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Thread: Beginner Questions

  1. #1
    Electronic Ignition!
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    Beginner Questions

    Sorry if these questions have been answered somewhere already or if it should just be common knowledge. I can't seem to find the exact answers I'm looking for no matter what different searches I do. I've been reading over many threads on tuning and VE tables and tutorials.
    I plan to do a 383 TPI engine build this year sometime and will be using 1227730 ecm with $8D bin. First time tuning and don't want to mess things up. Of course I plan to start small and learn as I go and right now I'm just tinkering with TunerPro and trying to grasp the concept of everything so I'll be ready to tune when the time comes.


    -In the bin there is an upper VE and a lower VE table. Assumingly this is off idle tuning and idle tuning.
    I understand the idea of driving around datalogging and filling history tables and adjusting upper VE through a spreadsheet provided by these forums. But how do you tune for the lower VE table? Is it the same idea as driving around except for lower rpms? Is it when idling in the driveway or coming to a stop?

    -Should the engine be in Closed Loop or Open Loop when datalogging and tuning for VE?

    -Do OL and CL BOTH run off the VE tables? I get a little confused about the o2 sensor or possibly tables being used only when in either CL or OL.

    -Do I need a wideband o2 for any reason?

  2. #2
    Super Moderator dave w's Avatar
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    Using Closed Loop data for tuning both upper and lower VE tables is a good plan.

    A wideband is a good tuning tool, not 100% necessary. The wideband provides good Open Loop information, Choke, Warm up, Acceleration Enrichment, and Power Enrichment.

    dave w

  3. #3
    Electronic Ignition!
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    So how is fuel calculated or tuned in open loop, say just after startup and on warm up?
    Is this just calculated between Displacement/Injector flow/MAP/TPS? Or does it use the VE tables?
    How do the Open loop % change afr vs temp/map tables work or affect the rest? I don't understand the values in those tables.

    A little more info:
    I'll be using a Speed Density 90-92 F-body 1227730 with $8D bin.
    Planning to build a 383 with FIRST TPI Intake, Brodix 1021007 Heads, Comp Cams 08-305-8 Cam, and will have around 10.3:1 static compression.

    Thanks

  4. #4
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    The $8D VE tables are indexed by MAP and RPM but are not throttle position dependent. Regardless of throttle position the lower table is used to 1600 rpm and the upper table is used above 1600 rpm.

    When the engine is running, fuel is calculated to deliver 14.7:1 AFR using VE, MAP, and CTS. Injector on-time is calculated using injector size and calculated fuel. There are small tables to tweak the fuel calculation and the injector on-time as well as separate tables used during acceleration enrichment. Open loop, cold start, and PE % change tables are used to richen desired AFR from 14.7. Closed loop is also a tweak to the original VE calculation based on O2 sensor signal input.

    Tuning with the engine in closed loop allows one to adjust the VE based on NBO2 feedback. We use the BLM and INT to scale VE so the O2 tweak is as close to zero as possible. This is good for warm, moderate driving conditions but does nothing for adjusting the open loop and transient conditions. Cold start, acceleration enrichment, power enrichment, and deceleration enleanment are part of the driving experience and if these are not tuned well enough the vehicle is no fun to drive. A heated wideband can provide feedback in a wider range of operating conditions. Logging WB readings allows one to drive the vehicle under conditions where the engine is misbehaving then evaluate the best path to correct the issues.

    At one time people were running into problems using $8D on high HP engines when the calculated fuel delivery time was too high. There is a fix that can be implemented in code. I believe that limitation is less a problem today as larger injectors with faster reponse times may reduce the need for large on-time values. Links to the problem and the fix are here .

  5. #5
    Electronic Ignition!
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    I highly appreciate you guys taking the time to explain some things. Your information definitely helps.
    Once I understand the basics and get going I should be fine. But I'm sure there is still years of learning to be done as well.

  6. #6
    Electronic Ignition!
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    So in the BLM Tuning Tutorial it says to disable the following:

    1. EGR
    2. PE.
    3. Air pump.
    4. DFCO
    5. Hiway Lean Cruise if applicable.

    What about AE? Does AE affect it and should it be disabled? If so, how?

  7. #7
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    AE will increase the delivered fuel for an amount of time. That time is often short enough that it will not affect BLM. When you are tuning based on viewing the amount of fuel burned you will naturally be viewing a combined total. But disabling AE makes for a very challenging drive. Every time you open the throttle the engine goes lean. So the question really comes down to how do you separate the AE from the VE. I have tuned with AE disabled and the final tune was very good. But I dedicated a *lot* of time to driving and accelerating slowly to see what would happen.

    AE should be tuned to cover the rapid changes that the ecm can't account for. Once the VE tables are right, a slow change in manifold pressure is no problem. But suddenly snapping the throttle open causes a massive change in pressure in a hurry so AE is used to provide additional fuel for the increase in air density. One approach is, when you have the engine operating and accelerating as you think it should be, to view the VE tables in a 3d axis. If the high load section at the end of the table seems too high or too low compared with cells nearby it suggests that the AE needs further adjustment. So shift some of the fueling toward or away from AE and rebalance the VE.

