How to wire up a NP 236 in place of a 136.

[tanvanmanwithaplan]

I can help with with connecting to the ECM, if you need it, but not sure what year you have.

I drilled a small hole in the firewall behind the battery…3/32 bit, I think.
Then,I shrinked wrapped the section of line that runs through the engine bay with 1/8” wrap, and sent the shrink wrap through the hole in the firewall to make an airtight seal.
Then, I ran 1/4” loom over that back to the firwall.

You have to remove the battery, but then you have a chance to clean and paint your batttery tray.

I have a 2001. I need to source an ECM pin. I have the two connectors so I think I need pin 16 on connector 2 according to prior comments.

Anywhere to source pins online? are they easy to crimp? For most of this project I have been reusing donor pins with the wire attached and inline soldering them to primary auto wire with marine grade adhesive 3:1 double wall shrinkwrap.

[AstroSurf]

I cut the ECM plugs off an Astro at the junkyard, so I have a ton of pins attached to a few inches of wire. (Still in plug)

I can harvest a few pins and mail them to you, if you want, or a whole plug, so you can see how it comes apart before you you start.

They’re plugs from a 2003-2005, though. Not sure if they would be the same pins or not.

[tanvanmanwithaplan]

I cut the ECM plugs off an Astro at the junkyard, so I have a ton of pins attached to a few inches of wire. (Still in plug)

I can harvest a few pins and mail them to you, if you want, or a whole plug, so you can see how it comes apart before you you start.

They’re plugs from a 2003-2005, though. Not sure if they would be the same pins or not.

I appreciate the offer but don't go thru the trouble since we're not sure if it's the right pin or not. I think I will call local GM partshouse on monday to figure out interchange and get a part number for the pin and which vehicles it in then I can go to JY to get one or just order some online. I'll be sure to post my findings here for future people.

I will say though looking back this conversion is probably 3 times as much work as I imagine the 233 manual linkage is because you have to do almost all of that work. The kicker for me is this electronic one doesn't take up additional floor space for that linkage shifter. If I have clutch problems down the line I may switch to electronic shifting 233 or maybe a 243/233 hybrid (no idea if this is even possible lol)???

[tanvanmanwithaplan]

Called GM and did some research. For my van (2001), as indicated in this thread it uses the red and blue plugs. You can buy these on ebay if you search for LS SWAP PCM. I am going to try to source one locally and if not, buy a whole plug set from eBay rather than drive to the pick n pull ( 2 hours each way for me ).

Interchange is roughly all 2001-2002 4.3 L35, 5.7/350 vortec, 4.8L, 5.3L, 6.0L, 8.1L, LS from what I can tell.

I ordered this plug https://www.ebay.com/itm/313027673040 $20 is steep for one pin but I don't really have time to get to a pick-n-pull and the local salvage yard sneered at me for asking about an engine harness.

[AstroSurf]

Looks to be the exact same as as the 03-05 plug, but the change in color from red to green.

Sucks...I could saved you $20, if I knew.

[tanvanmanwithaplan]

Pin is run, 4low works, although I'm not sure it didn't work the whole time as after hooking the pin up it still didn't go into 4lo...

Then I tried neutral on the transmission and it clunks in. Is it normal for it to not want to go into 4lo when in park? It will go between 2hi and 4hi in any condition.

[tanvanmanwithaplan]

Looks to be the exact same as as the 03-05 plug, but the change in color from red to green.

Sucks...I could saved you $20, if I knew.

It's OK since I only removed one pin I can just resell it on ebay so it doesn't go to waste.

[Herbie]

Pin is run, 4low works, although I'm not sure it didn't work the whole time as after hooking the pin up it still didn't go into 4lo...

Then I tried neutral on the transmission and it clunks in. Is it normal for it to not want to go into 4lo when in park? It will go between 2hi and 4hi in any condition.

***The pin isn't to tell the TCU to go into 4lo***, the pin lets the TCU tell the ECU that it IS in 4lo so that the ECU doesn't freak out at the disparity between input and output shaft RPMs and limit the transmission to 1st and 2nd gear. Without the pin connected, you can't get past 2nd gear in 4low.



Regarding shifting while in park, not sure about the 236-based trucks, but on the 233-equipped trucks (S10, etc.), the procedure calls for Neutral:

Shifting from 2HI or 4HI to 4LO
To shift from 2HI or 4HI to 4LO, the vehicle must be
stopped or moving less than 3 mph (4.8 km/h) with the
transmission in NEUTRAL (N) in vehicles equipped
with an automatic transmission or the clutch pedal
engaged in vehicles equipped with a manual
transmission. The preferred method for shifting into
4LO is to have your vehicle moving 1 to 2 mph (1.6 to
3.2 km/h). Press and release the 4LO switch. You must
wait for the 4LO indicator light to stop flashing and
remain illuminated before shifting your transmission
into gear or releasing the clutch pedal.
If the 4LO switch is pressed when your vehicle is in
gear and/or moving, the 4LO indicator light will flash
for 30 seconds and not complete the shift unless your
vehicle is moving slower than 3 mph (4.8 km/h) and the
transmission is in NEUTRAL (N) or the clutch
pedal engaged.

