5.3 swap, 4l80e won't engage
 

Hoping to get some help troubleshooting my swap. I have a 5.3 mated an early (91ish) 4l80e. Trans was rebuilt with hd2 kit. It has a short shaft I think with no NSS. Trans and trans diag is flashed to the PCM correctly and PRNDL is set to none. Harness is reworked as per lt1swap. Trans has at least 12 qts in it.

I got the swap running and driving seemingly fine a few days ago. Shifted ok and drove fine on the freeway. Didn't overheat. However now when I put it in drive or reverse it doesnt engage. If I leave it in gear for a very long time it will start moving eventually and will run up through the gears. But once you stop again it has the same issue. It always seems like if I wait long enough it will catch and start moving.

When I initially had this problem I checked the codes - p0706 and p1810. P0706 comes back consistently. I assume it is due to there being no NSS and needs disabled. P1810 has not come back but has me suspecting a bad pressure switch manifold (switch is new but who knows).

It has at least 12 quarts in it. I have the lokar firewall mount dipstick installed. Its reading close to full engine warmed up and idling. Ive tried playing with the fluid level and it may make a difference but not consistently. I didnt think to calibrate the dip stick when I installed it and now I'm regretting it.

Here are some ideas I had for what to do next
- suspecting bad pressure switch. Drop pan to check dip stick calibration and install a new switch.
- suspecting nss wiring. Try a wiring PCM pin 34 to ground to act as a P/N switch. Maybe PCM can't tell I'm in gear and thinks I'm still in park?
- get a pressure gauge and test the transmission to verify pump is working right.
- pull trans (will have to pull engine too get it out, ugh) take it back to shop for examination sonce its under warranty.

Sorry for the long post. Can anyone help point me in a direction? I'm a bit lost at this point.

Have you tried Moving the shifter to D1 or D2 or D3 and driving it that way?
Have you done a simple pressure test?

It was the same behavior in all the gears.

Got a pressure gauge on it today. Zero pressure in park and all the gears. Tested it again a little while later when it randomly decided to engage right when i started it up. 30-60 psi in park reverse and drive but eventually fell to zero.

Sounds like the trans is bad and needs to come out? Anything I can look at while its still in the car?

Sounds like you're about 2.5 or 3 qts low on fluid
Not verifying was a bad idea


dumping 2 or 3 qts in is an easy way to check. If that fixes it...drop the pan and verify fill level.
If it doesn't fix it...yank the trans. Check the filter and pump.

Yep. Put 2 quarts in this morning. Pressure started at 60 psi but dropped to zero soon after. Sounds like I need to pull the trans.

Without constantly having a good range of line pressure...

It is time for an overhaul... Sorry. :thumbsdow