2004 GMC 8.1 idles perfect won't go

[Smilie427]

2004 GMC 2500HD with 8100 Vortec Allison 5 speed
Predator U7193x
Updated to version v.9r11 May 4 , 2012

I first removed the 3 fuses as per the instructions . Installed the 87 tune with no mods to any parameters . Started truck and it had surgy idle . Tried driving the truck and it just falls on its face off idle . No codes , nothing . Won't rev fast in low gear , will sort of accellerate in 2nd but if you let off the gas won't go again . Reinstall stock tune runs normal . Had to go back
to work so wait a week to try again . First try at 87 tune removed 3 fuses again plus disconnect brake controller . Same as first time won't accelerate but no choppy idle . Also once it starts accelerating it keeps accelerating even when you let your foot off the gas . Reinstall stock tune back to normal
tried 87 tune again but correct for tire size and turn off torque management.
Same deal won't rev til 2nd then intermittent normal accel . In low gear will rev slow til redline shift .
Reinstall stock tune again and it's normal .
Saved the first tune with no mods and the original tune .
Is this a common problem with the 8.1 ?
If I can't load a tune what do I do with the Predator ?

[mikel]

we'll get you a new tune asap...

[Smilie427]

So no luck on getting this to work ?
Is there a product available that will work with the 8.1 ?
What do I do with the predator that I can't return to the store ?

[mikel]

sorry, we should have it for you today.

[johan]

New one here for you

[Smilie427]

So I had time today to try the new tune . Still idles perfect still won't go . The truck wont accelerate past 1500 rpms under load so it won't shift into 2nd . If it shifts into 2nd it will accel ok but if it downshifts no go . I just drove around the block as if it won't accel in low I didn't want to be in traffic . Came home and tried the Diablo tune instead of the 87 or the custom 87 and it's the same . No accel in low gear so I came back and installed the stock tune and it's back to normal .
What now ?

[johan]

I think i see what the issue might be here, please try this one and let us know.

[Smilie427]

Hello . I tried the new tune today . Well now it won't idle correctly . I fired the truck up and the idle hunts from 300-1500/2000 rpms and back . Then it seemed to stabilize at 500 rpms . Backed out of the driveway and go forward and ....nothing . No throttle just 300-500 rpm idle speed . Backed back into driveway OK , throttle in reverse . Sitting in driveway in P,N or D no throttle input . Reinstalled stock tune and normal again .

[mikel]

are you 100% sure you are loading the tunes properly/
selecting the stock tune when DSDL asks you to show it the 'base file'?

[Smilie427]

Yes . I have been installing the Diablo 87 tune to the truck then coming inside to download the saved original tune to the computer . Then I upload the new custom 87 tune to the Predator and installing that on the truck . The only difference I see is the original saved files are 330 kb vs 262 kb for the tunes I'm downloading from you .

[Smilie427]

No ideas ?
Is there any way to see if the truck has already been tuned and that is what the problem is ?

[70Camaro406]

Sounds similar to my problem I've been having for over a year now with my '04 Suburban 2500 with the 8.1. With the 87 tune installed, when first started, it would idle smooth for 5 seconds, then idle rough for 4-5 seconds, then smooth, then rough, etc. And when I tried to rev it up, it would get "stuck" around 1800-2000 rpms, like there was a rev limiter there. It would require more throttle to rev past that point. And as for driving, mine would do the same thing but only sporatically. Sometimes, 1st gear would be fine and 2nd gear would lose power.
The guys are great here, and tried helping me a bunch, but even they admitted that the 8.1 is a hard engine to tune. There are some owners that swear that their 8.1's run awesome...they must have gotten lucky somehow. Good luck.

[06MonteSS]

yeah.... things can be made better with a custom tune done for it....