2 bar tune for Turbo LT1 F-body possible with '93 ECM? DA3

[Xnke]

It's been talked about in the $EE code for a long time, but something was in the way-I am not sure what it was. I know the RPM limit is hardcoded and would require a major code redesign if you wanted to go higher than the factory PCM's max RPM (not the stock engine redline, but the "PCM" redline...) and I think the 2-bar MAP swap was something similar. Hopefully this thread will result in a proper 2-bar support for the LT1 PCM...there are a few old Nissan V8's that could REALLY benefit from this (they used a distributor with a timing output identical to the optispark!)

[hotrodf1]

It's been talked about in the $EE code for a long time, but something was in the way-I am not sure what it was. I know the RPM limit is hardcoded and would require a major code redesign if you wanted to go higher than the factory PCM's max RPM (not the stock engine redline, but the "PCM" redline...) and I think the 2-bar MAP swap was something similar. Hopefully this thread will result in a proper 2-bar support for the LT1 PCM...there are a few old Nissan V8's that could REALLY benefit from this (they used a distributor with a timing output identical to the optispark!)

I'm pretty sure the $EE code has the baro update feature worked out already. I think skinny pedal said he was able to turn it off.

That being said, if someone was sharp, it seems as if they could use the code in $EE to find where it's buried at in $DA3, maybe it looks similar. Might be way off base on that. Again, over my head at this point.

I think I'm at the point where I'm just gonna have to try it and see what happens. Then, if it doesn't work. . . . I"m not sure what I'll do. LOL

[hotrodf1]

VS Racing 78/75 turbo on the way. Intercooler, BOV, wastegate, oil lines, etc. here already. Still have to figure out the hotside, which isn't the easiest thing, but I have some ideas.

Hoping the baro update deal doesn't bite me too hard.

[steveo]

aww come on this is dumb, lets just find the DA3 barometric update parameters!

there's a disassembly of DA3 that's partially completed in the $DA thread

tracking down the routine for updating barometric pressure would just take some digging.

since we don't know where baro is stored but have a gigantic pointer (the datastream message contains baro volts) go backwards from the datastream message to determine where barometric pressure volts are stored in memory

then figure out anywhere that modifies that byte using a non-static value, you'll find the subroutine for baro update pretty quickly that way, probably right next to where TPS is compare to a static value, which will be your baro update tps %.

i'll look at it later tonight if i have time

[steveo]

$003F is the memory address of baro pressure volts

at C366, we see:

C366 : LDAA $00DA
C368 : STAA $003F

00DA is the map pressure (isn't it cool they put a speed density ECM's MAP memory address the same as its mask? im probably the only one that finds this cool.)

this is probably inside the barometric update subroutine, now just need to analyze the conditions and branches that reach this code to figure out how to disable.

or be super evil and just patch 'er like this:

C366 : LDAA $003F
C368 : STAA $003F

also found this,

E5E4 : LDAA #$FF
E5E6 : STAA $003F

this is probably a barometric initializer, sets baro to max, perhaps set this to $7F for a 2 bar system?

more research required.

[hotrodf1]

$003F is the memory address of baro pressure volts

at C366, we see:

C366 : LDAA $00DA
C368 : STAA $003F

00DA is the map pressure (isn't it cool they put a speed density ECM's MAP memory address the same as its mask? im probably the only one that finds this cool.)

this is probably inside the barometric update subroutine, now just need to analyze the conditions and branches that reach this code to figure out how to disable.

or be super evil and just patch 'er like this:

C366 : LDAA $003F
C368 : STAA $003F

also found this,

E5E4 : LDAA #$FF
E5E6 : STAA $003F

this is probably a barometric initializer, sets baro to max, perhaps set this to $7F for a 2 bar system?

more research required.

Like all this, how do I learn about all the code etc.? Might as well be Chinese.

[steveo]

if i'm reading it correctly this routine ensures baro is never less than map (should never happen in an n/a engine) so i guess it's a keep-alive separate from update? we might want to nerf it for a turbo system too.

A3CF : LDAA $00DA
A3D1 : CMPA $003F
A3D3 : BLS $A3D7
A3D5 : STAA $003F

[Xnke]

Setting the baro to be equal to baro is not a bad plan, but you just need to update that baro value on startup only. Once the baro value is worked out, next on the list is gonna be making sure the auto trans code doesn't cause problems in a manual transmission application, (could freak out about map greater than 100 and cause issues in other parts of the code) and EGR routine stuff (even if EGR isn't hooked up, it modifies the spark tables), and then working out how to get good control of the spark tables and timing retard due to engine knock tables. This stuff shouldn't be too hard, but it will be important.

Just like boosting the P66 code has resulted in air conditioning weirdness...I totally forgot to post that stuff I told Ku4o I'd post last week...

[steveo]

i can dig into other stuff that uses map to see if adjustment is necessary

i'd like to say we can set baro to a static value for a boosted engine, assuming it isnt going cross country (or maybe even if it is)