"Limp mode" hesitation on an 8.1 BB

70Camaro406 · Post by **70Camaro406** » Wed Jun 29, 2011 6:14 pm

06MonteSS wrote:all these sporatic, inconsistent issues, degrading after a while, makes me think something's up with the truck/tranny itself... like in one of your first posts, how you said it would act a certain way, a few times a day - sometimes it was ok, other times it wasn't... that's not really a tune issue - the tune doesn't change at all... once it's in, it's in...

does this seem to happen after the truck has been run a while, after it has heated up??? sounds like it runs ok for a while at first, and then after you've been driving a while, then it starts to deteriorate...

With the Hypertech (was on it from summer of '05 til early June '11), it ran fine...no driving issues at all. With the original Diablosport 87 octane tune with TM disabled (early Jun '11), it ran like a scalded dog. I only had issues with that one because it would sometimes go into a limp mode, which required me to mash the gas to get it to come out...that and the cold start rough idle, which would clear up as it warmed up. These two issues is what prompted this thread.

The custom tunes had horrible drivability issues... surging, extreme limp mode that even full throttle input had no affect, part-time throttle input - as in sometimes it would accelerate and sometimes nothing - even when it was to the floor. That's when I decided to put the 87 tune back in.

The only thing I didn't do with the custom tunes was to modify the parameters, as in disabling the TM and firming up the shifts. But that shouldn't affect the tune anyway. Or would it?

The one guy that posted earlier, bbyukonxl, has pretty much the exact same vehicle as me, except his is an '03 and mine's an '04. Something worked right on his though.

Post by **mikel** » Wed Jun 29, 2011 6:25 pm

I'll ask johan to look at that fix and see what was different about yours.

70Camaro406 · Post by **70Camaro406** » Wed Jun 29, 2011 8:00 pm

Thanks Mike.

bbyukonxl · Post by **bbyukonxl** » Thu Jun 30, 2011 5:45 pm

Sorry to hear about your issues but these guys will work it out!! I have never had any of your issues but then again each truck is different. Only probs I had was some bad 93 oct. Gas and exhaust leak that I fixed with some short tube headers.lew then dialed me in and it hauls ass now!

70Camaro406 · Post by **70Camaro406** » Fri Jul 01, 2011 8:05 am

bbyukonxl wrote:Sorry to hear about your issues but these guys will work it out!! I have never had any of your issues but then again each truck is different. Only probs I had was some bad 93 oct. Gas and exhaust leak that I fixed with some short tube headers.lew then dialed me in and it hauls ass now!

Thanks. I have faith that they'll get it straightened out. I'm going to upgrade the exhaust too, just not right away. I am, however, going to pick up a set of Edelbrock headerss for it. Summit has a screaming deal on them right now. My plan is to put on the headers and short lead pipes that comes with them, keep the stock pipes, 3" each, and cats to the muffler, replace the muffler with a Dynomax Ultra-X-Flow muffler, dual 3" in and dual 3" out like the factory muffler, and then replace the single 3" tail pipe with a single 3 1/2" pipe off of a diesel truck, which I already have. I'll do those mods the same time that I get a cold air kit, maybe K&N's kit or Volant.

I'm still amazed how much difference the 87 tune with TM disable and shifts firmed up made over the Hypertech tune. I mean, a couple weeks ago, I pulled out on this one road and layed into it and it barked the tires shifting to 2nd (Cooper STT 285/70-17's)...granted, it rained earlier that morning, but the roads were already dry and those tires really grip. I about fellow out of the chair when it did that.

Right now, though, I'm fighting it trying to replace a heater core. What a nightmare! Going on the second day.

Post by **mikel** » Fri Jul 01, 2011 8:40 am

try this.
load the 87 tune, and if it does the throttle limp, plug the tool in without shutting the truck off to see what codes are present.

cmg916 · Post by **cmg916** » Sun Aug 14, 2011 5:10 pm

[quote="70Camaro406"]Alright, got it in and went for a ride around the block. It's better, but I guess it still needs to learn some...doesn't go into limp mode, but hesitates a little as it speeds up. Should I drive it like this a couple of days and see how it develops? I appreciate all you guys are doing for me.

Attached is what I just installed.

Thanks,
Wayne

I have very similar problem. Starts after tuned (tried all 3) goes great in reverse haha, but falls on face when in drive almost like its stuck in ODrive and a 180 on a dist. Thanks

70Camaro406 · Post by **70Camaro406** » Thu Aug 25, 2011 1:27 pm

Yeah, mine still does it once in a while. I have Mike looking into it for me. I'm going to run a datalog next time I drive it, hoping to catch whatever is making it do that on the log.

smokestack · Post by **smokestack** » Thu Aug 25, 2011 4:53 pm

After reading this thread and looking at your profile pic. I would say weigh your wheels and tires. Just one and add 3

I have had issues working on trucks like yours with the allison. Seems that tranny wants to be dialed in. So you might have to do a dyno tune so they can watch the tranny. I would say the surging is the converter locking and unlocking. Once you mess with the TM its going to throw the tranny off even worse than the larger tires. Not sure about the CMR software but you should be able to calculate the rolling mass and tune that into the tranny.

Remember. This is just a guess. As i am not a tuner.

smokestack · Post by **smokestack** » Thu Aug 25, 2011 5:10 pm

Before the tuners here go nuts on it....as what looks like what happend

http://www.allisontransmission.com/

Check out that link. There are and has been a ton of recalls for that tranny. Everything from reflashes to new springs....clutchpacks and so on so forth.

Im not sure if the tuner touches the TCM or even if your truck has one. But i do know there was a update for it at the dealerships. And it solved alot of issues they had.I would imagine if the smart guys here could not solve your tune issues. Its tranny related.

Post by **mikel** » Thu Aug 25, 2011 5:46 pm

No, we dont touch the Allison TCM. I dont believe there are any handhelds that do...

70Camaro406 · Post by **70Camaro406** » Thu Aug 25, 2011 7:26 pm

smokestack wrote:I would imagine if the smart guys here could not solve your tune issues. Its tranny related.

It seems like all the 8.1 guys are getting this issue.

BTW, I have an 8.1 and a 4L80E....not an Allison.

70Camaro406 · Post by **70Camaro406** » Mon Oct 24, 2011 6:11 pm

I finally got a log of it acting up, but I only had my tuner with me and no laptop, but I logged a short complete GM data-log, and saw some of the stuff it was doing. When it went into limp mode, this time in 3rd gear, I gave it some more throttle to accelerate, the timing went down to -5 degrees. The timing and short term fuel is what was on the screen, and I noticed the decrease in timing to -5 or so, and the fuel went to zero's. Hopefully, you can get what you need from the dashboard, since that was the only way I logged it.

Post by **mikel** » Tue Oct 25, 2011 9:34 am

please export the last tune written and post it with the log

70Camaro406 · Post by **70Camaro406** » Tue Oct 25, 2011 3:48 pm

Thanks for the quick response Mike. I added the last tune written that I just got off of the tool.

"Limp mode" hesitation on an 8.1 BB

04 GMC 8.1L/Allison 5-speed automatic

RE: 04 GMC 8.1L/Allison 5-speed automatic