I actually do have a question and I really don't know where I would post it anyways. When going from stock to bigger tires and changing gear ratio, do shift points change? It does have a tune but I am curious on how the PCM handles the shift points themselves. I have a dakota digital sgi-5e to install but I do not know whether install it off the VSS high or the output to the cluster. Putting it in front of the PCM should adjust shift points back to the correct spot but I do not know what else is in the equation for that......and is it really even something that is going to be a problem? Went up to 35" tires and gearing change will be 3.42 to 4.10. Below are some of the emails I sent to calibration places and dakota digital. Thanks.
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Joseph,
I’m going to get the opinion of a certain engineer. He’s out for vacation right now when he gets back and responds I’ll let you know what he thinks.
Wes Case
Dakota Digital
www.dakotadigital.comFrom: Laughlin, Joseph
Sent: Monday, July 03, 2017 11:10 AM
To: Wes Case <>
Subject: RE: SGI-5E Universal Signal Interface Unit
So is the low signal input just the ground? So from what I understand, is the only wire I need to cut is C2 Pin 10 purple/white and put the SGI-5 E in between? I believe the attached picture is correct for an 04 envoy. From what I have read a few splice into the VSS high in to the PCM and others in to the PCM output to the cluster. Not exactly sure which one I should do because both ways some have had issues. It could just be them. I would assume the high vss is coming from the back only and wouldn’t calculate correctly in 4wd? How much do the ABS sensors play in this? I will be doing a gear change in a month or so once I find time to swap the rear so I really am unsure how I should go about this because I will have to recalibrate it again and don't know how it will effect shift points. The rear is from an 02-05 so the ABS will be the same.
Joe Laughlin
Electrical Instrumentation Specialist
“Once a Marine, Always a Marine”
From: Wes Case
Sent: Wednesday, June 28, 2017 8:55 AM
To: Laughlin, Joseph
Subject: RE: SGI-5E Universal Signal Interface Unit
Joe,
I think the SGI-5E will work. The speedo and odometer could be fed by different Vss signals from the PCM. If you use the SGI-5E to modify the Vss high signal before it goes into the PCM then I think it should do the trick. I think why the others have failed is if they are modifying settings after the PCM has read the signal. If you correct the signal before the PCM then it shouldn’t know any difference and work correctly.
Wes Case
Dakota Digital
From: Laughlin, Joseph
Sent: Wednesday, June 28, 2017 5:25 AM
To: TechSupport <techsupport@dakotadigital.com>
Subject: SGI-5E Universal Signal Interface Unit
I own a 2004 GMC Envoy I6. In HPT, you can access wheel size, VSS, trans RPM. The problem is, even if you change any of these parameters, the PCM doesn’t calculate the % difference. My vehicle is tuned and the PCM is unlocked but I guess every tune program has the same issue….Now few did successfully get the MPH to reflect correct. I’m not sure how they got it to take but even HPT themselves said it can’t be done. I would prefer not to deal with a dealership and I still plan for another gear change that isn’t supported in the PCM and not a factory option. My question is will your converter also make the appropriate changes to both the MPH and the ODOMETER as well as the shift points? Thanks!
Joe Laughlin
Electrical Instrumentation Specialist
“Once a Marine, Always a Marine”
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Heres emails from a calibration shopTapping the output after the PCM would change the signals going to the cluster after all calculations are done by the computer and sensors and is where I would try first As long as your computer isn't doing a sin wave to square wave conversion at the PCM, then that would be the best place to do it. If you go that route and have issues with readings or it starts acting weird, tapping the vss out line from the transmission would be my next recommendation to try. The wiring systems vary wildly on these vehicles year to year so it almost always ends up being trial and error on where to splice the line.
Joe Butera
Beach Calibration
On Jul 3, 2017 12:06 PM, "Laughlin, Joseph" <> wrote:
Everything works fine its just off. I haven’t done anything to mine, its just from what I have read from other peoples experience in the 02-05 models. Some splice into the VSS high in to the PCM and others in to the PCM output to the cluster. Not exactly sure which one I should do because both ways some have had issues. I would assume the high vss is coming from the back only and wouldn’t calculate correctly in 4wd? Dakota digital hasn’t replied really and their instructions are so basic it really doesn’t help from the vehicle side. The device is fairly simple. It’s the vehicle that’s stupid.
