411 PCM, trans tuning, compression braking, closed throttle tuning help.

[BRAAPZ]

Want to incorporate some engine braking on drop throttle down hills, nothing crazy just some amount.
Short version; Only at ?closed? throttle does the PCM not shift the trans as programmed, any throttle position greater than closed and the transmission follows exactly as programmed.
Is there a setting in the PCM that overrides the commanded gear shift when the throttle is closed/zero effectively ignoring the shift points as programmed? (Same behavior when trans is in ?TOW/HAUL? mode, at closed throttle it does not follow what is commanded).

The details; Adjusted trans shifting properties to not allow 4th gear below 49mph on upshifts and down shift out of 4th whenever drops back below 45 MPH, these adjustments took effect and function flawlessly, EXCEPT at closed throttle, 0% throttle, regardless of vehicle speed. Trans wont make the shift automatically though while logging during testing the scanner ?says? it is doing just as I programmed yet the transmission is not actually shifting down, though if I manually shift the shift lever from D down into 3rd it then actually shifts into third, (manually shifting at closed throttle works, programmed shifting at closed throttle does not). This anomaly only happens at closed throttle, all other throttle positions the trans behaves as programmed. Scan shows this as well, note at above 60MPH when the throttle is dropped, (0% throttle), the ?Selected Gear? shows a shift down from 4th into 3rd, though the trans is actually still in 4th, (note the RPM didn?t rise to correspond with ?selected gear? when it changed. A little later I manually shift the lever from D down into 3rd and the trans does shift down shift into 3rd, note the rise in RPM and the corresponding increase rate of declaration).
In short while logging with the scanner the ?Selected Gear? reflects all up shifts and down shifts as I programmed whether I am shifting it manually with the shift lever or just letting it shift automatic, the ONLY exception is at ?closed? throttle, the down shift is called out but does not actually take place unless I manually shift the shift lever, it ?indicates? what I programmed and intended it would do yet the trans is not physically making that shift unless I manually shift from D into 3rd. (repeating myself now, part of getting older... )

What am I missing here? A setting that overrides the commanded gear shift when the throttle is closed?

Paul

[5FDP]

I do not believe those computer incorporated a grade shifting type feature into the calibration, so it won't actually switch down to 3rd gear while coasting.

I think it's because of the style of transmission and the parts it uses. It has overrun clutches that work when in D4 and allow the engine to freewheel and not use engine braking. The shift selector has to be in D3 to allow engine braking.

[kingtal0n]

I get perfect engine braking in 4th with a 4l80e, what trans is this? Are you using a locked converter?

[BRAAPZ]

I do not believe those computer incorporated a grade shifting type feature into the calibration, so it won't actually switch down to 3rd gear while coasting.

I think it's because of the style of transmission and the parts it uses. It has overrun clutches that work when in D4 and allow the engine to freewheel and not use engine braking. The shift selector has to be in D3 to allow engine braking.

Hmmmmm.... Is there a work around to fool the trans alone into thinking that the throttle isn't closed when it actually is so it will avoid the "Coasting" protocols and actually shift down as commanded just as it does now when the throttle is cracked? I realize we want to retain the PCM's ability to recognize closed throttle, (zero % TPS) as so many other facets of the engine tune rely on that so I think actually resetting TPS to indicate anything above 0% when closed, (if it could be done), is not an option. But if the trans alone can be fooled in not seeing closed throttle then possibly it should follow the programmed gear changes (as it does now when the throttle is just cracked and more), allowing some form of rudimentary grade shifting function? ... or am I off my rocker on this one?

I get perfect engine braking in 4th with a 4l80e, what trans is this? Are you using a locked converter?

'01 Burb 1500 4wd, 5.3 LM7, 4L60E. Yes the converters is remaining locked, (light blue line in the scanner pic). Mine will engine brake great, but only if I manually down shift.

[BRAAPZ]

Little more research reveals that mechanical internal workings of the 4L60E, (and others), are different for PCM requested gear selection vs shift lever gear selection in regards to how and when "what" solenoids-clutches are engaged to achieve coasting or overrun in which gear at what time etc. Auto Trans design and function is not one my strong suits so for now I put the trans tune at 0% TPS to match that of 6%. Looks like to acheive engine braking with my 01 4L60E without having to manually shift is quite a bit more involved requiring a shift kit/custom built trans. That might be an option if/when this trans starts to die.

[ChrisM510]

I know this thread is a little old now, but has anyone figured out a solution or workaround for this issue? I never had this same issue when stock, so I am convinced it has to be something PCM related. I am a *complete* noob to HPT, but am trying to learn. Any help/advice would be greatly appreciated!

[BRAAPZ]

UPDATE!
Short version, ordered a custom built 4L60E WITH Engine Braking built-in, (only effective in the lower gears, not 4th), trans is en-route now from PerformaBuilt to be delivered in 3 days. Now I would like to learn more about shift tuning to take as much advantage of this built in engine-braking as possible, any input, links to more in-depth shift tuning studies, etc, will be greatly appreciated.
Was told by the builder that shift points and Torque Converter tuning is fair game but please leave the shift pressures stock, even at the custom Level 3 build with Engine Braking mod added.

Longer version, rig is now at 270,000 miles, collapsing lifters were giving fits, trans is slow to shift on occasion, and always that concern in the back of my mind the Transfer case could be wearing through any time now.... Couple months back I removed the LM7 and installed a fresh stock rebuilt LQ9, (to receive the BTR Torque cam soon), enjoying the added the torque the LQ9 brings to the drive, will be doing some more towing of our 7000 lb travel trailer back and forth over the Cascades Mountains here in Oregon this year, its time I get things rolling, make sure this rig is ready for what is coming. Talked Ryan at PerformaBuilt transmissions and after some back and forth we settled on the Level 3 Extreme 4x4 Max with engine braking added and a new Boss Hogg HD Torque converter.

[Oldchevy4x4]

Hey out of curiosity what gear ratio and tire size are you running? I assume 3:73 and 285/75r16s? What did your rpm map look like?

[BRAAPZ]

Hey out of curiosity what gear ratio and tire size are you running? I assume 3:73 and 285/75r16s? What did your rpm map look like?

Final drive for now is 3.73:1, (planning to go 4.10 in near future), Tires are 275 70/17" BFG KO2. After fine tuning tire size widget, in 3rd gear with Torque Converter locked, 2000RPM=52mph, 2500rpm=64mph, 3000rpm=76/77mph.Have not mapped out 4th or the 1st or 2nd.

Hope that helps,
Paul