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Thread: GMC Envoy Speedo

  1. #1
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    GMC Envoy Speedo

    (Sorry - newbie) I have a 2004 GMC Envoy with the I6. After running VCM Suite 2.2.0 and going to the speedo options, I cannot modify tire size. I onyl get a few options (4 to be exact). These options are: VSS Pulses per Mile, VSS Trans Revs per Mile, FInal Drive Ratio - Drive Sprocket Ratio, and Trans Revolutions/mile). I tried all of these and none of them seem to adjust my speedometer. Any help would be great!

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    Quote Originally Posted by wstaylor
    (Sorry - newbie) I have a 2004 GMC Envoy with the I6. After running VCM Suite 2.2.0 and going to the speedo options, I cannot modify tire size. I onyl get a few options (4 to be exact). These options are: VSS Pulses per Mile, VSS Trans Revs per Mile, FInal Drive Ratio - Drive Sprocket Ratio, and Trans Revolutions/mile). I tried all of these and none of them seem to adjust my speedometer. Any help would be great!
    Hopefully there's a 'tire revolutions per mile' setting ? That's the only one to modify. Don't touch drive ratio, sprocket ratio, etc...

  3. #3
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    There is no tire revolutions per mile. In fact, 90% of the information on the help pages is not there. There HAS to be some way I can change it... Does anyone have a suggestion?

  4. #4
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    Just to let you know im looking into it for you.
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

  5. #5
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    Thanks! Let me know what you find!

  6. #6
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    I too am having the same issues with not being able to change any parameters. Any luck with a solution?

  7. #7
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    ahh the good old days... I remember when trying to dial in my tires with my '02 trailblazer.. seems to be only the newer pcm I6s are able to change tire sizes... only way you'd be able to do it is with Tech2.

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    Sorry to bump an old (ancient) thread, but I can't seem to find any newer information on this topic. I see that foff was going to take a look at the issue, but it doesn't appear that any changes have been made to the speedo tab since then. For reference, I have a 2004 Trailblazer, which should be exactly the same setup as OP's vehicle.

    From my experimenting today, I started by adjusting by my change in tire size... 3.74% larger tires, so I multipled the stock values by 0.9626.

    If you change only 'VSS pulses per mile', the dash speedometer will be correct.

    If you change everything but 'Drive sprocket ratio' (leaving this value at 1.000), the HPT gauges will be correct, but the dash speedometer is wrong.

    Oddly, I found that setting the 'Drive sprocket ratio' to 1.037(4) and leaving all other values at stock, it appears that my dash, HPT, and the GPS all agree at 65mph -- within reason. My GPS tended to wander between 64-67, but generally settled right around 65. I still need to try a mileage test on the interstate to confirm if everything is as close as it appears.

    So now I'm wondering... did I just happen to stumble on a solution to the problem? Have changes been made to the editor that allowed this to work now when it didn't before? And most importantly, will changing the drive sprocket ratio adversely affect anything else that I should be worried about?

    [EDIT] Nope, I was wrong. Got out on the highway at cruising speeds with the GPS and could see that in fact my speedo is still off by the same amount. I was hopeful there for a moment.
    Last edited by Shdwdrgn; 04-10-2013 at 05:04 PM.

  9. #9
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    bump, any updates to this matter?

  10. #10
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    Not directly. Due to changing my axle gears last Fall I acquired some new data that I sent to the HPT team. They gave me an update to see if the new information could be changed, but unfortunately it still had no effects on the speedo. So far it looks like if you want to recalibrate for a tire size, going to your dealer (or someone with a Tech-II programmer) is still the only option.

    One this I did discover, however... If you change your gearing, you can grab a tune file from another vehicle that has the same gears, and when you write it to your PCM it will update your system, including the speedo. I have stock tune files for the 3.42 and 4.10 gears, and I'm sure someone else could come up with a file for 3.73's, so at least that option exists with HPTuners.
    2004 Chevy Trailblazer I6 + CAI

  11. #11
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    Thanks for the reply Shdwdrgn. Sucks being an older platform as we are probably at our limits of what is going to be unlocked by hptuners as they are most likely going to be focusing on the larger newer platforms for updates and tunes.

  12. #12
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    Trailblazer Speedo Problem

    Shdwdrgn?
    Sorry to bring back the past, but did this work for you? Im having the same issue now. no support from Hpt.....
    Changed my gears to 3.42 from 3.73 and cant figure out what Vss's to change. Got a map from another guy with factory 3.42, and copied the map but everything is still off. not to mention all the trans stuff changed too. Completely different... different trans maybe. I dunno

  13. #13
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    Yep, flashing with a copy of the tune file from another vehicle with the same gearing has worked perfectly since that time. Basically I had to grab a stock tune file and manually copy all the changes I had previously made into the new tune. Note that changes to the shifting stiffness will need to be pulled WAY back. The first time I put it in 4LO I thought I was going to drop the transmission because it shifted so hard. However if memory serves, all the other tuning changes I had previously made (including my shift points) all transferred smoothly to the new gearing. Sorry I don't actually have a file for the 373 gear, but if you ask on gmtnation.com a lot of folks there play with their tunes and can probably provide a stock file for you.

    I'm curious, if you went to all the trouble and changing your gears, why didn't you go to 410's? I mean, my tires are only 1" larger than stock so they don't make much difference in the gearing, but I absolutely love my 410's for everyday use.
    2004 Chevy Trailblazer I6 + CAI