Is it worth changing gears for better MPG's???

[moondoggie]

Good Day!

"I used a commercial VSS re-calibrator to modify vss signal only." Could you be more specific? Jim doesn't mind at all if we mention product names, as long as we're not hawking them.

Hacking the VSS signal looks like it would NOT be a resistor or pot situation - from a quick glance, that signal is a frequency that would have to be multiplied or divided to hack (clarification please).

Blessings!

(signature in previous post)

[TurboDiverArt]

Art, I'm thinking closer to 45mph for od/lockup w/4.10's. I also think using cruse control locks converter too.

Tire width does effect milage, but tread pattern plays bigger role the MT/R's I used made mpg suffer, the SilentArmor is more road friendly and quieter so not as bad.

Your vss is on the t-case along w/2 other speed sensors, 1 for the front drive shaft, 1 for the rear driveshaft. I just discovered the "vss" hack works a little while ago.

Hacking the speed signal from the vss to the vssb will correct the speedo only and leave the 3.73 shift/lockpoints you have now.

Hacking the vssb you modify speedo, shift/lockup to higher mph setting, abs, cruse control. TheDieselPage sells the book showing the hack of VSSB.

I used a commercial VSS re-calibrator to modify vss signal only.

Getting accurate on speedo calibration comes w/hack either way, especially if you measure tire diameter and use this measurement in re-cal.

That

[TurboDiverArt]

Hacking the speed signal from the vss to the vssb will correct the speedo only and leave the 3.73 shift/lockpoints you have now.

Hacking the vssb you modify speedo, shift/lockup to higher mph setting, abs, cruse control. TheDieselPage sells the book showing the hack of VSSB.

OK, reading into your post a little more.

Assuming that from a calibration standpoint the 4.10 VSSB setting does not affect mileage in itself or general health/management of the engine and drive train. Would it make sense, or is it even possible, to set the VSSB to 4.10

[DA BIG ONE]

Good Day!

"I used a commercial VSS re-calibrator to modify vss signal only." Could you be more specific? Jim doesn't mind at all if we mention product names, as long as we're not hawking them.

Hacking the VSS signal looks like it would NOT be a resistor or pot situation - from a quick glance, that signal is a frequency that would have to be multiplied or divided to hack (clarification please).

Blessings!

(signature in previous post)

Ok, It is called and "electronic ratio adapter" (ERA) from ABBOTT ENTERPRISES, INC. Just use your divide ratio between changes match it the switch settings (micro-rockers) and your goos to go.

www.abbott-tach.com or www.atrol.com

[TurboDiverArt]

Ok, It is called and "electronic ratio adapter" (ERA) from ABBOTT ENTERPRISES, INC. Just use your divide ratio between changes match it the switch settings (micro-rockers) and your goos to go.

www.abbott-tach.com or www.atrol.com

I assume you put this in series? Meaning you cut the signal wire going from the VSS to the VSSB and put the ERA in the middle? That way the VSSB knows the actual speed as modified by the ERA but thinks the gearing is still stock?

Art.

[moondoggie]

Good Day!

Thanks!

Blessings!

(signature in previous post)

[DA BIG ONE]

I assume you put this in series? Meaning you cut the signal wire going from the VSS to the VSSB and put the ERA in the middle? That way the VSSB knows the actual speed as modified by the ERA but thinks the gearing is still stock?

Art.

Yes, that's it.

As for engine management on the 1999 6.5 w/NP246 the vss output signal @ pin C-11 from vssb does not connect to pin F-13 (speed signal) @ pcm.

[DA BIG ONE]

JET makes a re-calibrator SCU-2000 that hacks vss only, in a recent e-mail to them I asked if it will function w/NP246, they replied yes.

Their unit plugs into harness at t-case then requires modual to be installed into vehicle.

[TurboDiverArt]

Yes, that's it.

As for engine management on the 1999 6.5 w/NP246 the vss output signal @ pin C-11 from vssb does not connect to pin F-13 (speed signal) @ pcm.

