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

  1. #16
    First post shows LT1/T56 swapped. If purge, egr and other things never run how would they cause issues? This is also the early LT1 ecm.

    On the flip side to all this, all the other ones that have been done were all manual trans and have been going strong for years now.
    Last edited by Skinny Pedal; 1 Week Ago at 11:23 PM.

  2. #17
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    Yes the egr and other emissions stuff have been disabled. I don’t think that will cause any issues.

    I’ll never hit what the ecu thinks is 100kpa because that would be 14 psi boost in reality (with 2 bar map). So I don’t think it will update on the fly.

    However it is showing a baro reading of 54.36. So last night was first couple passes at a NA tune with the 2 bar. Had to run the cylinder volume up to 1100cc to get close on fuel I guess since the ecu is seeing the air as very light ( which would require less fuel). That gets it running and driving. I can still use injector flow to further modify too if needed.

    I need to get the fueling closer so I can get back to open loop. It runs smoother open loop for some reason.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 32lb D3, LTs, garage ported

  3. #18
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    The baro update can happen any time the PCM would normally do a baro update, regardless of 100kpA, but it will happen automatically at 100kpA. You need to disable that.

    How are you retarding your spark?

  4. #19
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    Quote Originally Posted by Xnke View Post
    The baro update can happen any time the PCM would normally do a baro update, regardless of 100kpA, but it will happen automatically at 100kpA. You need to disable that.
    Is there any way to know when it would be updating the Baro? After tonight I'm not convinced the ECM is going to care, even if it does update. It's still going to just see 54.36. Now when boost is in the equation, what will happen? I have no idea.

    But I don't have a way to disable the auto update - at least not that I know of. Unless Tunercats can do it, which I don't have. I've looked a few times, and TunerPro doesn't seem to have a way to change the baro update programming. I'm kinda stumped on this one so far. Thoughts?

    How are you retarding your spark?
    Just using the standard tables. I charted the 1 bar vs. 2 bar readings out in excel and modified the table that way. Starting with 60kPa, just start pulling timing out. pull more at 70, more still at 80, and so on. All values over 55 in the table will be "boost" (since 55 on the 2 bar MAP is 100 on the 1 bar map), but the ECM doesn't really know, it's just using the tables as designed based on MAP reading.

    I had the car running and driving pretty nice tonight on the 2 bar tune. CHanges for tonight were just to max out the cylinder volume, and reduce injector constant to 28 (have 32lb injectors) to richen enough. I'm not exactly sure what other gremlins are waiting for me on this. At least in NA trim, it seems to be just fine. I think by modifying the PW calculation this way, it's compensated for the low baro reading. Can anyone confirm that makes sense?
    Last edited by hotrodf1; 1 Week Ago at 06:02 PM.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 32lb D3, LTs, garage ported

  5. #20
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    Baro updates, at least in the P66 codes, happen at a maximum RPM that can be set, and 100% throttle. So for example, the factory settings for the 3.4L camaro is 4000RPM, so with the stock throttle body, at anything under 4000RPM if you went 100% throttle, it would take a barometric reading. If you're under boost when that happens, all your un-boosted fueling will be significantly affected. There are (in the 3.4L camaro code) 25 parameters that are affected by the barometric readings, including: altitude correction to MAP, MAP sensor offset, IAC steps multiplier vs baro, A/C added IAC steps multiplier vs baro, barometric correction to accelleration enrichment, barometric multiplier for power enrichment threshold, fuel pulse width multiplier vs baro.

    In tunerpro, you can do a ctl-F to search for any parameter with BARO in the name to pull all the ones you need to consider.

    I don't have DA3 or EE up in front of me right now, but I do have the v6 version from the same years code pulled up-that's what I'm working on.

    Also, when you did your scaling did you take into account the different MAP sensor offsets?

    1 bar sensor has a 10.3kpA offset, 2 bar is 8.8kpA. So, your ADC counts (what the PCM is using the actually do the fueling) would be (offset - minimum readable pressure) / ((max readable pressure - minimum readable pressure)/255) If you didn't take that into account, it could be a problem later. The computer doesn't read kpA, or even volts, it reads ADC counts...so a 0-5V sensor has 255 discrete steps, minus 0 and 255, that are usable.

