How do you switch your PCM to the performance tables (for shifting)? Is it grounding a certain pin? I have a '95 trans am PCM.

 

You have to tap into some wires and add a switch. It's been so long since I've done it, I cant remember exactly which wires. So a search in Lt1 tech. For trans. performance switch, or button.

 

kevmor99 ... here is a url that should help you ...

http://members.***.net/chipsbyal/page/trans/

 

Thanks, so it's pin 13 on the C/grey plug. That page says you should ground it, with a momentary switch. I then looked at a pin diagram (http://csce.uark.edu/~jgbertr/rb/1995_pcm4.jpg) and it says it has B+ (http://csce.uark.edu/~jgbertr/rb/1995_pcm_conn_c.jpg) w/ key on and engine on? It seems like it should be ground as thats how the brake switch etc. work, but why does it say B+? I don't want to fry anthing

 

Hey kevmor, I'll be doing this same mod to my LT4 powered truck with 4LE60 this week end, It should be the C-13 pin directly to the PCM, the f-bodies have some other harnesses under the dash, such as the 230A, etc and the instrument cluster harnesses which you most likely do not have in your truck transplant.
I'm going to configure the "perform" tables for towing on my truck, lower line pressure, lock up TCC sooner in 3rd, etc.

You can use a cheap momentary switch from Radio Shack, they have several to choose from. The way the switch works is anytime after the engine is running, press the switch and the "perform" tables are used until either the switch is pressed again, or the engine is shut off, then it will reset back to "normal" mode.

 

It says B+ because that is the potential sitting on the pin at the pcm. If you noticed, the trans perform button is wired to ground on one side and the other side to that lead. When you press the button, the circuit is completed to ground. That causes current flow and the pcm toggles the mode from whatever the current mode is, to the alternate mode. Every time you press it, it will go from normal>performance or performance>normal. When the key is turned off, it reverts to normal on the next startup.

 

I'll be using my truck for towing also, how do you know what line pressures to use? Is a lower line pressure better for towing? I also haven't found anywhere that says how high is too high to make the pressure for performance shifting.

Do you think a more aggressive cam would hurt towing? I asked this before but nobody answered, not too many use their camaros etc. for towing I guess

Thanks shoebox, now I get it

 

ok, this is going to be long...
Luckily, my truck originally had the 4LE60 tranny and I had the hardware to pull the ECM chip and pull the tables off of it for the tranny. I was also able to pull the tables off of my wife's '95 TA, which also has the "perform" button on it and compare its "normal" settings with those that were originally in my truck.
This is a '94 Silverado ext. cab truck BTW.
The LT4 has been in about 3 weeks now, and has a 211/219 cam with a very short duration, so it idles very smooth, but produces 365rwhp/350ft-lbs at 4500 rpms.
With that said, and using the stock truck settings, the motor would wind well past 6k rpms before shifting with only about 3/4 throttle...way too loose for this powerful motor.
So I loaded all of the main line pressure and shift tables from my wife's TA into it...shifted much better and firmer...a little more tweaking on the TCC tables and the mph to shift table and now its great. The truck original MLP were almost half of that in the TA, I guess because the TA is lighter can could handle the thrust when it shifts where as the truck is heavier and would resist that "thrust" when it shifts and I'm sure its a little harder on the tranny but it feels the best...remember lighter line pressure will cause more TC slipage which also is bad and produces heat.
Main line pressures should not exceed 90-95. I guess the stock truck setting just did not have enough main line pressure to firm up the convertor fast enough for the torque the engine produced...thus letting it over rev each time before shifting.
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For towing, remember higher Main line pressure means hotter temps...also a non-locked convertor (slipping convertor) produces heat also...and heat is the biggest enemy to the 4LE60 and wear the clutches in the convertor faster. So, with that said, I plan to lower the main line pressures..by how much, I'm not sure. Also, will lock up the TCC in 3rd a little sooner, and hold 3rd gear longer before shifting to 4th..if I even use 4th gear while towing...if you do use 4th, be certain it is at a fast enough speed where the TCC can be locked in order to keep the heat down.
So anyway, the "perform" button will be rigged for towing.

It may take me several weeks to get it right for me to tow a 3k lb comp ski boat with my 3800lb truck.
I'd be happy to send you my PCM file to examine for the tranny settings...I still nedd to get my speed reading right to the PCM though, right now the PCM thinks I'm going 5 mph faster than actual at 35, and about 10 mph faster at 70, so if you want the file, keep that in mind when looking at any tables that use speed as one of the factors in it because it has been tuned like that by feel and watching the scan tool.

One other thing, the '95 4LE60 trannies use a pulse width modulated TCC solenoid, I guess to control how fast the lock up occurs, the '94 and below 4LE60's do not. I originally had a '95 PCM but it kept throwing a tranny code and then we found an extra wire going to the tranny that my truck did not have....reloaded the PCM with '94 f-body code and the code went away.

I have several versions of the PCM file if you want them:
1) LT1 with original TBI truck settings
2) LT1 with original '95 TA settings
3) LT1 with original '94 Camaro settings (same as '95 TA) but does not require the pw TCC solenoid that was throwing the tranny code.
4) My tweaked file that is currently in use..but no "tow" settings are in the "perform" tables yet.

All of the above have been tweaked for spark and fueling for my engine setup so they are not stock settings as far as the engine management part goes, only the tranny settings.

 

2QUIK6, thank you for all the info. Could you please email me the file w/ the truck line pressures? My email is kevmor99@yahoo.com. Thanks again

 

kevmor, I'll send them here shortly, they are on my laptop out in the garage. I'll send you both files, the one that I created with the exact orignal tables from by TBI truck ECM overlayed on to the LT1 program from my wife's '95 TA..the "normal" tables only were overlayed.
And the file I'm currently using that seems to work alot better with the higher hp motor...You'l be happy to know that I adjusted my speed calibration so the PCM sees the actual speed now and readjusted all of the tranny tables yesterday so you don't have to worry about the speeds being off that I mentioned before.

I'll send in 2 separate emails.

 

I thought that what you do not want is to lock up your converter when towing which was why an auto could pull more than a manual... Check that out.

 

Highlander, it gets tricky because you want to lock the convertor only to keep heat down, a slipping convertor produces a lot of heat, but at the same time, you don't want it locked while trying to accellerate with a heavy load if the motor can't tolerate it either, or heavy accelaration with it locked even if the motor can push it because that's hard on the convertor.
I haven't had a chance to tow much over the winter, but will be soon, so I'll be watching my trans temps carefully and will probably be making some adjustments, but with the cam I have, it tolerates locking the convertor in 3rd gear fairly soon, but if my TPS is over 40% (which means I'm accellerating) I don't lock it, only at cruise speeds with less than 40% TPS. I'm not going to tow in 4th, but I have the lock set very high in 4th gear, I think its set to like 60 mph or so.

 

check this out.. gm tells you to use 3rd gear (at least in my truck) for heavy towing. My GMC v6 doesn't lock the converter in 3rd gear.

 

Yep, because with the stock settings and lack of hp from a stock motor you can burn them up fairly easy. Engine hp must be able to handle and power a locked convertor also, otherwise it will sputter and spit thru the throttle body and it won't be able to turn the crank. My LT4 is outputting 364rwhp at around 4800 rpms, and about 270-300hp at 2400-3500rpms where you would need it on the street towing something. All comes down to watching the trans temps.

 

you can also do it programming.