Can 4-3 downshift curve be at/below 2-3 upshift?

[Mach2]

OK another newbie question. Now that I have the trans shifting the way I want, I want it to hold 4th gear longer before downshifting, and go into 4th earlier to help on fuel economy. I already put values of 100% in the 4-3 throttle kickdown tables then took the Envoy for a drive and logged data. I confirmed it is shifting based on the part throttle upshift and downshift MPH tables.

I have already copied my Norm tables for 3-4 upshift and 4-3 downshift over to the cruise tables (I do not have tow/haul mode). Next I was going to shift all the cells down one so effectively downshifts would occur after 5-10% more TPS than stock, and upshift 5-10% TPS earlier. The question I have is can the 4-3 downshift table go below the 2-3 upshift table? Will this cause any issues?:Eyecrazy:

Attached is a file showing the stock 2-3 and 3-4 upshift/downshift schedules along with the proposed 3-4 modified schedule.

[ChipsByAl]

Can you put up a file with just the proposed shift points? Some areas are getting a little on the busy side. You don't want to get into fourth too soon and lug the engine. The cruise will probably be left best close to stock. The control will keep giving the vehicle throttle till the correct speed has been met. Going to the floor before it gets the gear and then an aggressive accelleration isn't the best for mileage.
Al

[Mach2]

Per request, here is the stock 2-3 up/downshift tables plotted with the proposed 3-4 up/downshift table. Note the 3-4 downshift table drops just below the 2-3 upshift table. Will this present a problem?

[joecar]

I think it may work, but if it doesn't then it doesn't... (...a very uncommital statement... ;) )

When it hits the 4-3 DS curve (going below it, from above), it will select 3rd even tho it is below the 2-3 US curve because it is still above the 3-2 DS curve...

4-3 DS curve is applied only if crossed downward and current gear was 4th.
2-3 US curve is applied only if crossed upward and current gear was 2nd.

so it will select 3rd, or so it seems to me.

[oztracktuning]

Just an extra idea.
Going into 4th early may hurt fuel economy the same as it staying in fourth too long. Increased engine load due to the lower torque in that gear will make it use more fuel not save fuel.

[joecar]

I agree, it will lug and it might not feel "right".

[Mach2]

Joecar: Thats how I thought it would work. Going to give it a try and see if it helps.

oztracktuning: I understand your comment, but believe it will not be lugging from this change. We have one of the few 5.3L Envoys made in 04 with the 3.73 gear. I have always felt it waited too long to shift into 4th and downshifted way too early going up hills. Since I have a trans temp gauge, I can always watch this, the coolant gauge, and the instant MPG monitor (in place of a vaccum gauge) to determine if the engine is lugging harder in 3rd or 4th.

Nothing ventured nothing gained (and hopefully nothing broken!):D

[ChipsByAl]

Mach2 have you given it a go yet? It looks as if it should work OK as long as the load doesn't increase too much.
Al

[Mach2]

OK, shifted all cells in the 4-3 downshift and 3-4 upshift tables down one cell and went on a 600 mile drive. Not towing saw no issues, in fact, it solved a problem I had with the vehicle not upshifting right away into 4th after cresting a hill. After 300 miles of towing it helped there too. It held 4th longer before downshifting, and MPG improved from 10.5 to 11.5. Now to taclke PE!

[Mach2]

A quick update: this modification to the downshift/upshift curves worked well! Last year when I towed my deck boat back and forth to the north woods I got 10.5-11 MPG depending on the weather. I had to tow in 3rd as the trans was constantly hunting between 3rd and 4th. This year i have made the same trip twice with the same boat and can now tow in 4th. My MPG is averaging 12-12.5 MPG! The only other change to the truck is the addition of a K&N cold air kit, which did add 15+ lb. ft. of torque. I am quite pleasedby a 15+% improvement in towing mileage.