manual gear selection overide 4l80e

[2500ak]

Hypothetical question:

2001 LQ4 4L80e GMC

Tables / Values (D0913, D0918, D0928, D0914, D0919, D0933) are manipulated thusly:

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(These apply when the column shifter is in manual low position)


[D0913] Manual Hold Gear 1st 1->2

Maximum speed before the PCM will force an upshift to 2nd if the gear lever is being held in 1st

Set to out of range

[D0918] Manual Hold Gear, 1st, 2->3

Maximum speed before the PCM will force an upshift to 3rd if the gear lever is being held in 1st

Set to out of range

[D0928] Manual Downshift 1st 2->1

When slower than this speed the vehicle can be put into 1st manually

Set to maximum safe speed relative to rpm

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(These apply when the shifter is in manual 2nd)

[D0914] Manual Hold Gear 2nd 1->2
Generally the original values are 0 up until WOT Meaning that it starts out in 2nd and stays there until WOT

Set all values to 0

[D0919] Maximum speed that the PCM will stay in 2nd while the shifter is in 2nd before forcing the 2-> 3 shift

Set to out of range

[D0933] Manual Downshift Gear 3->2 Shift
Allows a downshift from any higher gear to 2nd with the column shifter

Set to maximum safe speed relative to rpm


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The reasoning behind this is at some point I plan on adding a ratchet shifter, getting this correct will render a little more control. Also I don't like the idea of the mechanical and hydraulic components of the transmission at odds with the tuning. zeroing out the [D0914] would just be too allow a 1->2 upshift at any given throttle position.

Has anyone ever tried this manipulation?

The reason I ask is because on the more electrical transmissions the manual valve controls the pressure manifold switch more than anything else.

Although I have gearcommand (Transgo HD2's clever little plug in the actuator feed passage at the end of the manual valve bore) the pesky 1-2 shift sometimes still occurs at part throttle.

Are these values what command that part throttle shift that sometimes occurs?

I am considering either taking up tuning or just getting my truck tuned and I'd like an opinion on whether or not what I have just suggested is wise.

Any input is appreciated.

[joecar]

What are D0961, D0962 set to...?

What vehicle...?

[2500ak]

This is all hypothetical so I am not at all sure what the kickdown values are. All I presently have to work with the the demo version, the truck is a 2001 2500HD Sierra, with the 6.0L and 4L80e.

The only thing I'm sure of in this case is that the values for kickdown would be stock.

I think I see what you're saying though. If the trans holds first to rev limiter under full throttle, but does not always hold first under part throttle, the throttle position is relevant?

In any case if the adjustments I suggested were made, would this cause complications? Whether it works or not I figure its worth a try when I have the trucks custom tune made, as long as there isn't any possibility of it messing with other aspects of the tuning.

Times like this make me wish I wasn't such a broke college student so that I could order the software now, and tune it myself.

[joecar]

Those settings should be ok...

(by "out of range" I know you mean "maximum allowable value", i.e. 256 mph).


These ones always work:
[D0928] Manual Downshift 2->1 Shift Speed
[D0933] Manual Downshift 3->2 Shift Speed

These work on the 0411 PCM running the common F/Y-car calibrations (4L60E):
[D0913] Manual Hold Gear, 1st, 1->2 Shift Speed
[D0914] Manual Hold Gear, 2nd, 1->2 Shift Speeds
[D0918] Manual Hold Gear, 1st, 2->3 Shift Speed
[D0919] Manual Hold Gear, 2nd, 2->3 Shift Speed

Those last 4 may not necessarily work on all PCMs/calibrations, but they are easy to test.

[2500ak]

Yes precisely, a speed higher than I could ever hope to reach.


I believe the NBS trucks, at least the ones from 01-02 use the 0411.

So when I have my truck custom tuned I will have these values modified.

My fear was that either the tuner would say that it wouldn't work, and that would be embarrassing; or even worse I'd have it shipped all the way up to Alaska and it would have some problem that would need to be sent back for readjustment. Which would also be very lame.

Thanks again for the information.