Exactly what is going to cause it to hit the rev limiter before it shifts?
Or exactly what about it is going to damage the transmission?

The pcm gets it's speed info from the tailshaft housing mounted VSS, can one of you rocket scientists tell us exactly how the pcm is going to have any clue something changed?

Far as the OBD1 swap where someone lives and if inspection is a consideration needs to be considered before this is discussed.
The if it is determined this is an interesting option $.50 worth of resistors soldered in the pcm is the usually solution to the knock sensor thing, or as Ed Wright has posted turn off the knock sensor code, see item number 4 in his post.
https://ls1tech.com/forums/13617278-post28.html

 

Lets see, the gear ratio changes making the speedo off.. need I continue?

 

Yes I agree it makes the speedo off, BUT the speedo info is based on the VSS which is BEFORE the gear ratio change.

You act like the pcm gets it's info from the tire, if that were the case then yeah you would hit the limiter since the tire is after the point at which the ratio was changed.

 

The shift is speed based, off that sensor yo mention which thinks it has 3.23s behind it.

 

correct the pcm does a calculation off of the pulses it recieves from the vss to determine the mph........yes the vss will turn the same speed however the final number that the computer uses for calculation will be off because of the gear multiplier its using......the speedo will read lower than it actually is going thusly the car may over rev before it tries to shift.........however......there is also a rpm shift point in the computer.....which ever it gets to first it will go by so the car will still shift it will use the rpm points.......his speedo and tcc lockup will be incorrect however

 

and it is the only input the pcm has for speed so it has no idea anything has changed. Like I said for what you propose to be true the speedo would have to be driven by a tire.

You also have not explained the tranny damage you expect.

 

lol this is classic I think I will save this.

Ok lets say the 30% throttle shift from 1st to second will happen at 23 mph, you would have to rev the pee out of it to get there for a simple 1-2 shift, no tranny lock-up at the right time later. A silly person drives around like this over reving the motor , heating up the tranny just on a small daily stroll to work and eventually the accelerated wear catches up to everything. In most cases these are 90 plus thousnad mile vehicles.

 

via math it technically is lol.......just think about it for a minute lol

 

I just read all this over again, and I want to apologize for my condescending additude.

 

This has started a little more discussion than i expected.The gears are goin in thursday.If anyone knows anybody close to southern indiana that does obd2 tunes let me know.I would like to stay with my current ecm for now if at all possible.i know hypertech makes a handheld that will do what i need,but for what it does 400 bucks seems a little steep.

 

Hypertech has been shown to slow cars down at the track, complete junk.
pcmperformance has something that would interest you a do it yourself flash kit that will upload a custom tune they write.

Far as the gear change and shift points without programming do you guys understand what I am saying? The pcm has no idea the actual vehicle speed has changed. If the VSS was on the front tire like my brother's old VW van speedo was then the rev limiter would be a concern.

 

The problem is gears raise the RPM to MPH relation.

5700 RPM in an A4 with 275/40/17 tires is 44mph. With 3.73 it makes it 38mph. Thats a 6mph difference. So say the car is looking for 40mph to shift. Thats 6000rpm when an A4 with 3.73 and a 40/17 tire will hit 40mph.

 

THE CAR DOESN'T KNOW IT IS TRAVELING A DIFFERENT SPEED.

If the pcm were reprogrammed just to fix the speedo but not the shift point then that would be right but we are talking stock programming. So again how does the pcm know the change occurred?

 

i will check into pcmperformance ,thanks for the info

 

You'll be fine your not going to kill the tranny, the shift points will be off like mentioned but not as horrific as other have said.

I've got a 4l60e in my blazer and I went from 3.73's on 31" tires to 4.88's on 35" tires. The speedo just showed faster than what I was actaully going. Only thing that was a bother or problem was the torque converter locking up a little early, for example would lock up at 45mph but when the speedo was showing 45 I was actaully going closer to like 35/40mph so it would lug a little bit. Shift points themselveds were fine though and at wide open throttle it still shifts at 5500rpms just like it did.

Don't get me wrong I would get it tuned but it isn't any life and death deal by any means

 

Are you talking about how the Mph isn't going to be affected because the VSS is going to detect the same amount of speed?

 

If you look in tunercats and every other tuner program I have seen it askes the rear tire size and the rear gear ratio, and then tells by pulses from the VSS how fast it is going, understand now, the math is a 3 part equation, change even 1 part of the equation and the VSS is now telling the ECM INCORRECT data. The 4L60E shift, shift firmness , and torque converter lock-up are all decided by these factors.

96capricemgr in response to your statement of;

"If the pcm were reprogrammed just to fix the speedo but not the shift point then that would be right but we are talking stock programming. So again how does the pcm know the change occurred?"

The shift tables go off of MPH and throttle percentage on a table, as stated above, if youre expecting the 2-3 shift to occur at 25 mph at say 20 percent throttle , then if the VSS is giving incorrect information in relation to the number of tire revolutions per minute, then the shift will be delayed til a higher RPM is reached.
The shifts are not by RPM but by MPH.
As we know with a 3.23 gear the engine will turn less rpms to reach a given mph than with a 3.73 rear gear.
In Tunercats when you adjust the speedo it automatically does the math and changes your shift tables to reflect the new mph that it should do its shifts at.

 

how does the pcm know the vehicle speed has changed in relation to VSS output?

 

It doesnt it is dumb as far as that is concerned and only has the VSS signal to tell it whats going on out back. It plugs the number of pulses from the VSS into an equation (the other part is th gear ratio and tire size) and then determines what speed the car is going, if the math equation is off the speed is off that it beleives the car is going, when in reality it is going a different speed.

I just realized I danced around what you were asking, The PCM only knows the other part of the math equation by input from the programing, the second part of the math equation that it puts the VSS number of pulses with, is made up of the tire size (you input tire size and it determines by that the outer diameter of the tire and how many turns it takes to go a distance) and the gear ratio of the diff.

 

You'll be fine, it will give you like 200 more rpm to play with but if your on the stock tune and it don't hit rev its actually going to help you.....I went from 3.23 to 3.90 and it made it rev around 450rpm higher but it was still in its power range and knocked .2 tenths off my 1/4, my tune identify stock tho and I'm nowhere around my rev limiter, so just toss it I. and try it....and you can snag a used hypertech off this forum for 100 bucks all day long.......good luck!