Issue with shifting after dyno tune

[Z06Luke]

Last week I dyno tuned a customer's 2003 Silverado 2500HD with 6.0. The truck was stock and the owner was mainly looking for better fuel economy, but was happy to get more power as well. I made the following tuning:

- Removed speed governor
- Increased spark advance in the partial throttle area of the 2200-2800 RPM columns until the dyno no longer showed torque gains
- Increased spark advance in the WOT areas of the map from 3200 RPM on up

There was an unusual issue that we had where high speed flashing would fail, so I pulled a few of the common fuses to no avail (the stereo was factory, fwiw). I decided to proceed with the slow method of flashing. One of these times when attempting to flash the computer bricked, so I disassembled it and grounded the reset PIN and was able to write-entire and get it working again. Upon the next write attempt, the computer bricked again and could not be recovered by using the reset PIN, so I took another P59 off of the shelf and installed it in his truck and did another write-entire. The truck worked great and the tune was complete. We drove the truck on the street and the owner was very happy.

He hooked up his travel trailer and went on a trip and reported to me when he returned that when he had the trailer hooked up that the truck would not go into overdrive even when tow/haul mode was disabled, and upshifts were extremely hard! He says when driving it with no load that it runs just as good as it did when we test drove it after the dyno.

I have not yet ridden in it while pulling a trailer, but I am very confused about this since I did not make any changes to the shifting any other transmission settings. I have attached both the original unaltered tune (AsFound), as well as the final tune (V2). If anyone has any ideas that might help identify what's happening here I'm all ears.

AsFound.hpt V2.hpt

[Alvin]

The upshift extremely hard part makes me think there is a code in it.


The flashing issue is common with that year range. Pulling the radio amp and radio fuse seems to help. Sometimes only low speed.. Sometimes they won't read back out too.

[Z06Luke]

Yeah I pulled both of those fuses to no avail. What do you mean by having a "code" in it? Like a DTC?

[TheMechanic]

Yeah I pulled both of those fuses to no avail. What do you mean by having a "code" in it? Like a DTC?

Yes. He means is there a "P" code in the PCM typically either a TPS related code or a P07xx code.
When they have issues it will default to high pressure and harsh shifting as a protective measure

[04silverado6.0]

I do know some os will default to max psi when in SD mode. That is probably new enough that it dont. Also I've never had a 03 year that didnt fail the write on occasion. I've had 1 that didnt require a bench at some point.

[Z06Luke]

I got to see the issue first hand today, and it was throwing the following codes:

P0741 - Torque Converter Clutch Circuit Performance or Stuck Off
P0894 - Transmission Component Slipping

It never failed to shift into OD while I was present with the truck, however I definitely saw the slippage. I wrote the tune to another spare P59 I had on hand and installed it in the truck and that eliminated the issue. I labeled the ECU and I will probably use that in the future on a manual transmission vehicle.

Thanks for the help all, I definitely learned a lot with this one.

[TheMechanic]

I got to see the issue first hand today, and it was throwing the following codes:

P0741 - Torque Converter Clutch Circuit Performance or Stuck Off
P0894 - Transmission Component Slipping

It never failed to shift into OD while I was present with the truck, however I definitely saw the slippage. I wrote the tune to another spare P59 I had on hand and installed it in the truck and that eliminated the issue. I labeled the ECU and I will probably use that in the future on a manual transmission vehicle.

Thanks for the help all, I definitely learned a lot with this one.

As a suggestion. If you have an ECM/PCM that is known to be a failed part I would never install it in anything. Even though the internal component is only part of the auto trans control that doesn't mean it won't create other issues. You would be using it at your own peril. Considering the cost of a new/rebuilt P01/P59 etc. that one would go in the trash.

[HATEHPTUNERS]

and next time you have TCC/Torque converter issues or issues with converter clutch performance, there are several things you can log to see if the problem is MECHANICAL, or electrical/tune related. Log TCC slip RPM, and TCC enable... Then go out and drive it.. When the PCM commands lock up-just watch the TCC SLIP rpm.. Under steady throttle at say 55-60, in 4th gear, when the converter locks the TCC slip RPM should be -10 to a positive 10 or so... Any slip RPM that is higher than 100 or so, and you have mechanical issues with either a worn valve body bore, worn tcc valve in the valve body, or the clutch inside the converter is now burned. Customers that try and tow trailers, without pressing the tow haul button, are very prone to smoke the single clutch in the torque converter... That clutch cannot handle the added weight of the trailer, and that is why the tow/haul button disables tcc lock up... but some customers just want to get the best fuel economy, at the peril of destroying their lock up clutch inside the converter. Also, on high, or higher, mileage 4L80E's the torque converter lock up issues are very common... In fact that is the #1 reason that 4L80E's come through my shop after they are 220K + miles... failed, or failing, lock up and associated TCC codes and issues. If you swapping the computer REALLY fixed his problem.... That's a new one on me.. I can count on 1 hand the # of bad GM PCM's I have ever come across. That # is very small. But it can happen.