Joe Laughlin
Electrical Instrumentation Specialist
“Once a Marine, Always a Marine”
From: Joe Butera []
Sent: Monday, July 03, 2017 11:55 AM
To: Laughlin, Joseph
Subject: RE: 2004 GMC Envoy
There are known issues with the instrument cluster on those model year vehicles. If your speedometer is jumping or acting erratic in any ie. Bouncing, not moving smoothly or jittering, or getting stuck at random intervals, you will need to replace the stepper motors in the instrument cluster as well.
Joe Butera
Beach Calibration
-----Original Message-----
From: Joe Butera []
Sent: Thursday, June 29, 2017 10:56 AM
To: Laughlin, Joseph
Subject: RE: 2004 GMC Envoy
Hi Joseph,
I was just reviewing our conversation and noticed that you had said that someone managed to change your speedometer readings and the odometer continued to be off. A ratio adapter box like the sgi-5 will change the readings for both the speedometer and odometer as they should be working hand in hand. They both receive signal from the same sensors and same bus on the PCM. The only place they separate is in the cluster itself. Prior to the installation of one of these adapters, I recommend reversing the modifications that have been done and getting a fresh accuracy measurement.
The best way to get a measurement for one of these boxes is to use a GPS or any other distance measuring device that calculates distance to the 1/100 of a mile and drive exactly one mile on the vehicle odometer. The total distance traveled on the other device will be your ratio that would get programmed into the adapter to set everything correctly.
Joe Butera
Beach Calibration
-----Original Message-----
From: Laughlin, Joseph []
Sent: Wednesday, June 28, 2017 8:32 AM
To: Joe Butera <>
Subject: Re: 2004 GMC Envoy
Thank you sir
Sent from my Verizon Wireless 4G LTE DROID
Joe Butera <> wrote:
Dakota digital sgi-5 is one brand of adapter that will do the job for you
Joe Butera
Beach Calibration
On Jun 28, 2017 7:36 AM, "Laughlin, Joseph" wrote:
Are you referring to something like a Dakota Digital SGI-5E? I ordered that but then canceled it. I didn't know if it would adjust the odometer as well. I was seeing if I could get the PCM itself changed but its still looking like I will need to add the convertor.
Joe Laughlin
Electrical Instrumentation Specialist
Atlantic Plant E&I Shop
"Once a Marine, Always a Marine"
From: Joe Butera []
Sent: Wednesday, June 28, 2017 7:22 AM
To: Laughlin, Joseph
Subject: Re: 2004 GMC Envoy
An aftermarket electronic ratio adapter can be installed to modify the VSS signal prior to reaching the PCM which will change how the speedometer/odometer read. We do not do the installs in house, but have a shop down the road that can install these parts once the correct ratio is known. Give me a call anytime today after 9AM at the number below and I'd be glad to assist you in getting your issues taken care of.
Joe Butera
Beach Calibration
On Jun 28, 2017 6:41 AM, "Laughlin, Joseph"
wrote:
I own a 2004 GMC Envoy I6. Apparently GM had another terrific idea with the
I6 gmt360s from 02-05. It is a class2 bus but for some reason GM didn't put in the conversion or something that interfaces with the speedo and odometer(problems with ABS happen occasionally). In HPT, you can access wheel size, VSS, trans RPM. The problem is, you can change the wheel size and it does visually but the PCM doesn't do any adjustment calculations. You can physically go out and measure the rotational circumference and do the math to get the correct variable to put in the VSS/Trans RPM. Once again the PCM doesn't use the numbers and keeps the original but will show your change. My vehicle is tuned and the PCM is unlocked but I guess every tune program has the same issue..Do you use a tech 2 and are you able to make a wheel size change(not a factory size) and a gear ratio change(a ratio that GM uses and should have the selection)? Thanks
Joe Laughlin
Electrical Instrumentation Specialist
"Once a Marine, Always a Marine"