the 140MPH Speedo to read. Next time I get a chance, I'll try some PCM adjustments and report back. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance The output on the LS1 PCM should be already set to 4000ppm. Are you sure that you have it repinned right? My '86 cluster didn't have the provisions for an electric speedo but swapping in a dash harness and cluster from an '89 it worked like a charm, and worked when I put my LT1 in my GTA which has an electric speedo. |
Re: '88 GTA cluster into my '85 T/A with LS1/T56 - need some guidance I just wanted to add that on a +99 LS1 harness, the there is no pin on the C105 conn pin# G ckt#121 on the male side, its only for M6 cars. There is another white wire on pin # H ckt#85 on the A4 LS1 harness thats not required. I popped the rubber stopper off, moved the white wire over to pin # G and connected it to the white tach wire on the 3rd gen harness for Tach. I have not tested it, but from what I am reading I should get some signal. |
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