Why is my 4L80E shifting weaker?

TacomaJD · Feb 10, 2014

My truck (2006 GMC 2500HD 6.0L gasser with 4L80E tranny) has started shifting noticeably weaker over the past couple weeks, enough to get my attention. I have been running the Diablosport Predator tuner on the 87 Octane tune and increased shift pressure just a fuzz when installing the tune. It's been probably a year or so since I put the tune in it and it has done flawlessly ever since up until lately. It used to shift firmly when hitting 2nd and 3rd, especially more firmly when accelerating harder. Now it just sort of slides smoothly into those gears. Checked tranny fluid and it is still a good color of red and is not low.

Figured I'd post and see if any others have had any experience with this. It doesn't slip by any means, but it is definitely not shifting like it used to. Have not had battery off or anything like that, that may affect retaining the tune or whatever. No idea what's going on, but I get the feeling it's maybe an electronic issue, not a mechanical issue, but I can't be certain. Any input before I hook the programmer back up to it and try to reflash the tune or tweak the shift pressure parameter?

Bumpers · Feb 10, 2014

Re: Re: Why is my 4L80E shifting weaker?

Unhook the neg cable on the battery for a few minutes then hook it back up see if it changes.. the computers learn with conditions and adjust parameters to current conditions .. if you have bedn grandpawing the truck around it may have backed off the shifts a fuzz.. worth a shot

You don't have to worry the tune won't be goin anywhere

TacomaJD · Feb 10, 2014

Re: Re: Re: Re: Why is my 4L80E shifting weaker?

Bumpers said:
Unhook the neg cable on the battery for a few minutes then hook it back up see if it changes.. the computers learn with conditions and adjust parameters to current conditions .. if you have bedn grandpawing the truck around it may have backed off the shifts a fuzz.. worth a shot

You don't have to worry the tune won't be goin anywhere

I kinda thought that may have been how it worked, but wasn't certain. I haven't pulled anything in a few months since my rig has been down so it has been paw-paw'd more lately than usual. Makes sense, I'll try the ground cable thing and see what happens. Thanks!

TacomaJD · Feb 23, 2014

Re:

Well....went to town earlier with a buddy in my truck on a drunk run to get some late night Krystals and before making it back home, truck randomly went into limp mode twice. Wtf?

Haven't taken battery cable loose yet and have not hooked programmer up to truck to see what code it's throwing since engine light is on. First issue I've had out of this truck in the 25k miles I've put on it. It's almost right on 120k miles. Gonna try to check it with the programmer tomorrow after work some time. Hope it's not related to the tranny and maybe something gay like an 02 sensor or something.

KILLERB468 · Feb 23, 2014

see if it has a low line pressure code since it went into limp mode.

muddinmetal · Feb 23, 2014

Re:

TacomaJD said:
Well....went to town earlier with a buddy in my truck on a drunk run to get some late night Krystals and before making it back home, truck randomly went into limp mode twice. Wtf?

Haven't taken battery cable loose yet and have not hooked programmer up to truck to see what code it's throwing since engine light is on. First issue I've had out of this truck in the 25k miles I've put on it. It's almost right on 120k miles. Gonna try to check it with the programmer tomorrow after work some time. Hope it's not related to the tranny and maybe something gay like an 02 sensor or something.

I would lean towards a throttle body issue.

TacomaJD · Feb 23, 2014

Re: Re: Re: Why is my 4L80E shifting weaker?

KILLERB468 said:
see if it has a low line pressure code since it went into limp mode.

What would this signify if that was the code? Will be this evening after work before I can hook it up and see.

TacomaJD · Feb 23, 2014

While having some down time at work, I've found a good thread on Pirate with a lot of info about this. Good read for any others' curiosity. Could be Throttle Body, Throttle Positioning Sensor, or wiring issue. Due to the fact that something fawked up in my truck that makes the driver's side blinkers not work, it wouldn't surprise me if it's some sort of wiring issue.

http://www.pirate4x4.com/forum/general-4x4-discussion/931651-6-0-litre-chevy-reduced-engine-power.html

Jep72m · Feb 23, 2014

Re:

Have you Checked your ignition switch yet?

Sent from my SAMSUNG-SGH-I337 using Tapatalk

zukimaster · Feb 23, 2014

The trans issue will be a pressure control module more than likley, they get weak after a few years, and cause a sluggish 1-2 shift, part is under a 100 bucks, and is easily replaced.

TacomaJD · Feb 24, 2014

Re: Re: Re:

Jep72m said:
Have you Checked your ignition switch yet?

Sent from my SAMSUNG-SGH-I337 using Tapatalk

What exactly would I check for in my ignition switch?

And didn't get a chance to check the code last night, ended up working late. Been busy as **** again today too and work tonight. Will try to check code tonight after work.

TacomaJD · Feb 24, 2014

Re: Re: Re: Why is my 4L80E shifting weaker?

zukimaster said:
The trans issue will be a pressure control module more than likley, they get weak after a few years, and cause a sluggish 1-2 shift, part is under a 100 bucks, and is easily replaced.

Hmm. Reckon that could get bad enough where it would make it go in limp mode?

First time it done it that night, I just pulled up to the gas station, cut it off, went in, came out, crunk it up and it was in limp mode.

2nd time it done it a couple minutes after cranking it again, pulled out of a buddy's driveway, stopped at red light, went to take off and it went into limp mode. Both times, just had to cut it off and let it sit for a minute or two, crank it, and it was fine and drove like normal.

onepieceatatime · Feb 24, 2014

Have you tried putting it into Tow/haul mode? I think 2500's have them. I know on my 1500 that changes some things in the transmission and could help you in troubleshooting. Are you running the tunes that came with your programmer? I bought mine through Diablewtune.com and you send him some data logs and he builds you a full custom tune and can change around a lot more stuff and it really opened my truck up even more.

KILLERB468 · Feb 24, 2014

Re:

muddinmetal said:
I would lean towards a throttle body issue.

was going to mention this as well after thinking about it more today.

Jep72m · Feb 24, 2014

Re:

Our company truck started acting similar to what you described. Then we noticed the tachometer started acting up then all gauges would act up. After taking it to the dealership multiple times it ended up being the ignition switch. Was told by a GM guy that the main power wire for the transmission runs through the ignition switch so when the ignition switch goes bad it makes the transmission do strange ****. Just a suggestion if you have time Google bad ignition switch and transmission problems in a Chevy truck and about 20 pages will come up. $80 switch fixed our issue and it runs fine now.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

TacomaJD · Feb 24, 2014

Re:

Jep72m said:
Our company truck started acting similar to what you described. Then we noticed the tachometer started acting up then all gauges would act up. After taking it to the dealership multiple times it ended up being the ignition switch. Was told by a GM guy that the main power wire for the transmission runs through the ignition switch so when the ignition switch goes bad it makes the transmission do strange ****. Just a suggestion if you have time Google bad ignition switch and transmission problems in a Chevy truck and about 20 pages will come up. $80 switch fixed our issue and it runs fine now.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

Awesome, will read into that also. Thanks a lot! :dblthumb:

TacomaJD · Feb 25, 2014

Re:

.....umm, plugged my Diablosport programmer in the OBD II port and nothing happened. It doesn't come on. Wtf?

Reckon it could be on a fuse along with something else that may have blown and causes it to act funny?