LQ4 + TH400/350 setting up P/N switch to help idle trims

[wfo9]

Question for those that have done LS swaps with old school autos behind them.

I have an LQ4 in a rock buggy. Having a few idle issues and I feel some are related to the fact that I have no Park/Neutral switch and with the low stall and extremely low gearing it gets a little confused at times with idle trims and how much airflow is needed when in and out of gear. I feel having a Park/Neutral signal to the PCM would help a bunch to have access to the different Base RAF tables....

ECU is a 2002 P01 out of a Silverado 2500

So I've researched but can't find an answer if this will work or not.. I have found bits and pieces of info. My rough plan is as follows:


- Go to transmission configuration and go from
General TransType:Non-elec Auto PRNDL Equipped:None
to
General TransType:Non-elec Auto PRNDL Equipped:PN Only

Then take PINs 32 and 34 of the blue connector of the PCM and tie them together and ground them whenever the transmission shift selector is in either Park or Neutral position. I Plan to do this with a Dakota Digital universal Gear Shift sender and a relay which would route 32 and 34 to ground.

When I look up the pin outs in various places is says 32-PRND A input and 34-PRND B input. I also read an old post somewhere that this wiring would work to signal Park/N to the PCM.


I'm asking here because I would like to at least hear this approach should work before attempting it just to be frustrated with the results...


Related question, does anyone know what triggers idle routines vs decel when no speed sensor is hooked up.

[5FDP]

I honestly did nothing when we put a Th350 behind a 5.3 in rock crawler.

Left the transmission as a 4L60e, disabled all abuse modes and transmission related DTC's. As well as anything else that wasn't there anymore and it runs and drives great, has no trouble idling and returning to idle.

[blindsquirrel]

This diagram is from the Description & Operation section of the manual, easier to make sense of what happens when than the one in the regular trans schematics section.

screenshot.16-05-2021 21.18.49.png

P: 32+34
R: 32+72
N: 34+72
D: 62+72
3: 32+34+62+72
2: 32+62
1: 34+62

[wfo9]

This diagram is from the Description & Operation section of the manual, easier to make sense of what happens when than the one in the regular trans schematics section.

screenshot.16-05-2021 21.18.49.png

P: 32+34
R: 32+72
N: 34+72
D: 62+72
3: 32+34+62+72
2: 32+62
1: 34+62

Good info. I could use that approach and have it emulate N and D with a relay.. I could setup the trans position sender to Ground 32+34 whenever N or P is activated, and ground 62+72 whenever in R, 1, 2, 3..

I think the gear reports as 14 or something in P... Once I'm able to flash the ECU I'll test it out manually messing with the wires.

[wfo9]

I honestly did nothing when we put a Th350 behind a 5.3 in rock crawler.

Left the transmission as a 4L60e, disabled all abuse modes and transmission related DTC's. As well as anything else that wasn't there anymore and it runs and drives great, has no trouble idling and returning to idle.

It runs now.. just has some awkward idle behavior at times. A big part of it is probably the tune itself, which I have been unable to work on so far due to a licensing glitch that I can hopefully get HPT to resolve next week.. It has a cam so the idle has a pretty good chop to it.. I wish it had a stock cam in it, but the power is kinda fun as well. It's sort of a mix between a crawler and a rock bouncer. More crawler for sure, but I'm not really up for taking it apart and putting stock cam back in it at the moment. It may eventually come to that down the road if I end up wanting to tame it down more.

[Fast4.7]

Flip the switch from 4L80 or 4L60 to non computer controlled automatic and re-write all. Zero out all the torque management for the transmission. Worked on my buddies 6.0L/TH400 in his 98. No speedo since it was to make it to a race event after he smoked his 80E after the converter grenaded.