oharajo

Hi all,

I've mostly swapped a freshly built 4L80e (with 2500 stall) into my '08 Silverado 1500 4WD. It now goes drives forward in all gears: Park, Reverse, Neutral, D!

If I rev to around 2000 rpm in park, neutral or reverse it rolls forward, but it goes forward more easily in D and D2. I haven't been brave enough to go very far on the road to see what it does at higher speeds.

I've tried unplugging the transmission connector to eliminate wiring because I've read that the tranny should still drive forward and backward without the connection (in limp mode I think?), but the tranny still behaves the same and goes forwards. This makes me think it is something mechanical in the tranny.

When I shift into reverse, my reverse lights come on, the truck realizes it is in reverse, just not the transmission.

I'm throwing codes P0700, P0973, P0976 and P2764.

Anyone have suggestions as to what my could be or what I should check?

On a similar sounding post (https://ls1tech.com/forums/automatic...e-neutral.html), I've seen Jake suggest "Could be the manual valve not connected to the linkage." I'm guessing I would drop the pan and hopefully I can check if the linkage stud on the outside of the tranny is connected to something?

Any help would be much appreciated!

PS: my programming and wiring
I think my programming/wiring is good, though given that I still have a problem without the transmission connector plugged in makes me think the problem isn't electronic. For programming, I bit the bullet and licensed an '08 Express w/4.8L and 4L80e and did a write entire, then wrote my old ECM tune back over it, but killed the Hp Tuners program before it could overwrite my TCM. I believe this left me with my old ECM tune and a 4L80e tune on the TCM. I rewired the harness including wiring up the VSS and ISS (including the pin 45 to 26 change at the TCM connector for the ISS low signal).

Jake's Performance

iTrader: (2)

It's not a wiring issue. It is internal. Most likely the manual valve.

oharajo

I pulled the pan, and I think the manual valve was hooked up properly. I've attached a pic, does this look good? When I shifted the linkage manually the manual valve also seemed to shift.

If I'm right that the manual valve is good, any suggestions as to what else might it be?

Also possibly relevant is that when I initially installed the tranny, I had the front VSS plugged into the ISS sensor slot, no ISS plug, and I was a couple quarts low.

With these mistakes, it still reversed pretty well when I rev'd it to 2500 rpm (which I figured might be because I had a 2500 stall). It would also creep very slowly forward in when I rev'd it really high (like 3500 rpm, and then only barely). Would this have been limp mode?

After I corrected all these mistakes, I got my current problem of it only wanting to go forward in reverse, neutral and drive. Any help would be very welcome!

Thanks!

Way Deway

Did you ever figure out the problem? I have the same issue with mine all gears go forward even park tries to take off. Any help would be greatly appreciated. Thanks

Blackice720

I'd unplug the transmission main connector just to rule out anything electrical. If you run it without the connector plugged basically the trans will run in limp mode with line pressure maxed out. See if reverse works with the main harness unplugged.

Also (since you have the pan off) I'd verify the roller detent is bottomed out in the rooster comb in each gear. Your shifter linkage may need adjustment. You could be shifted in reverse on your shifter, but not be fully engaged in reverse in the trans.