  6. #21
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    Question Reference pics attached

    Quote Originally Posted by Xnke View Post
    Baro updates, at least in the P66 codes, happen at a maximum RPM that can be set, and 100% throttle. So for example, the factory settings for the 3.4L camaro is 4000RPM, so with the stock throttle body, at anything under 4000RPM if you went 100% throttle, it would take a barometric reading. If you're under boost when that happens, all your un-boosted fueling will be significantly affected. There are (in the 3.4L camaro code) 25 parameters that are affected by the barometric readings, including: altitude correction to MAP, MAP sensor offset, IAC steps multiplier vs baro, A/C added IAC steps multiplier vs baro, barometric correction to accelleration enrichment, barometric multiplier for power enrichment threshold, fuel pulse width multiplier vs baro.
    First: what represents 100% throttle? on TPS% or MAP reading? GUessing TPS %.

    So it sounds like my safest bet is to somehow take that RPM for the update and just run it up to 7000 or something that I won't be hitting. How in the world do I do that, if it's not an option in the $DA3 mask I have on TUnerPro? I do have a couple other ones from other sources, but pretty sure they have even less, I'll check anyway. I'm somewhat new to tuning, this LT1 was the first I've tuned that didn't have a carb, LOL. So to do a binary editor or something, I just would have no idea where to start to be honest.

    I think I dealt with several tables that have a baro reading, or MAP reading, but if it updates to something other than 54 ish kPa, I can see that it will likely get really rich. Which would mean I'd have to shut the car off, then restart to reset the baro reading, and get it back home. I haven't bought all my turbo stuff, so was trying to get the 2 bar tune worked out somewhat before I spent the money.

    In tunerpro, you can do a ctl-F to search for any parameter with BARO in the name to pull all the ones you need to consider.
    Ok I'll try that

    I don't have DA3 or EE up in front of me right now, but I do have the v6 version from the same years code pulled up-that's what I'm working on.

    Also, when you did your scaling did you take into account the different MAP sensor offsets?

    1 bar sensor has a 10.3kpA offset, 2 bar is 8.8kpA. So, your ADC counts (what the PCM is using the actually do the fueling) would be (offset - minimum readable pressure) / ((max readable pressure - minimum readable pressure)/255) If you didn't take that into account, it could be a problem later. The computer doesn't read kpA, or even volts, it reads ADC counts...so a 0-5V sensor has 255 discrete steps, minus 0 and 255, that are usable.
    I think so. Here's a snip of what i did, maybe you can give it a look and see if it makes sense. I found equations for voltage vs. MAP reading for both MAP sensors. So I took the 1 bar reading, then converted to volts. Then took each voltage and converted to the 2 bar equivalent reading. (see first pic) It seems to be working well, my old VE tables were modified according to this, and when I ran closed loop to get a read on BLMs, I'm seeing a pretty nice even display, so it would seem whatever offset has in reality been taken care of. Not sure, just trying to logic my way through
    Attached Images Attached Images
    Last edited by hotrodf1; 1 Week Ago at 06:50 AM.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 32lb D3, LTs, garage ported

  7. #22
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    Well I'm happy to report that the 2 bar MAP tune is working well with the motor running NA.

    THe most immediate concern I have now is just the inability to turn off the barometric updates in the ECM. Could someone at PCM for less solve this for me perhaps?

    I tried looking through the $DA3 disassembly, but that's way over my head to even attempt to figure out where I'd need to go to add that variable in TunerPro. Any ideas out there?
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 32lb D3, LTs, garage ported

  8. #23
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    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!)

  9. #24
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    Need help with Baro update issue!

    Quote Originally Posted by Xnke View Post
    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
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 32lb D3, LTs, garage ported

  10. #25
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    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.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 32lb D3, LTs, garage ported

  11. #26
    Fuel Injected! steveo's Avatar
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    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

  12. #27
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    $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.

  13. #28
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    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

  14. #29
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    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...

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