This next bit might help you out also:

On automatic transmission equipped vehicles, if your
transfer case does not shift into 4LO, your transmission
indicator switch may require adjustment. With your
transmission in NEUTRAL (N), press and release the
4LO switch. While the 4LO indicator light is flashing,
shift your transmission into PARK (P). Wait until the
4LO indicator light remains illuminated before shifting
your transmission into gear. This will get you into 4LO,
but you should take your vehicle in for service to restore
normal operation

[Astrophysics]

Hi Herbie,

Good info on 4LO, TCU wire to get all 4 gears of the automatic tranny when in LO range.
I did that mod with a micro switch on the manual shift linkage with my np231 C manual
T case.

2. Later this week I should be getting my 2003 AStro 4x4 back with 4.10 gears and rear Eaton tru tac.
I am excited to get the new gear ratio to have better performance with the 30 “ tires.

AP

PS
I have been exploring ideas to make stronger front bumper with spacing of Wrangler JK bumper.

[Herbie]

Yeah, a microswitch is the common solution for np231 (or converted np233). You'll love the 4.10 gears! Best mod I've done to mine so far.

Can't wait to see the bumper.

[tanvanmanwithaplan]

I tested 4lo the other day in a friend's yard where it's always soggy. I sloshed the rear axle to where it spun, put it in neutral, then 4lo. It pulled out without any complaint or loss of traction. 2Hi has been great driving around pavement with the front driveshaft in an no worries. I am scarred because I blew up my NP136 with these bigger tires after changing a flat tire and I guess I was a little lazy with the rotating. Don't have to worry about that anymore as AWD will only be on in icy/snowy conditions.

My $200 parts puller transfer case with fresh fluid isn't making any noise and I've done two 5 hour trips in it. Pro tip: Get your transfer case from a salvager not a pick n pull. Pick n pull wants $140 for a xfer case WITH core and I got this one with KNOWN MILEAGE (78k) for $200. In no universe is $60 worth the hassle of pulling the blazer xfer case. Pulling the xfer case on the Astro is a breeze but the blazer is ridiculously tight.

[tanvanmanwithaplan]

I put a Detroit TruTrac in the rear end and it immediately blew up the transfer case FYI. It's clacking and grabbing like the 136 used to do already.

Also, I have it up the ground right now doing diagnostics on it and noticed that my ECU pin wiring doesn't seem to be working. When the transfer case is in 4 lo it will not shift into 3rd.

[MountainManJoe]

Interesting. Any theories why the TC blew up?

How useful is 3rd when you're wheeling around in 4-low? At that speed, doesn't it make more sense to be in 4-high in 1st or 2nd?

[Herbie]

Interesting. Any theories why the TC blew up?

How useful is 3rd when you're wheeling around in 4-low? At that speed, doesn't it make more sense to be in 4-high in 1st or 2nd?

Not strictly needed, but it's convenient not to have to keep switching back and forth if you get to a smooth section - especially if you've got a manual-converted NP233 like me. There are some FS roads I do frequently where it makes it a no-brainer to just leave it in 4Low. I also find being able to run 1-4 in 4Low seems to keep the transmission running a little cooler than having to hold 1-2 in 4Hi.

[tanvanmanwithaplan]

Interesting. Any theories why the TC blew up?

I rotated in a full size spare recently, this is also what made my 136 start grabbing and making noise years ago. The first time (6 years ago) I installed a brand new spare into general grabbler AT2 30x9.5 tires that had probably 10-15k miles on them after breaking a belt in one of the rears. This time, I preemptively rotated my full size spare in at 2500 miles (new tires again) to try to avoid this from happening again, this time general grabber ATx 235/75r15. No problems until trutrack install and new pinion bearing & seal and carrier bearings. I put calipers on the tires, the difference between tread depth is 1/2mm. Probably unrelated but I also recently (last week) completely replaced ALL the brakes.

It does not make any noise in 4hi, just in 2hi. I dare not even test AWD, LOL.. I did not put the blazer axle disconnect on the van. I believe that would prevent this from happening. Think of it, if the front axle disconnect wasn't needed why would they have gone to the trouble of engineering it? It doesn't help with gas mileage...

I am still diagnosing to verify my initial thoughts. I just took the front driveshaft off and I am going to go test it now to be certain it isn't something other than the transfer case.

How useful is 3rd when you're wheeling around in 4-low? At that speed, doesn't it make more sense to be in 4-high in 1st or 2nd?

Even with the NP236 you need to be in neutral to get into 4lo, so shifting past 3rd would be really useful. It is a secondary concern to the transfer case exploding itself within 3000 miles though. OP, did you do the front axle disconnect?