LMM: Does anyone else's truck

[TwoTone]

shift down to 5th constantly going up hills at medium to high elevation? My truck is on its 5th EFI tune now by two guys. Im at 5000ft and often up to 7300+. When I'm at lower elevations my truck stays in 6th but around here when my cruise is on I often get so annoyed with the constant shifting from 6th to 5th and back that I lock it into 5th. And with each tune when its climbing a steep grade in 5th it surges. Also sometimes when I gun it it hesitates to shift into the next gear but it doesn't over rev. The current tune that is on my truck has it running the best so far, actually around town its a beast. When trying to fix the constant shifting my previous tuner put a tune with more pressure into my Allison. Other than 4" cat back my truck is completely stock. I have had the suggestion of getting a EGR blocker though my tune has it shut off. Any help would be great. I love my truck but I'm sick of the shifting

 

[JoshH]

A tune with more pressure in the Allison?

Is the constant shifting happening loaded or empty?

 

[TwoTone]

Both. Actually when I was pulling a cattle trailer unloaded into 50mph wind a few weeks back the son of a bitch was in 5th and shifted down to 4th on steep/long grades

Yea I'm pretty sure it was a tune with more pressure to the Allison

 

[The Neens]

I'm surprised you haven't got a DTC by shutting the EGR off with stock exhaust...I had trouble with 2 trucks years ago by doing that...I retuned it with leaving the EGR system stock and the issues and DTCs went away...

 

[TwoTone]

I don't have stock exhaust... Just the cat

 

[The Neens]

I don't have stock exhaust... Just the cat

So you have a cat and no DPF?

This is where filling out a signature comes in handy

 

[08txlmm]

have had the suggestion of getting a EGR blocker though my tune has it shut off.

If you don't have a blocker plate leave the EGR turned on. I had the same problems when I had a quadzilla without a blocker plate. Then I installed a plate and got EFILive. Still had the same problems until I turned the EGR back on. Not sure why that is but after a full flash and letting the trans relearn a bit the problem went away.

 

[messejme]

I have heard that the EGR valve can be forced open due to pressure when it is not commanded to open?

 

[LWATSON]

Yes, you can force the EGR open, I think around 25 psi. blows it open if you dont have a blocker in.

 

[JoshH]

I have never had a problem shutting off the EGR without having a blocker plate. Been doing it on my dad's truck for over 100k miles. I also did it on my truck for about 40k miles before I bought one of Rick's EGR delete pipes. I wouldn't do it with a DPF still in place though. I don't believe that has anything to do with the downshifting.

There really isn't much I can do without seeing the tune, and since you are running someone else's tuning, I don't really care to see it. I would suggest looking over all the medium and high altitude tables to make sure you are allowing full fueling at higher altitudes. You may also try bumping up the boost pressures in the mid range of the medium and high altitude tables.

One more thing, I don't know what pressure supposedly was increased, but the main line pressure in the Allison is controlled by valves and springs. The only way to increase it is to go into the transmission. The only pressures you can change are the TAP cell presets, and those things start to change as soon as you put the transmission in gear.

 

[Mike L.]

Josh is correct. You can only raise pressure at the PR spring in the stator support.(pump)

 

[Mike_S]

My suggestion, find a tuner that isnt going to feed you lines of bull. You cannot control line pressure to any point of usefullness with EFI Live.

 

[08txlmm]

I know you know a lot more about tuning than I do Josh but I had the exact same problems as described above and it was due to EGR surging. I could actually hear and feel the EGR valve open at higher boost levels before I had a plate. I still had the same problems with a plate and EFILive with the EGR tables off while my brother with the same truck setup wasn't having any problems so it may come down to more of a truck to truck issue. I turned the EGR on and had the tables stock and it stopped downshifting.

TwoTone I researched this for weeks when I was having the same problems and everything I found pointed to something in the ECM tuning and to leave the TCM alone. I would suggest returning the TCM to stock and atleast try turning the EGR back on, it may not work for you but it's an easy fix to try.

 

[LWATSON]

The op mentioned his tuner put more pressure in his trans. Do you think maybe he ment he adjusted it so it takes more throttle input pressure to make it downshift? My tuner did the opposite on my tune. It downshifts with less throttle input to help spool my charger.

 

[Mpsoldier]

i have the same thing with my lmm constant down shift from 6th to 5th gets annoying

 

[RoboF16]

Sounds like normal shifting to me considering the higher elevation, up a grade, etc. Bigger than stock tires would make it worse. 6th is pretty tall gearing in these trucks. Don’t know if you have an EGT gauge but your engine will be more efficient closer to the torque peak and will run cooler at a given load. Many think they will hurt fuel mileage by running a lower gear but that’s not necessarily the case.

 

[TwoTone]

The op mentioned his tuner put more pressure in his trans. Do you think maybe he ment he adjusted it so it takes more throttle input pressure to make it downshift? My tuner did the opposite on my tune. It downshifts with less throttle input to help spool my charger.

I just talked to him and he just adjusted the shift points up is what he said.
The first couple tunes I ran were from DuramaxTuner's library of tunes. The one I have now is one the guy I just had retune it made. I like it in general a lot more.

Sounds like normal shifting to me considering the higher elevation, up a grade, etc. Bigger than stock tires would make it worse. 6th is pretty tall gearing in these trucks. Don’t know if you have an EGT gauge but your engine will be more efficient closer to the torque peak and will run cooler at a given load. Many think they will hurt fuel mileage by running a lower gear but that’s not necessarily the case.

Even so it would not explain why every tune I run in 5th surges

 

[bluessmax]

I have come across this issue a time or two due to egr...datalog it and vane position...that will truly tell you what the deal is. Has your tuner requested a datalog?

 

[08txlmm]

The first couple tunes I ran were from DuramaxTuner's library of tunes.

Here's your first problem. I ran his tunes my first set because I got a great package deal on EFILive, gauges, etc. Switch to a better tuner and you will be very happy with the results. I went with IdahoRob (after I ran Duramaxtuners tunes for several months) and I was very happy with the new tunes even if I did have to pay again. It's well worth the cost to get tunes from a better tuner.

 

[RoboF16]

Even so it would not explain why every tune I run in 5th surges

True. Rob told me and others have posted that many LMM trucks surge when you delete/disable EGR w/ EFI Live. The alternative is to modify the limits such that it never meets the parameters to turn on.