04 GTO Tune Speedo Fix
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I'm currently running a LQ4 with a cable throttle body in my 1995 Impala SS. I'm also using a gauge cluster out of a 1995 Chevy Camaro. Since I've done my swap, my speedometer is showing 2.5x what my actual speed is (verified via HPTuners and GPS). I emailed HPTuners about this, and the answers they provided didn't really assist in solving the problem. As these engines are becoming more and more plentiful, I took it upon myself to find out why my speedometer is reading so high, so others wouldn't have the same problem.
I decided to toy around with the EFILive Demo and see what I could find. While digging around in the Speedo tables in EFILive, I found out some very interesting Information, and the cause of my speedometer reading higher than what it should. There is a setting under Speedometer, that says PCM Primary Pulses per KM output Rate: It states this is what the PCM outputs for J2 Pin 50 for the PCM, which is one hooked to my speedo. This controls what output rate (4000ppm which is actually 3999.22) the PCM uses for the cluster and cruise control.
Looking at the 2004 GTO A4 tune in EFIlive, it shows the PCM Primary pulses/KM output as 6226;
![](http://i5.photobucket.com/albums/y194/hitman09112171/LQ4%20Swap/EFILive04GTO.jpg)
but yet in a 2004-05 CTS-V it shows it as 2485;
![](http://i5.photobucket.com/albums/y194/hitman09112171/LQ4%20Swap/EFILive05CTS-V-1.jpg)
as it does a 2000 Silverado A4, 2002 Corvette Z06, 05 Silverado, and so on. A difference of about 2.505x, which would explain why the speedometer reads so high. I guess the GTOs were the GM oddballs when it came to PPM outputs. The only way I have found to fix this is to find a tuner with EFILive and have them change the parameter, as HPTuners doesn't have this feature. Some associates and I have emailed HPTuners support to try and get them to add this to the next release, but only time will tell how that works out.
I have yet to fix mine, because I use HPTuners, so I need to find a Tuner willing to flash my tune to a PCM with HPtuners, change it with EFILive, and read it again with HPTuners. Oh joy
I decided to toy around with the EFILive Demo and see what I could find. While digging around in the Speedo tables in EFILive, I found out some very interesting Information, and the cause of my speedometer reading higher than what it should. There is a setting under Speedometer, that says PCM Primary Pulses per KM output Rate: It states this is what the PCM outputs for J2 Pin 50 for the PCM, which is one hooked to my speedo. This controls what output rate (4000ppm which is actually 3999.22) the PCM uses for the cluster and cruise control.
Looking at the 2004 GTO A4 tune in EFIlive, it shows the PCM Primary pulses/KM output as 6226;
![](http://i5.photobucket.com/albums/y194/hitman09112171/LQ4%20Swap/EFILive04GTO.jpg)
but yet in a 2004-05 CTS-V it shows it as 2485;
![](http://i5.photobucket.com/albums/y194/hitman09112171/LQ4%20Swap/EFILive05CTS-V-1.jpg)
as it does a 2000 Silverado A4, 2002 Corvette Z06, 05 Silverado, and so on. A difference of about 2.505x, which would explain why the speedometer reads so high. I guess the GTOs were the GM oddballs when it came to PPM outputs. The only way I have found to fix this is to find a tuner with EFILive and have them change the parameter, as HPTuners doesn't have this feature. Some associates and I have emailed HPTuners support to try and get them to add this to the next release, but only time will tell how that works out.
I have yet to fix mine, because I use HPTuners, so I need to find a Tuner willing to flash my tune to a PCM with HPtuners, change it with EFILive, and read it again with HPTuners. Oh joy
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Last edited by GA95DCMSS; 05-03-2012 at 09:47 AM.
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thank you. you just totally answered my question, although my actual info search was to find out if the ppm output to the speedo could be changed although i want to change mine to 16000 ppm to avoid the need to purchase an additional adapter for my aftermarket speedo.
info is power.......
info is power.......
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I had the same issues with my 04 gto motor in my monte. Went back and forth with John at Speartech, he did my GM harness and Ecm programming. I am using an autometer speedo. Had to settle for a dakota digital box to convert pulses. Aftermarket guage is more forgiving because u can just do a 2 mile run and hit button and it will self calibrate
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thank you. you just totally answered my question, although my actual info search was to find out if the ppm output to the speedo could be changed although i want to change mine to 16000 ppm to avoid the need to purchase an additional adapter for my aftermarket speedo.
info is power.......
info is power.......
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No problem guys, I'm glad it finally helped someone. HPTuners does support adjusting the PPM now, you just have to email support and have them send you the latest beta. It'll be under the speedometer tab (of course).
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#10
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Calibrating the aftermarket gauges are one thing but you still need to get the OS set up correctly. As far as I remember the pulses on the 04 GTO are 4000 but I will have to go back an check. If you are running an automatic trans you will need to fix the calibration or it will be off on the shifting. When I calibrated my speedo I used my iPhone to go 2 miles. My pulses were off by 1 when it said 2 miles. I believe if you guys go into the tools there is a conversion routine that will set the shift parameters, etc for all 3 tuning tools. TC was spot on for me.
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Calibrating the aftermarket gauges are one thing but you still need to get the OS set up correctly. As far as I remember the pulses on the 04 GTO are 4000 but I will have to go back an check. If you are running an automatic trans you will need to fix the calibration or it will be off on the shifting. When I calibrated my speedo I used my iPhone to go 2 miles. My pulses were off by 1 when it said 2 miles. I believe if you guys go into the tools there is a conversion routine that will set the shift parameters, etc for all 3 tuning tools. TC was spot on for me.