pcmhacking.net

The 411 PCM has a few pins that were used as inputs and outputs for sensors and actuators in automatic transmissions, and I'm wondering if those pins could be put to more interesting uses in manual-transmission cars.

According to the pinout at http://www.lt1swap.com/99-02_vortec_pcm.htm

Blue connector pins:
17 - trans fluid pressure switch b (presumably a binary input)
18 - trans fluid pressure switch c (ditto)
32 - PRND "A" input (not sure if digital or analog, likely digital)
24 - PRND "P" input (apparently binary, park/neutral)
79 - 2/3 shift solenoid control (what kind of control signal? binary, analog, PWM, etc?)

Red connector pins:
2 - TCC control solenoid (what kind of signal?)
6 - transmission fluid pressure control solenoid high (what kind of signal?)
8 - transmission fluid pressure control solenoid low
47 - transmission shift solenoid A (what kind of signal?)
48 - transmission shift solendoi B (what kind of signal?)
51 - transmission temperature signal - ?

The web page says this last pin is used only for AT, but I have a hunch my MT Corvette might use it for the transmission temp display in the instrument cluster.

If the solenoid outputs are PWM then one of them could presumably be re-purposed for boost control on forced-induction cars, with some hacking of the PCM firmware of course. Since the PCM knows throttle, RPM, and vehicle speed, one could presumably set up per-gear boost control tables.

An analog could potentially be re-purposed for use with an ethanol sensor for flex-fuel, again with some firmware hacking.

A digital input could be re-purposed as a valet switch to limit throttle on drive-by-wire cars to, say, 50%. Or limit RPM to 4000 on cable-throttle cars.

But since I've never paid much attention to how automatic transmissions work, I have no idea what sorts of signals these I/O pins were intended for. Does anyone know?

And while I realize that it's kind of early to start talking about this degree of firmware hacking for these PCMs, I'm pretty optimistic about the near future.

Personally I think there would be 3 main features that would cover what a lot of people would want. The first would be a 2step/ wot no lift shift. The second would be a way to pull timing with a input for nitrous. Third would be boost control. I believe these 3 would cover a lot of what the average gear head wants and needs. Also I think 0411 is flex capable already. I could be wrong but I know there are people doing it. I was thinking that the po1 or 0411 pcm is only capable of 2bar osd with flex but the p59/1mb pcm is capable of 3 bar osd and flex. This could just be hptuners limitations also not for what you are looking to do maybe.

The 1mb PCM is very under utilised. It could be enhanced a great deal.

cjcalhoun85 wrote:Personally I think there would be 3 main features that would cover what a lot of people would want. The first would be a 2step/ wot no lift shift. The second would be a way to pull timing with a input for nitrous. Third would be boost control. I believe these 3 would cover a lot of what the average gear head wants and needs. Also I think 0411 is flex capable already. I could be wrong but I know there are people doing it. I was thinking that the po1 or 0411 pcm is only capable of 2bar osd with flex but the p59/1mb pcm is capable of 3 bar osd and flex. This could just be hptuners limitations also not for what you are looking to do maybe.

Boost control is really the main reason that I started this thread - to implement that in the PCM we'll need a variable output. Preferably PWM that we can just directly hook up to a boost control solenoid, but an analog output could probably also be made to work without too much trouble. I'm hoping that one or more of these AT outputs can be used for that purpose, but I don't know enough about them, which is why I'm asking.

I added a no-lift-shift rev limiter to my Subaru, there are a bunch of Subarus out there now running code that was derived from mine. We also have a configurable rev limit for launch control. Clutch + brake + stopped = 4500 RPM limit; clutch + WOT + moving = 5500 RPM limit. Otherwise, stock rev limit. All of those limits are tunable of course. I'm sure the same can be done for 411s as well. Nitrous is rare in the Subaru world, but pulling timing in response to an external signal sounds easy enough. (And if I remember right, people are already doing that with GM V8s by interrupting the intake air temp sensor signal and tweaking one cell in the IAT compensation table to pull timing when the signal is lost.)

I agree that the 1mb PCMs might be a better choice for all of this. If anyone knows how those PCMs control automatics, I'd love to hear about that. I am pretty sure we'll have 411 reflashing first, but hopefully the 1mb PCMs won't be too far behind. We'll see.

This all sounds great I hope you all keep at it.
I have some 1mb pcm files here in BIN format if it helps at all?

Here is some info to look at. http://www.msgpio.com/manuals/mshift/wiring.html

Thanks for that link! It sounds like most of the outputs are switched, but the pressure control solenoid may be suitable for boost control if it's ~300hz PWM like the MS GPIO.

NSFW wrote:Thanks for that link! It sounds like most of the outputs are switched, but the pressure control solenoid may be suitable for boost control if it's ~300hz PWM like the MS GPIO.

The TCC PWM output could probably be fooled into working as long as you're using a manual/non electronic trans and the boost control solenoid would have to accept the PWM frequency in use.

There are 2 tables for TCC duty cycle in an 0411/P59. TCC minimum DC % and TCC maximum DC %.

The tables reference commanded line pressure along one axis, and transmission fluid temp along the other. You could potentially fool the PCM trans fluid temperature up and down. and then use commanded line pressure as a way to limit boost up top. I'm sure theres many other ways you could do it. On an auto trans vehicle with a decent stall converter I will set the max duty to 99% and the minimum duty to 75% to prevent too much slip on lock. You can adjust the apply rate also.