TCC lock mod

[Bullseye240]

Does anyone know if the TCC wire runs to the ecm under the glove box and if so which pin is it so I can route my wires tomorrow while I have the headliner out for repair. A diagram or very clear instructions would also be helpful.
thanks in advance guys

 

[JiFaire]

I'm assuming this is for your 1994 Blazer? It only works on OBD-I trucks.

You need to supply ground to wire 'S' of the transmission in order to lock the PCM. You can either do this under the truck, or inside the dash, as follows:

Wire your switch into line C11 of the Blue 32-pin BC/BD PCM connector (see diagram)

I like to use 3position switches for this mod.

Switch Position

UP: TCC locked (manual) - Trans (wire S) is connected to ground, PCM (wire C11) is open

CENTER: TCC unlocked (manual) - Trans (wire S) is open, PCM (wire C11) is open

DOWN: TCC under PCM control (stock setting) Trans (wire S) is connected to PCM (wire C11).

Most of the time, I leave my truck in stock position... when it isn't loaded, the thing runs just fine, so I leave it alone.

When loaded (pulling 5er), I like to use the locked position from about 2nd gear on... but every once in a while, a big hill needs to unlock just abit to get over the top, and the Chip I have won't let that happen. I can either gently touch the brake with my left foot to unlock it (which must really freak out the guy behind me... the truck starts lugging, then the brakes come on and it speeds up ) or flip the switch. Touching the braks also requires that I slide the trailer brakes to zero so they don't grab... just flipping the seitch to manual unlock is the best option. Once I get over the top of the hill, I lock up again. I only do this when I need a little help in OD - if I let it slow down to 50 or so, it'll drop out of OD into third and the problem solves itself, anyway.

 

[Bullseye240]

Thanks, I don't do a lot of towing with my rig and I'm thinking this might help a lil with downhill compression braking and over all MPG on road trips. I post result and impressions when its done and has some miles on it.

 

[JiFaire]

You're welcome.

It is good for compression braking, but I don't think it'll help with your mileage out on the open road... the TCC mostly stays locked up anyway, at highway speed.

If you don't tow, you might rather have a simpler setup. A 2-position switch will let your TCC be controlled either by the PCM (leave line C11 hooked up to wire S) or by the switch (manually ground wire S from the tranny while leaving C11 open.

Don't ground wire C11... it will cause the PCM to notice and will give you a code. That wire either has to be open (connected to thin air) or hooked to wire S.

 

[Schwind]

I used a 2 position switch on my TCC lock up mod. Not just any switch will work though. It has to be a single pole double throw on-on switch. I only have the options of the PCM handling the TCC or manually locking it in. The mod still works great. I do have to say that the 2 position on-on switch was hard to find here, I actually had to order it from NAPA. I even had to look it up in the catalog myself because the clerk (counter guy I really can’t call him a parts man) didn’t believe that they made such a switch.

C11 pin location is the key. There are post on the other site that mention the wire tan and black or brown but on my 94 the color was wrong, my wire color was dark blue.

 

[Bullseye240]

Yeah already planned on useing the 2 position switch and will probably try this for the commute to work where the speeds are 45 mph so it should help a little there but I really can't complain about 16 mpg in city driving out of a fullsize suv with 234000 on it.
I will also be doing Turbine Docs FTB mod and prefilter FRB5 lift pump mods. I love the looks I get with my truck when I start it and a car parked 2 cars away has its alarm sound!!!