Where does speedometer get its info from?
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From: Bartlett Illinois
Re: Where does speedometer get its info from? (Justme)
Can anyone tell me if the speedometer gets info straight from the vss or if it gets info from the ECM. What exactly is a buffered signal?
The VSS sends the 4K pulse per mile signal to the Digital Cluster. the Cluster then divides the signal in half (2K pulse) and sends it to the ECM. This should be the same for 85-89..
90-96 the VSS sends the 4K pulse per mile signal to the CCM/BCM (Central Control Module/Body Control Module) name changed in 1996 from CCM to BCM. from there the CCM/BCM sends the data to be displayed on the LCD panel of your Cluster.
[Modified by -=Jeff=-, 11:15 AM 8/2/2002]
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From: Amarillo TX
Re: Where does speedometer get its info from? (-=Jeff=-)
I am repinning to convert to 730 ECM and wasn't sure if the speedo would read what the vss sends it or the ecm sends it. If the ecm can be changed for different gear ratios and stuff will it change the speedometer output too?
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From: Bartlett Illinois
Re: Where does speedometer get its info from? (Justme)
I am repinning to convert to 730 ECM and wasn't sure if the speedo would read what the vss sends it or the ecm sends it. If the ecm can be changed for different gear ratios and stuff will it change the speedometer output too?
Also the 7730 will not compensate for gearset changes, you will have to change the Drive gear, Driven Gear, and possibly the VSS.
http://www.corvetteforum.net/c4/vett...Gearshtm.shtml
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From: Amarillo TX
Re: Where does speedometer get its info from? (88_vette)
What exactly will the (Instrument Panel VSS Pulse Divisor) and the (Road Speed Constant) change in the ECM Constant Table? I was under the impression that they could be changed for gear changes snd such.
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From: Bartlett Illinois
Re: Where does speedometer get its info from? (Justme)
I never messed with those.. you may want to ask on the http://www.thirdgen.org board.. they may know
Melting Slicks
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From: Murrysville PA
Re: Where does speedometer get its info from? (-=Jeff=-)
Actually, you can use the VSS signal right from the cluster if you change the VSS type in the prom on the 730 if that is what you are using. Very easily done. That's how mine is set up with no problems.
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From: Amarillo TX
Re: Where does speedometer get its info from? (89vette)
How do I change the VSS type and what do I change it to in the 730 ECM? My problem is that I just swapped in a turbo 400 and it has no speedometer gear in it at all (right now) for me to baseline from. I bought a speedometer cable to VSS adapter from stealth conversions but I am fixing to buy the speedo gear for the turbo 400 and need to know how accurate I need to be when choosing the right ratio.
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From: Amarillo TX
Re: Where does speedometer get its info from? (Justme)
How do I change the VSS type and what do I change it to in the 730 ECM?
Which VSS adapter should I buy for my car to still have use of the speedo and not have any trouble with the ECM?
Here is info on http://www.jagsthatrun.com/Pages/Spe...eedometer.html
1. The two-pulse (2000 pulses per mile) square wave (D.C. current or direct current) used on all TBI engines through 1992, all computer-controlled-carbureted engines, and on 1985–1989 TPI engines.
2. A four-pulse (4000 pulses per mile) sine-wave (A.C. current or alternating current) signal is required by the 1990–1993 TPI, 1992–1993 LT1 engines, and 1990–1993 Camaro 3.1/3.4 V6 engines.
Which VSS adapter should I buy for my car to still have use of the speedo and not have any trouble with the ECM?
Here is info on http://www.jagsthatrun.com/Pages/Spe...eedometer.html
1. The two-pulse (2000 pulses per mile) square wave (D.C. current or direct current) used on all TBI engines through 1992, all computer-controlled-carbureted engines, and on 1985–1989 TPI engines.
2. A four-pulse (4000 pulses per mile) sine-wave (A.C. current or alternating current) signal is required by the 1990–1993 TPI, 1992–1993 LT1 engines, and 1990–1993 Camaro 3.1/3.4 V6 engines.
Melting Slicks
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From: Murrysville PA
Re: Where does speedometer get its info from? (Justme)
Well this might not make any sense to you because I do not know to explain it very well. In my 89, I had to disable the mag VSS signal and specifiy an optical signal. GMEPro allows me to do this easily. There is also a way to do it if you have a hex editor. I know what you are saying about the different VSS sensors. I can tell you that a VSS for an 89 Corvette set up like the way I said will work correctly. The speed displayed in the ECM read via Diacom, matches the speed displayed on the cluster. If you use the 90vette bin, you have to change the VSS setting.
HTH
JN
HTH
JN
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From: Amarillo TX
Re: Where does speedometer get its info from? (89vette)
So when you go from a 165 ECM to the 730 ECM the vss signal is still going to the cluster first and then being sent to the ECM right. I thought the later TPI ECM's looked for a 4000 PPM ac current instead of the 2000 PPM dc current the earlier TPI ECM's looked for. Is that what a buffered signal is? Sorry for the wasted space, I just don't want to buy the wring VSS adapter.
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From: Bartlett Illinois
Re: Where does speedometer get its info from? (Justme)
So when you go from a 165 ECM to the 730 ECM the vss signal is still going to the cluster first and then being sent to the ECM right. I thought the later TPI ECM's looked for a 4000 PPM ac current instead of the 2000 PPM dc current the earlier TPI ECM's looked for. Is that what a buffered signal is? Sorry for the wasted space, I just don't want to buy the wring VSS adapter.
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From: Amarillo TX
Re: Where does speedometer get its info from? (-=Jeff=-)
Ok thanks. I believe it is pin BC6 on 730 ECM and A10 on the 165 harness I wanted to make sure it was a 2000 PPM input on the 7730 though. And that is 2000 PPM DC current too right? Thanks again.
Drifting
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From: Gloucester Va
Re: Where does speedometer get its info from? (Justme)
Justme,
Here it is in a nut shell. I just went through the samething you are going through. I had no speed reg. on my Datamaster software after the 165 to 730 swap. I use tuner cat, and all I had to do was un "X" (or take the "X" out of the mag. VSS box in the switchs area.) I already had the 165 A10 to 730 BC6 wired up. Everything works great now.
Here it is in a nut shell. I just went through the samething you are going through. I had no speed reg. on my Datamaster software after the 165 to 730 swap. I use tuner cat, and all I had to do was un "X" (or take the "X" out of the mag. VSS box in the switchs area.) I already had the 165 A10 to 730 BC6 wired up. Everything works great now.
Melting Slicks
Joined: Aug 2000
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From: Murrysville PA
Re: Where does speedometer get its info from? (88_vette)
Yes BC6 is the correct pin. I cannot verify that by un "x" ing the box in tunercat will do the trick. I thought that was just so you don't get a code 24 when there is no VSS signal. In other words, you may have no VSS signal but you won't know it. 88_vette, when you read your scanner does it display a speed? I found it necessary to change the VSS in the chip with GMEPro to get it to work right. My car will stall at every stop without a VSS signal.
So the bottom line is that you need a 2000 pulse VSS signal. Wire it to your exsisting wires so your speedo works. Plug the VSS wire into BC6 and set up the prom to recognize the buffered signal. If you can't set it up, email me your bin and I'll change it for you.
Thanks
Jason
Jason
So the bottom line is that you need a 2000 pulse VSS signal. Wire it to your exsisting wires so your speedo works. Plug the VSS wire into BC6 and set up the prom to recognize the buffered signal. If you can't set it up, email me your bin and I'll change it for you.
Thanks
Jason
Jason
