5-Speed 3.1 Turbo Speedo Not Correct

[Invasion1]

well in the Turbo Cutlass i was running about 20-25 kms to slow on the cluster and PCM speed.

Mick on GMPCM helped me solve the issue by modifying the code in the VSS section now my speedo and PCM speed is dead on to what my hand held GPS reads at various speeds.

the only problem is now after changing the IP Pulse Driver to get the cluster accurate im now getting a DTC #24 (VSS Failure)

any thoughs?

[LukeZ34]

You'll have to hook me up with what you changed.. It'd be nice to find out what kind of gas mileage the TGP is getting.  :lol:

[Invasion1]

Sure thing Luke

the stock Road speed constant sensor setting for the TGP is 16027.82 when you look at it in the GMPCM program.

i lowered mine to 11930.0971 and that made the speed the PCM gets from the VSS accurate to my handheld GPS  :wink:

the Datamaster program tells you the speed your PCM thinks its going.

but my dash speedo was still 20 off.....so i lowered the IP Pulse Divisor from stock setting which is 9 all the way to 6.75 and that matched it with the PCM speed and the GPS speed.

so all 3 were reading accurate  :D

but i got a Code 24 (VSS Failure) with it at 6.75 so i posted on gmpcm.com's forum and Mick said to bring it down in SMALL!!! increments to prevent a "An invalid value " and cause a trouble code.

what is your TGP's speedo off by?

mine was 20-25 kms off so i needed a significant change in values...

hope i made sense....if not lemme know

:P

[Invasion1]

Success.....mine reads correct on the cluster and PCM speed

both match the GPS within +/- 1 kmph

im more than happy with that!!

[LukeZ34]

Mine reads 10-15 off at higher speeds, and less at lower speeds.
55 Mph is 70 Mph, I know that much, lol.
I need to get my hands on a cheap chip burner then.. I'd love to get that fixed..

[Invasion1]

this is the burner i have and its more than enough for what we need.

http://www.mcumall.com/comersus/store/comersus_viewItem.asp?idProduct=3081

[TGPilot]

Save yourself the trouble Luke...Let me buy it back from you and you do not have to worry about it. It = the car...not just the chip!! :lol:

One thing with the EPROM guys...you also need a UV (Ultra-Violet) eraser for the EPROM chips. If you change the chip to an EEPROM you can just zap it clear. 8)

What size tires and what tranny are you using on the Cutlass? It most likely won't be as simple as copying your VSS and divider values for the TGP's if you have different diameter tire. But it is a HELL of a good start!

[Invasion1]

I have a 282 Getrag out of a 1989 GP and i have 17's Rolling in the Cutlass (245/45/17)

im sure my settings won't be exact on others but its a place to start from....

[TGPilot]

I have a 282 Getrag out of a 1989 GP and i have 17's Rolling in the Cutlass (245/45/17)

im sure my settings won't be exact on others but its a place to start from....

DEFINITELY!! :turn-l:

[Jeff M]

I have a 282 Getrag out of a 1989 GP and i have 17's Rolling in the Cutlass (245/45/17)

im sure my settings won't be exact on others but its a place to start from....

As for the different tires:

Specification / Sidewall  /Radius  /Diameter  /Circumference  /Revs-Mile  /Difference
245/50-16..../        4.8in...../ 12.8in  ./25.6in       ..../  80.6in  .........../      786        ......../0.0%
275/45-17..../        4.9in...../ 13.4in   ./26.7in      ..../  84.0in  .........../      754        ......../4.3%

Jeff M

[skalor]

I have my IP Pulse Divisor set at 6, and my Road Speed Sensor Constant at 12007.8176.  Granted that's with a getrag 284 but you're values should be close.   8)

[TGPilot]

Ok boys...the TGP is home and time to get things to read correctly. Any help here would be great!

On the TGP...What is the stock Road Speed Sensor Constant value? What is the stock IP Pulse Divisor setting? I am too embarassed to say why I need those values to "start over"...I played with the settings 2.5 years ago and made no changes other than to screw it up!! :wink:

[Invasion1]

Stock TGP code VSS settings


IP Pulse Driver Divisor 9

Hex C0

Road Speed Constant Sensor

PU/MI 16027.82

Hex 00E6


My Modified Setting for Cutlass Turbo with 1989 GP 3.1 282 Getrag

IP Pulse Driver Divisor 6.7

Hex 8F

Road Speed Constant Sensor

PU/MI 11930.09

Hex 0135

I believe your HUD is correct but your cluster may be messed up.......

they both should be the same because there both getting the same signal from the ECM.

thus i would believe the digital HUD would be interpreting the accuratly.

when i did mine i used a GPS and the Datamaster Scan tool to see what the diffrence between the speedo reading, GPS reading and ECM reading.

need to find out what your ECM "THINKS" its going because it will mostlikely differ from the Cluster and ECM speed.

lemme know what you find out and i can help ya out more  :)

[Invasion1]

try my settings and i bet your GPS and HUD will be accurate as well as the ECM speed....

looks like your off the same amount i was.......

[TGPilot]

*edit on recorded #'s!

Ok I am an idiot!

Here are the numbers I am seeing from my trip home today.

Speedo...........HUD............GPS.........all #'s are MPH

90...................63...............81
85...................60...............78
80...................55...............72
75...................52...............69
70...................50...............63
65...................45...............58
60...................41...............53

I did 50 down to 30 on the speedo, but I can not read my writting from driving and watching everything in heavy traffic. :oops:  Will try them again tomorrow. :lol: