Will I need a new tune??
 

My first post but I know some of you from other forums. Anyway on to my issue.

First the truck info/bolt-on mods I've done so far.

97 XL 4.2L V6 4r70w 3.08 Non LS, General Grabber UHP 265/70r16s, AF1 CAI, ASP UDP, Cherry Bomb Vortex SIDO catback, Maggie Hiflow Cats, Troyer tuned 94 performance.

Now the issue I have is after lowering the rear 2" with drop shackles the truck has developed a very slight bouncy feel. Had them check the pinion angle and it's only 0.5 degrees off which is ok. My mechanic took off the inspection cover of the rear diff and the spider gears badly pitted, one even has a visible crack and they have waayyyy too much play in them. I was hoping to put this mod off until next year but seeing that crack makes me nervous. So I've ordered a Tru-Trac LS and 3.73 gears.

My question is since my Troyer tune was made for the 3.08s & open diff will I need to get a new tune or could I make the changes with the Xcal3? I'd normally stick with the same tuner but I don't want to drive 10+ weeks with the wrong tune.

I am not to familier with the xcal3 but it should have a "custom option" menu where you can change the gears and save the change with out effecting the custom tune.
If you have the manual it should tell you in there.

Lars

These are the only things it will let me change.


Global Spark
WOT A/F
Rev Limit
Idle Speed
WOT Shift
Shift.

There's very limited things you can mess with for the 97s.

Then I have to say you DO want new tunes. Sorry!

With the new gears your speedometer and odometer will be "off", which is no HUGE deal, but your shift points aren't right either. They're commanded by a combination of speed and throttle position. So, since the truck's speed is wrong, they happen at the wrong time.

I'm sure it's all something you could live with, but I imagine you tuned your truck for a reason, and that reason is not "halfway performance".

But, I've just had a thought, which may negate everything I've said above. Your truck MAY have a more "direct drive" if that makes any sense from the speed sensor to the speedometer. I'm thinking now that the PCM doesn't even get into the act in your MY truck here, and a tune may not be able to adjust the speed. But, when you get the new axle, they can install different gears on the speed sensor so that it will send correct speed and distance information to - "wherever" (sorry, I'm not really sure how your system works - I know it's not a mechanical cable, but I don't think the PCM controls the speedo.

However, the PCM and the speedo DO get their speed information from somewhere, so all you have to do is make sure that information is correct. If it is, then your tune is fine with the new gears and you won't have any speed or distance errors.

Find out from the shop doing the swap what happens with the speed and distance indications.

- Jack

Yes it looks very limited.


Lars:2thumbs:

Lars, I went back and changed my mind. :shrug: See what I added. And, I think the latter part is more correct. I think this is why he has no speed correction capability with this unit.

- Jack

Oh
So a new gear requires a new speedometer gear to compensate for them?
97xl will have to look for a speedometer gear correction kit.

Lars

Yup! I think that is the RIGHT approach. I vaguely remember reading something about this in the not so distant past, when my brain cells were more active. And, I'd think this would be a trivial addition to a gear mod, wouldn't you? I'd be surprised if the installers of the gears, didn't include it in the work order.

- Jack

They must have let it slip their minds also?
Good catch:1toast:

Lars :2thumbs:

I know I can't adjust the speedo with the programmer, needs to be done by swapping out the VSS gear. Just wondering if I'll need a new tune to make the shift points correct. Last thing I wanna do is go messing with the shifts in the programmer and make things worse. It should be liveable until I can get new tunes. Right now the speedo gear is set for stock tire size of 235/70r16 and since my winters are 255 and summers are 265 it was already off to begin with but that didn't seem to make a difference with the tune(when I had the tune made I put 255s as the tire size on Troyers order form.) Guess I'll just wait till PHP is open again and find out the details.

Thanks for the info.