First issue with the 8HP70

[Kotta390]

Tonight while driving home I got off the highway, left the truck in 3rd gears going around the clover leaf and nailed it doing 39-40mph. With the 3.92s the truck "should" stay in 3rd and truck along. What actually happened blows my mind. While doing this the truck proceeded to what felt like a violent downshift and then throw the truck into limp mode... I had to come to a stop, shut the truck off so the trans would auto shift into park. Restart the truck and move along.

So before I did this, the EVIC told me to service the trans and had a check engine light on, but no messages in the EVIC?? So after restarting the truck, I babied it home and she drove just like normal, just with a CEL on the whole time. I stopped by and got something quick to eat and after I came back and started the truck the CEL wasn't on anymore. It's been shut off for only ~10-12mins? She still drives fine. Went ahead and went for broke and did two back to back 40mph take offs in 3rd gear and everything worked as advertised.


Wtf just happened?? Lol I'm clueless and usually if you have a CEL then it pops up in the message center but I got nothing? Should I take the truck into the dealership and see if they can find a pending code related to the trans? Or should I leave it alone and chock it up as a "hiccup" in the system?

 

[sicmadek]

Tonight while driving home I got off the highway, left the truck in 3rd gears going around the clover leaf and nailed it doing 39-40mph. With the 3.92s the truck "should" stay in 3rd and truck along. What actually happened blows my mind. While doing this the truck proceeded to what felt like a violent downshift and then throw the truck into limp mode... I had to come to a stop, shut the truck off so the trans would auto shift into park. Restart the truck and move along.

So before I did this, the EVIC told me to service the trans and had a check engine light on, but no messages in the EVIC?? So after restarting the truck, I babied it home and she drove just like normal, just with a CEL on the whole time. I stopped by and got something quick to eat and after I came back and started the truck the CEL wasn't on anymore. It's been shut off for only ~10-12mins? She still drives fine. Went ahead and went for broke and did two back to back 40mph take offs in 3rd gear and everything worked as advertised.


Wtf just happened?? Lol I'm clueless and usually if you have a CEL then it pops up in the message center but I got nothing? Should I take the truck into the dealership and see if they can find a pending code related to the trans? Or should I leave it alone and chock it up as a "hiccup" in the system?

Its actually more common than you think. The pcm thinks the engine speed is too fast.

 

[Kotta390]

Its actually more common than you think. The pcm thinks the engine speed is too fast.

Oh wow... So did I hurt the trans at all or do I need to have it checked out?

 

[shane1981]

mine has done it twice and the tuner says engine over speed .I just clear it and keep going it doesn't hurt anything but I wouldn't do it all the time it eventually could

 

[Kotta390]

mine has done it twice and the tuner says engine over speed .I just clear it and keep going it doesn't hurt anything but I wouldn't do it all the time it eventually could

It's the first time it's done it to me and I've had it almost new and truck has 25k on it. I was wondering if the TCM was looking for different values because I swapped gears.

 

[bassheadhemi]

It's the first time it's done it to me and I've had it almost new and truck has 25k on it. I was wondering if the TCM was looking for different values because I swapped gears.

That would make sense

Did you unhook the battery since you did the swap? maybe there's a auto learning process involved that will take care of it

 

[shane1981]

mine has 3000 miles on it 8 speed 3.92's from the factory . the rev limiter is proly set too close to the shift point but I'm not sure . disconnecting the battery will proly clear the light but the computer will still store it but I don't know how long. I also have the pcm and runner for mine and it still does it . I'd rather it do that than come apart.

 

[Kotta390]

No and I may have my buddy at Chrysler reset the TCM adaptives to make sure.


To answer your question Shane, the code will stay dormant or "pending" until the allotted amount of drive cycles have been done to confirm the issue isn't present anymore.

 

[Wild one]

Made a hell'va squeal didn't it,lol.

 

[Kotta390]

Made a hell'va squeal didn't it,lol.

No it was more like a jerk then anything.

 

[H8Speed]

Anybody with an 8 speed and 3.92's wound theirs out?Curious what top speed is limited to with that gear.

 

[THETANK]

I would bet 105-106

 

[H8Speed]

I would highly doubt that lol I have 3.55's and can do damn near 150.

 

[Zeak]

I had my Outdoorsman reading 115 when I let off. I was passing a truck and when it passed 100 I stayed on it to see when the computer would shut it off. It got to 115 and I am not sure if that was when it was shutting down or if it was slowly gaining more. I figured it would have been limited to 105 or something.

 

[sicmadek]

He is referring to a tuned truck

 

[Zeak]

That may be but if my stock 8spd with 3.92 will hit 115 then that is faster than a previous belief of 105-106. I was just answering his question with my experience. I too am curious what the top speed may be but I don't think I will have mine over 100 again.

 

[H8Speed]

I am irresponsible and stupid sometimes on empty highways,was just debating on 3.92's since I lost a little bit of low end with cam swap,was just curious how much it would effect top end.

 

[Zeak]

It would still be fast enough to get you into a lot of trouble and or killed. Acceleration is more fun than extreme top end so I say if your working on making it quick you may as well do gears.

 

[Thepopeofpoland]

My 2013 with 3.92s hits 115 before it's limited and will not accelerate anymore.

 

[Thepopeofpoland]

My stock 2013 with 8speed and 3.92s hits 115 then holds and won't go faster. Found this out racing my buddy from 70 mph rolling start.