Limp Moded Tranny?

[Shawn T]

I am still at a total loss. I have heard once your tranny goes into limp mode it becomes a lot more sensative to torque surges. A couple of years ago, it limped out. I was on the 3rd stage (never have had it on 4 or 5) of my Diablo Predator. It has been on stage 1 since (just a custom speedo program). If I accelerate with 1/2 throttle or more, especially WOT, it falls flat on it's face until I let off of the throttle. Other than that the truck has run flawless. It's still under the 7 year/100,000 mi power train warranty. I took it to the dealer and they diagnosed a #8 injector low flow. Change it, didn't work. Then it was a fuel pressure regulator. Changed it, nothing. They started throwing parts at it like crazy until I just gave up. My questions are:

 

Can the tranny "limp" without throwing DTC codes?

Is it even the tranny?

Is it dumping fuel, boost?

 

WTF? I have been to hell and back trying to figure this out! The stock motor output should not limp the tranny right? There is no real affect under normal circumstances but when I jump on it to pass or even tow a trailer up hill, it just quits. Please help. No codes btw, only an occasional 0401 low egr flow at times when I run at high altitudes. I removed the cat and added a 5 inch Dynamax from the cat back. No new down pipe.

[00Silverado4x4]

Possible failing fuel pump? I'm not real sure about the limp mode systems of these trucks.

[Carder09]

There was a thread about this before, I.want to.say it only takes 3 times in limp mode to permanently damage the Allison. Hopefully some one will chime in.

[Shawn T]

I'm hoping somebody will chime in too. I've posted this topic before and have never got a definitive answer. It doesn't feel mechanical. The tranny only limped once.

[yukon25008.1]

I also heard once it does go into limp mode..its downhill from there.. 'chevyboy86' Has a suncoast allison and says that it is bullet

proof and good for like 600 hp and 1200 ft lbs! not that you have to get that crazy but you may want to look at the suncoast website,

[Silverado4x4]

I would remove the tuner and put it back to stock tune, could be the tuner.

[gmtech4]

allisons dont limp,that term is BS,the allison will default and do something that gets your attn when a code is tripped and turns on the MIL ,if there is a code in the TCM it will also throw a 700 dtc in the ECM telling you to go to the TCM and pull a code

 

falling on its face is the engine ,not the allison transmission,the programing in that TCM is awesome IMHO,

 

i was a tranny guy for 3 yrs...trust me

 

if its alittle cold out (not sure of temps ) it will start off in 2nd or 3rd to warm up ,,,if its stupid cold out ,it will say "bite me ,its to cold and you will have to wait a few minites" lol

[8.1HD/ALLISON]

+1 I would remove the diablo. clear all codes and drive it for a while to see what happens. Could be somthing with the programming.

[Shawn T]

Rob,

That sounds correct. More like the motor "quiting" or dumping. Ran a test this morning.

Warmed it up to open thermo temp

Ran it down the rode with tuner still on stage 1 towing as previously mentioned.

Bit the dust on every hard acceleration and a stopped WOT it just crept along until I let off.

Removed custom tune and backed up stock tune to TCM

Does not fall on it's face so hard but, there is still something wrong. It just struggles to pick up speed and shifts erratically. Definatly not as bad with the stock tune. From a stand still, it wouldn't even break the tires loose. I have changed the filter recently and when the dealership was bombing it with parts that was the first one they hit it with. There is not doubt in my mind it's not a fuel filter. Allthough, the symptoms are similar. I checked for DTC codes also. None. I'm still as lost as ever. As I mentioned before it does have a modified exhaust, which I hardly doubt would have any ill effects. I'm sure you are right, so we can probably rule out the transmission at this point. Also, forgot to mention, the tranny temp was about 100.

[Shawn T]

It's fixed. Something so simple, I feel like a horses patute! I consider myself intelligent and halfway mechanically inclined, but man am I dumb as heck sometimes. I'll never put it past myself to skip the obvious and go straight for the complicated. I'm so sorry for wasting everyone's time. I have been having my services done by a friend here at a local shop for the last 2 years. She knows how thorough I am and knows that you NEVER trust the air filter indicator! It reads 100% filter life. I pulled it. Suffice to say, a rat has been living in my intake for about 2 years. Among the giant tufts of hair I found about a roll of wadded up TP and 30+ cigarrette filters. You can literally see about 40% of the actual filter inlet side. I removed it, and it shifts and runs like I just drove it off the showroom floor. I then installed a custom tune of 50 HP for fuel economy and towing along with a speedo tune. It runs and shifts even better. I'm going to head to the parts store for the filter and start inspecting my own filters from now on. I would even be humble enough to post if picture if anyone is so morbidly curious. Halleluyah, holy s$*t!!! Where's the tylenol!!?

[Carder09]

Wow......

[txab]

[8.1HD/ALLISON]

Sh!t happens... At least it was an easy fix. Happens to the best of them.

[yukon25008.1]

When i was younger i would go on a 'no heat' service call..I would always do that, look for major issues or problems.. And 8 out of 10

times It was a loose low voltage wire, switch at the top of the stairs off, etc...

So now i take my time..Step back and really think ans look at the whole picture!

[Shaners]

Hmm... probably should check mine. It is the original and I know have had critters chew up the insulation on my firewall!