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

  1. #1
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    2 bar tune for Turbo LT1 F-body possible with '93 ECM? DA3

    Trying to decided to take the plunge on a 76mm On3 turbo for my LT1/T56 swapped third gen F body.

    I'm shooting for a low-boost 5-7psi for a fun street car. Motor is stock lower end, ported heads, 224/224 cam.

    I have the unique to '93 LT1 ECM, and have tuned it myself with TunerPro RT and the Moates setup. I'm currently running dedicated open loop, and feel pretty solid with that.

    What I'm wondering is, can I install a 2 bar Map sensor and make the stock ECM work for this turbo application? Is there another GM ECM that would work better for this?

    Is there a way to make TunerPro show 0-200kPa like the sensor will be reading, or do I just need to do the conversion by hand (50kPA on screen = 100kPa real life)?

    I'm assuming I would need to "truncate" the VE and timing tables from 0-100kPa, then be very cautious going from 100-200kPa and sneak up on a safe tune little by little.

    Do any of these assumptions ring true, or am I asking for trouble doing this?

    I know that's a lot of questions in one post, sure would appreciate any feedback out there. Thank you!
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  2. #2
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    No, the LT1 PCM does not and as far as I have been able to find, can not support the 2-bar map sensor. It was a similar situation with the P66 6-cylinder PCM and I thought after doing that one, that the $EE PCM could be done too-but apparently there is some trickery needed that doesn't work.

  3. #3
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    I thought I read though where a 2 bar MAP sensor voltage range is still 0-5V, but instead of 0-100kPa, its now 0-200kPa, unless I'm totally confused. So the ECM shouldn't care, since that fits into its range?
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  4. #4
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    Happened upon this thread too.
    http://www.gearhead-efi.com/Fuel-Inj...Turbo-LT1-Tune

    So apparently he was able to do it. But on $EE which would be a flashable PCM in the 94-96 F Body etc.. Not really sure how different that is from $DA3. I'm cautiously optimistic . . . .
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  5. #5
    Not hard. Just remember to scale everything.

  6. #6
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    Cool I think I’ll get a 2 bar map and try to set everything up NA to prove to myself I can do it!
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  7. #7
    Awesome!!! If you need any help just ask.

  8. #8
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    I do have one question to start with. Since the VE tables only go to 100, I need to rescale by some factor, correct? The motor wanted more fuel even in NA trim, so I recall that I bumped the cylinder volume up about 10% or so, and then scaled all the VE tables down by 10%, thus gaining headroom for more fuel.

    Is this the right way to go on a turbo motor as well? So then I'd bump the cylinder volume up by say 40% or so, then decrease the VE tables by 40%? Or is there a better way? I know you could use injector flow too. ??

    I'm running Open loop, so I use the % change fuel vs. MAP sensor table which has worked out well in NA trim - I could use that to dial up the fuel too I guess, since the kPa range will affect that table. Any thoughts 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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  9. #9
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    How to disable barometric refresh in $DA3? Using BDLD bin

    I have another question too, I read that I need to disable the barometric refresh / sensing or something of that nature when I go to the 2 bar sensor. I have noticed the ECU has a separate reading for barometric pressure and MAP, but perhaps it's coming from the same sensor?

    i'm not sure I've got that capability to turn off in TunerPro RT. I don't see anything like that in the variables that I have to play with. So if I can't do something with that, am I screwed trying to get to a 2 bar tune with the stock ECU on $DA3?
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  10. #10
    Map and baro come from the MAP.

    Is your fuel pressure reg boost referenced? This will have a huge effect on VE table in boost. Scaling the VE for a 2 bar is not hard to start. Copy your 100 kpa to 50 kpa..... and so on. Leave 55 and up flat from the 100 column and bump it if you like, that depends on regulator.

  11. #11
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    1 bar vs 2 bar MAP.jpg
    Quote Originally Posted by Skinny Pedal View Post
    Map and baro come from the MAP.