Just for my own clarification. There are two computers at play, right? The PCM that controls the drive train and the ECU that controls the engine? If correct, any idea which each uses the speed signal for and why? What's the VSSB feeding then if not the PCM? Only the gauges?

Sorry for so many questions but I think it's an interesting topic and conversation.

Art.

[ronniejoe]

The PCM or Powertrain Control Module controls both the engine and the transmission (and senses engagement of the front differential). Therefore, it controls the entire powertrain of the vehicle. It's one box. There is no ECU or ECM separate from the PCM.

[TurboDiverArt]

The PCM or Powertrain Control Module controls both the engine and the transmission (and senses engagement of the front differential). Therefore, it controls the entire powertrain of the vehicle. It's one box. There is no ECU or ECM separate from the PCM.

I didn't know that, thanks!! For some reason I thought there were two computers in play. So, when you upgrade to a Heath or other computer, it's the PCM you are upgrading?

This begs the question, if the PCM is not getting speed from the VSSB as stated above, where does it get it from? I'd think it would care for management of the transmission, cruise, etc.

Art.

[ronniejoe]

Actually, it does get it from the VSSB. I'm not real sure I understand everything stated earlier in this thread.

[DA BIG ONE]

Actually, it does get it from the VSSB. I'm not real sure I understand everything stated earlier in this thread.

Hello RJ, I'm by not means an expert, but this is what I've found when hacking VSSB. When switching gears, or changing tire sizes hacking vssb to correct speedo also changes shift/lockup points by the same %. However, if the vssb is not hacked and only the vss is then speedo is corrected but the shift points/lockup all stay at the points they were before the gear/tire change.

[DA BIG ONE]

My burb came w/4.10's when I changed out the gears to 3.42's I hacked the vssb the speedo then the shift/lockup points all changed the same % of the change ratio w/od/lockup at 60+- mph.

I rehacked the vssb to the original 4.10 setting "even though I still have the 3.42'2 and then hacked the vss to correct the speedo, the result was quicker shift/lockup points w/od/lockup at 45+- mph.

The vssb on the 1999 diesel burb I have does not include the C-11 (VSS) pin hookup connected to the F-13 pin @ PCM, not sure if this is because of the AutoTrac, or?

So, If one has a 3.73 gearset then hacks the vssb to think there are 4.10's then hacks vss to correct speedo, the shift/lockup points will be closer together, go the other way and the shift/lockup points will be farther apart.

[DA BIG ONE]

I didn't know that, thanks!! For some reason I thought there were two computers in play. So, when you upgrade to a Heath or other computer, it's the PCM you are upgrading?

This begs the question, if the PCM is not getting speed from the VSSB as stated above, where does it get it from? I'd think it would care for management of the transmission, cruise, etc.

Art.

@ vss 821 purple/white line "high resistance vss output" to pin C-12 vss input @vssb

@vss 822 lt green/blk line "vss output" to pin C-7 vss input @ vssb

C-8 @ vssb 451 blk/wht body ground

C-9 @ vssb 441 BRN 10 amp power ign on

C-10 @ vssb 690 wht to antilock ABS

C-11 @ vssb output blank but drawings have it going to F-13 of PCM

C-13 @vssb transmission output 437 bwn to F-12 @ PCM transmission output speed (NOTE: I don't know if this is an in or out signal at vssb) surely others may know.

C-14 @ vssb output 817 grn/wht to cruse control

C-15 @ vssb 389 dk grn to speedo

[moondoggie]

Good Day!

Owning two 95 6.5's has been handy. The pickup has 4.10 gears, the Sub 3.42. I noticed the higher shift points on the Sub right away. I'm quite sure the shift points are controlled by shaft rpms (& footfeed position etc), NOT vehicle speed.

As fuel economy is my only hobby, this is of interest. I'd like lower shift points, & even more, an earlier TC lockup in the Sub, more like how the pickup shifts.

This thread has been very profitable for me. It never occurred to me that there was a way to hack the VSS signal - the links provided earlier in this topic show this is readily available. Some day I'd REALLY like to do this to our Sub.

