Harsh/firm shifts only after highway driving, especially the 1-2.

[AdsoYo]

I want to address an annoying problem I've had with this car since buying it. After driving on the highway, even for a short distance, once I'm back on city streets the 1-2 shift feels like max pressure. 2-3 and 3-4 feel noticeably more firm but not even close to 1-2. Same with shifting into P or R, noticeable more firm but nothing like 1-2. There are no DTC's on my hptuners scanner.

Once I turn the car off then back on, even if it's immediately, the problem is gone and it shifts normal again until I go back on the highway.

I first noticed it on the cross country drive getting the car home. We started in Philadelphia and first noticed it in Salt Lake City. It was infrequent at first and had gradually worsened to the point it does it after every highway drive.

I suspect it has to do with the torque converter locking, then when I'm back to city speeds it stays stuck in that "mode". Fluid is bright red and odorless.

After reading around the forums (and Gemini, don't hate), it sounds like replacing the EPC solenoid is a good place to start. Wondering if anyone has other thoughts/ ideas?

 

[mrrsm]

ATSG has produced an 87 Page Dedicated HP-Tuners Transmission Tuning PDF covering Tuning issues that may be related to the present shift problems as linked below. The Colorized PDF is too large to directly attach to this Post:

Resources - ATSG

* ATSG is a technical support service specifically for the Automatic Transmission Industry. We offer a Technical Hotline, Books, Software, Bulletins, Wiring Diagrams, Seminars, and Technical Courses to the Automatic Transmission Professional.

atsg.com

 

[AdsoYo]

ATSG has produced an 87 Page Dedicated HP-Tuners Transmission Tuning PDF covering Tuning issues that may be related to the present shift problems as linked below. The Colorized PDF is too large to directly attach to this Post:

View attachment 118814

Resources - ATSG

* ATSG is a technical support service specifically for the Automatic Transmission Industry. We offer a Technical Hotline, Books, Software, Bulletins, Wiring Diagrams, Seminars, and Technical Courses to the Automatic Transmission Professional.

atsg.com

View attachment 118815

Awesome! I'm at work but I'll check it out later. Although I don't think this particular case is tune related since it started while the car was bone stock and has gotten progressively worse. If it showed up after I started modifying then yes that'd be a major possibility.

 

[AdsoYo]

Went for a drive while logging on hptuners and found that the problem happens a second or two before the 3-4 shift at highway speeds. It won't happen at 40 mph. The TCM enters "diag max" mode and line pressure is pegged at 93 psi. Something is causing the TCM to enter "safe mode/ self preservation mode" just before that 3-4 shift. The EPC is functioning normally and the TCC solenoid seems to functioning normally. It's not showing any different numbers during the 3-4 than any other gear change.

This doesn't happen every time. I was driving for about an hour. When it went into diag max mode, I'd pull over and turn the car off then immediately back on and it would be cleared and shift normally again. This happened 3 times. Towards the end of the drive when I tried to get diag max to show it wouldn't.

I thought maybe there was too much slip but slip is usually between 150-200 rpm just before the shift and acceptable slip range in the tune is 150-1500 rpm.

Then I thought maybe the shift was taking too long but in the tune the shift time for 3-4 is zeroed out.

I noticed the P1811 and P0894 were both disabled in the tune which seems odd.

I wasn't able to find any channels for TCM or TCC adaptives but I should be able to make a custom channel based on what I found.

At this point the line pressure for the 3-4 shift is 640 kpa across the board and I want to try increasing it to 750 kpa just for s&g's. I'll also try disabling the TCC and take it on the highway. Problem is I have no clear reason for this. Only that it happens right before the 3-4 at highway speeds.

 

[AdsoYo]

On my drive today I used hptuners to lock the converter so it was locked during the 3-4, still happened. Then I flashed a new tune with the shift pressure increased from 640 kpa to 750, still happened. I logged input and output shaft rpm in case those sensors were erratic but the rpm's were equal.

I wonder if it's the 3-4 shift solenoid? Or the pressure switch manifold? I'll read around to see if it's possible to log that solenoid.

 

[Mooseman]

I want to address an annoying problem I've had with this car since buying it.

So you've owned this truck since new? Did it always do this? Is it possible a previous owner put in a shift kit?

Usually I tune my trannys to lock up the torque converter clutch to 100% instead of PWM modulation to reduce clutch wear and heat. Kinda feels like a 5th gear when it engages.

Have you also tried resetting the trans adapts?

 

[AdsoYo]

So you've owned this truck since new? Did it always do this? Is it possible a previous owner put in a shift kit?

Usually I tune my trannys to lock up the torque converter clutch to 100% instead of PWM modulation to reduce clutch wear and heat. Kinda feels like a 5th gear when it engages.

Have you also tried resetting the trans adapts?

No I bought it at 93,000 miles and drove it from Philadelphia to Oregon. It first did this in Salt Lake City during that drive. The previous owner bought it new in 2007 and kept it bone stock.

I haven't reset the adapts but I've had the battery unplugged for hours/days during the dod delete, supercharger install and other things.

I haven't tried turning off tcc pwm, although I did lock the converter manually so it was already locked during the 3-4 and it didn't make a difference.