    Is your fuel pressure reg boost referenced? This will have a huge effect on VE table in boost. Scaling the VE for a 2 bar is not hard to start. Copy your 100 kpa to 50 kpa..... and so on. Leave 55 and up flat from the 100 column and bump it if you like, that depends on regulator.
    Yes, the FPR is the stock unit, and will be boost referenced, I believe, 1:1. I run in open loop, so I can use the open loop % fuel adder vs. MAP signal to add fuel "across the board" in addition to the VE tables. I have a wideband so tuning in boost area should be OK, just gotta sneak up on it.

    I think I have the scaling figured out for the most part. Made a chart that tells the old vs . new MAP reading. It isn't actually 1:2 ratio which is interesting. But like you said 55 (2 bar) ends up being 100 (1 bar). 40 (1 bar) is 70 (2 bar). Attached a pic that shows my conversion table.

    The thing that's the biggest question for me: what does the ECM do with the baro reading when you turn the key on? If it used to be 100 or so with the 1 bar sensor, now it's going to be 55 ish kPa with the 2 bar sensor. What's that going to do to the tune? Do I just need to find another table to scale somehow so that the computer still calculates the same results for fueling or what?

    I don't have $EE so I don't have quite the same parameters list as that. The $DA3 isn't as well researched and pulled apart I think.
    Last edited by hotrodf1; 07-01-2018 at 10:58 AM. Reason: pics
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  12. #12
    The open loop fuel adder, IIRC, is the commanded open loop AFR. Can you post up the file you will be starting with?

  13. #13
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    BIn and XDF attached

    Yeah no prob. Modded bin, XDF, and stock bin JIC

    The table I'm talking about isn't commanded AFR I don't believe. I think it just adds fuel on top of the VE table, of course only when in open loop. Sort of a PE mode, without going into PE mode. I have that disabled too. Maybe I shouldn't?

    The 2 bar MAP came in today. Guess I'm going to see if she'll run NA with the 2 bar MAP.

    Still not sure what to do about the Baro update deal. Maybe it won't even matter.BDLD 93 Z28 M6 R34 2 BAR MAP.binDA3.xdf
    Attached Files Attached Files
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  14. #14
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    Hmm, didn't attache like I thought
    Attached Files Attached Files
    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, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

  15. #15
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    Hope you don't have a 4L60E in there.

    The reason you can't do this with the 2-bar map isn't fueling. It's that EVERYTHING in the trans code relies and absolutely needs that 1 bar map sensor, or you're gonna have to re-code all the transmission line pressure and shift timing sections. On top of that, you have to overcome the barometric update issue-I have the same issue with the P66 code in the 94/95 V6 computers. I have to run with the barometric update completely disabled, and had to create a new MAP sensor conversion to report accurate pressure, and then create an emulated 1 bar MAP value to pass off to the transmission code. I'm still (two years later) working out the last few bugs of JUST the emulated 1bar MAP sensor, and the small group that started the project had to work in an extremely tight code limit.

    The 2-bar sensor does use the same 0-5v range, but it uses a different linear equation to convert from a 0-255 value to the 8-200kpA value. You'll need to find the ADC sample code, hijack the ADC code's output and run it through your new equation, fork if greater than 100kpA so you can set a flag that tells the PCM you're in boost, use the boost tables, and then unset the flag when you drop under 100kpA. At the same time, create an emulated MAP value to send to the T-side of the pcm to allow transmission controls to function, and keep some of the other stuff (air conditioning) working properly. Then, you'll need to create a second set of VE and Spark timing tables to use when the 100kpA flag is set. Then, you'll need to deal with things like the EGR, purge solenoid, baro update, MAP sensor fail mode, etc all still work...even if you are not using them, the PCM code is there and it WILL try to use them. This can cause MAJOR issues, especially the EGR and Baro update problems. EGR will change your spark timing and targeted AFR, and if you were to get a baro update (which will happen immediately upon hitting 100kpA) it would reset the baro pressure to 100kpA, altering your base fuel and your boosted fuel maps.

    There is a lot more than just halving/shifting tables around.

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