4L80E behind 6.5 Turbo Diesel, not downshifting out of OD when going up a hill

[454/4X4]

1995 K2500, runs great, shifts great....if I am running along at 55mpg, in OD...and I come to a hill, it starts to lose speed if I dont give it pedal obviously...as you would expect. But...I pretty much have to floor it to make it kick down out of OD to let the engine rev/make boost if im towing anything or if its a decent incline. Normally, Im pretty sure that, if pedal is applied and speed is not gained, it should automatically downshift or at least unlock the TC...which seems to be the key...the TC isnt unlocking under a load....


Any ideas?

 

[tanman_2006]

Sounds like a trait of cheap econ tuning. Check for codes, underlying codes cause alot of issues sometimes. Codes dont always trigger CEL/SES

 

[great white]

Yup, the tc is factory coded to disengage with application of throttle, with "zero" throttle and with application of the brake pedal.

Is it that the tc is not unlocking or that the transmission is not shifting?

If you want to see if it will unlock, next time tap the brakes. If it doesn't unlock there's something wrong. You don't have to actually apply the brakes, just make the brake light switch. That's what the PCM watches. You'll only see about a 200 rpm just with tc disengagement.

They don't always automatically unlock or downshift in response to loss of speed. Its dependant on conditions. I'll try and have a look through a stock calibration file and see what's up. Can't remember off the top of my head...

Try it in cruise control. That sucker will definitely drop it down a gear if it looses speed on a hill. Any speed. If even cruise won't kick the revs to the stratosphere, there's a problem somewhere.

 

[great white]

This should help you to know what it should and should not be doing:

You must be registered for see images attach

That's from an OBDII F code calibration, but they should be close enough for gov't work.

 

[tanman_2006]

GW the video is inactive/deleted

My econ tune sticks in OD for awhile but it will down shift with alot of pedal.

 

[great white]

GW the video is inactive/deleted

My econ tune sticks in OD for awhile but it will down shift with alot of pedal.

Not a video, it's an image.

I can see it fine on my end....

 

[rhino]

The TPS sensor controls when it downshifts. I would have it checked. They go out a lot.

 

[great white]

The TPS sensor controls when it downshifts. I would have it checked. They go out a lot.

Well, yes and no.

% thottle is one of the things that does determine shift points.

However, the 6.5 doesn't have a traditional TPS. It is a "fly by wire" throttle. The APP (Accelerator Pedal Position sensor) is a part of the throttle pedal itself:

You must be registered for see images attach

It's triple redundant. Meaning; there are 3 "TPS" signals from it to the PCM. It's set up this way because a throttle fail could mean a runaway in a diesel, especially an electronically controlled one like the 94+ 6.5's.

It is also very rare for them to fail or fail completely. It does happen, but rare. There would be a "Service Throttle" light on in the cluster if even 1 signal fails. 2 signal fails will set the truck into a "limp mode" and limit the amount of throttle available. 20 Mph seems to ring a bell, but don't quote me on that.

Right idea, wrong truck.

 

[454/4X4]

Econo tune sounds likely, in the 2 months Ive had it, Ive found it lacks power...like as soon as it makes boos,t it defuels.

Ive got a gauge on it now, and with 31" tires, if I punch it off the line, it revs some, and makes boost, in fact..nearly 12psi of boost (nearly), and launches hard...but it will not spin the tires, and I get no black smoke.

It runs like a top, one of the best running 6.5's Ive ever seen, and will likely never have a better one...its just slick. But towing, it makes power, builds boost, but will not kick out of OD or TCC lockup unless I near about floor it. And as soon as I lift at all, it locks back in...

How do I get rid of a possible Econo tune on a 95 model?

 

[great white]

Econo tune sounds likely, in the 2 months Ive had it, Ive found it lacks power...like as soon as it makes boos,t it defuels.

Ive got a gauge on it now, and with 31" tires, if I punch it off the line, it revs some, and makes boost, in fact..nearly 12psi of boost (nearly), and launches hard...but it will not spin the tires, and I get no black smoke.

It runs like a top, one of the best running 6.5's Ive ever seen, and will likely never have a better one...its just slick. But towing, it makes power, builds boost, but will not kick out of OD or TCC lockup unless I near about floor it. And as soon as I lift at all, it locks back in...

How do I get rid of a possible Econo tune on a 95 model?

They are talking aftermarket calibrations.

You need a new chip in the pcm if that is whats going on, but I doubt it. If it's not colder than a witches t......errr, really cold, where you are you can pull the glove box out, pull the PCM out ad then look under the plate. The chip should have big printed letters on a tag like BXPY or something similar. If there's none, you may possibly have an aftermarket chip in it.

Gm only has a standard set of calibrations for these old hacks. There is no "econ" mode or performance. Anything like that is aftermarket.

If it's hitting 12 psi then it is supposed to defuel so that's no surprise.

Does it still have the vacuum system or is it running a wastegate spring?

My 6.5 dyno's 250+hp and 450+ lbft and it doesn't smoke anymore than a puff on start up. I tune my own (I'm one of the few that can do OBDII 6.5's and even fewer can do them right) and it's about as hot as you can get a 6.5 without getting in to major problems.

A properly set up 6.5 doesn't smoke.

An improperly set up one or one with problems smokes.....