I'll plagiarize a local radio show - you learn more here by accident than anywhere else on purpose. Thanks again, folks, for helping me keep my junk running, & running the way I like.

Blessings!

(signature in previous post)

[JohnC]

.... When switching gears, or changing tire sizes hacking vssb to correct speedo also changes shift/lockup points by the same %. However, if the vssb is not hacked and only the vss is then speedo is corrected but the shift points/lockup all stay at the points they were before the gear/tire change.

I thought we flogged this one beyond death a while back. This may be a semantic argument, but...

Shift points and lockup are controlled relative to (as they should be) the torque curve of the engine as it relates to engine RPM, NOT by road speed. When you change the axle ratio, the shift points do NOT change (relative to engine speed). Hacking the VSSB has no effect one way or the other, except to make the speedo reflect the actual road speeds. What you have accomplished with the double fake is to move the shift points lower on the torque curve, thus maintaining shift points at the same road speed as before but at lower engine speeds. Maybe good for unloaded economy, but wrong for everything else.

Had you purchased the vehicle with the 3.42 gears, the shift points would not be where you have them now.

It is interesting to note that otherwise identical LD and HD chips differ in TCC lockup speed. the HD chip is set about 5 mph higher to allow torque multiplication farther into the power band.

That's my story and I'm stickin' to it...

[TurboDiverArt]

I thought we flogged this one beyond death a while back. This may be a semantic argument, but...

Shift points and lockup are controlled relative to (as they should be) the torque curve of the engine as it relates to engine RPM, NOT by road speed. When you change the axle ratio, the shift points do NOT change (relative to engine speed). Hacking the VSSB has no effect one way or the other, except to make the speedo reflect the actual road speeds. What you have accomplished with the double fake is to move the shift points lower on the torque curve, thus maintaining shift points at the same road speed as before but at lower engine speeds. Maybe good for unloaded economy, but wrong for everything else.

Had you purchased the vehicle with the 3.42 gears, the shift points would not be where you have them now.

It is interesting to note that otherwise identical LD and HD chips differ in TCC lockup speed. the HD chip is set about 5 mph higher to allow torque multiplication farther into the power band.

That's my story and I'm stickin' to it...

If I'm understanding things correctly, I "think" we are all talking the same thing but using different or maybe slightly incorrect semantics. You are definitely correct that the shift point is load and TPS based and not strictly RPM based.

One area I think I'm going to disagree with you on is that the stock shift points are where you want them and that lowering them somewhat is not what you want to do. Yes you hold torque multiplication longer by delaying the shift point higher in the RPM range but torque multiplication is power in multiplied by the gear ratio. So, making the shift point above the max output on the torque curve means less power into the torque multiplication so less power out. Now, you do have to shift higher than the max torque otherwise the bottom of the shift will be below the torque curve and the truck makes no power after the shift. I don

[moondoggie]

Good Day!

"...(as they should be)..." I might drive my truck different than you do, so maybe what you think is best isn't best for me. I'd prefer to help you get your truck where you want it (unlikely - you've forgotten more than I'll probably ever know about these things) & you help me get mine where I want it. If what I want to do with my truck might hurt it, it'd be nice if you'd let me know, however - I'd certainly do the same for you.

"Maybe good for unloaded economy, but wrong for everything else." Well, maybe that's at least one of the things I'd like to try eh?

"I thought we flogged this one beyond death a while back." Is it just possible one of us hit JohnC's hot button? Please take no offense - none intended. Like I said, I need you folks to help me keep my junk running, especially experts like JohnC.

Blessings!

(signature in previous post)

[ronniejoe]

[quote=TurboDiverArt]As the truck increases past about 2800 the truck seems to make less and less power. It's like someone has engaged cruise control. I hit 3400 or so, switch gears, drop below 2800 and she starts pulling again, get past 2800 and the acceleration rate drops. At least by the "seat-o-pants" meter, if I stomp on it, let it get to about 2800-3000 RPM's, let off the throttle a little so it shifts and then increase the throttle (making sure it doesn