  8. #8
    Electronic Ignition!
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    Quote Originally Posted by 1project2many View Post
    AE will increase the delivered fuel for an amount of time. That time is often short enough that it will not affect BLM. When you are tuning based on viewing the amount of fuel burned you will naturally be viewing a combined total. But disabling AE makes for a very challenging drive. Every time you open the throttle the engine goes lean. So the question really comes down to how do you separate the AE from the VE. I have tuned with AE disabled and the final tune was very good. But I dedicated a *lot* of time to driving and accelerating slowly to see what would happen.

    AE should be tuned to cover the rapid changes that the ecm can't account for. Once the VE tables are right, a slow change in manifold pressure is no problem. But suddenly snapping the throttle open causes a massive change in pressure in a hurry so AE is used to provide additional fuel for the increase in air density. One approach is, when you have the engine operating and accelerating as you think it should be, to view the VE tables in a 3d axis. If the high load section at the end of the table seems too high or too low compared with cells nearby it suggests that the AE needs further adjustment. So shift some of the fueling toward or away from AE and rebalance the VE.
    That's a very good explanation, easy to understand and makes sense. Thanks!

  9. #9
    Electronic Ignition!
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    Okay I keep searching and still can't find clear answers and you guys have been helpful.

    The TPI is batch fire, correct? Does 1-3-5-7 side fire then 2-4-6-8 fire, or do all 8 injectors fire at the same time?
    The next thing I'm looking into is the injector duty cycle. Is there a formula I can use in the ADX file so I can have IDC displayed on TunerPro Dashboard, or do I just have to do the math on paper? I've seen different formulas online but they are all different in their own way and confusing. I also wouldn't know what to reference for sure with the 1227730 ECM and $8D. I checked the s_aujp files for anything related to IDC and didn't find anything. I'm not using s_aujp though, just stock bin/adx until I learn more.

    Edit:
    So okay the formula I came up with in the end is:
    (Injector Pulse Width X RPM)/600 = Injector Duty Cycle %

    Does this seem correct?
    Last edited by linville88; 02-09-2019 at 08:07 PM.

  10. #10
    Electronic Ignition! JimCT_9C1's Avatar
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    Injector Duty Cycle Calculation

    You are close, but not quite. Need to account for 2 engine revolutions per combustion cycle.
    Your factor of 600 should be 1200. Injector time in milliseconds, giving DC in percent.

    The time for 2 engine revs in msec is T = 2 * (60/RPM) * 1000 msec/sec

    Duty Cycle (%) = Injector Pulse width (msec) / Cycle time (msec) = t / T = ( t * RPM / 120000 ) * 100% = t * RPM / 1200


    Hope this helps -

    Jim

  11. #11
    Electronic Ignition!
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    Quote Originally Posted by JimCT_9C1 View Post
    You are close, but not quite. Need to account for 2 engine revolutions per combustion cycle.
    Your factor of 600 should be 1200. Injector time in milliseconds, giving DC in percent.

    The time for 2 engine revs in msec is T = 2 * (60/RPM) * 1000 msec/sec

    Duty Cycle (%) = Injector Pulse width (msec) / Cycle time (msec) = t / T = ( t * RPM / 120000 ) * 100% = t * RPM / 1200


    Hope this helps -

    Jim
    I'll be honest, you just confused the heck out of me. Lol.

    So do I just change it to:
    (Injector Pulse Width(msec) X RPM)/1200 = Injector Duty Cycle %
    Or would that still be incorrect?

  12. #12
    Electronic Ignition! JimCT_9C1's Avatar
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    Yes, just change 600 to 1200.

    Sorry about all the other stuff - just in case someone wanted to see the math.

    Jim
    1995 Caprice 9C1 LT1 - K&N Cold Air Kit, Dynomax Catback, 3.73s, Other Little Stuff

  13. #13
    Electronic Ignition!
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    Okay I think I understand it a bit better now. Another way of doing RPM math is there are 60,000 milliseconds in a minute. So 60,000/RPM = milliseconds per revolution.

    So the TPI injectors fire every 2 revolutions and not 1? I keep getting mixed answers across different forums and was under the impression all 8 injectors fire at the same time every revolution.

  14. #14
    Electronic Ignition! JimCT_9C1's Avatar
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    Glad you went through the math - Yes, I made an assumption of the injector firing once per two engine revolutions.

    I don't have the answer for TPI injector firing every one or two revs ... suggest you search and if needed post on the GM EFI subforum here
    http://www.gearhead-efi.com/Fuel-Inj...GM-EFI-Systems

    Both good searchable threads and knowledgeable people over there who I'm sure can help.

    Jim
    1995 Caprice 9C1 LT1 - K&N Cold Air Kit, Dynomax Catback, 3.73s, Other Little Stuff

  15. #15
    Carb and Points!
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    Tuning with the engine in closed loop allows one to adjust the VE based on NBO2 feedback. We use the BLM and INT to scale VE so the O2 tweak is as close to zero as possible. This is good for warm, moderate driving conditions but does nothing for adjusting the open loop and transient conditions. Cold start, acceleration enrichment, power enrichment, and deceleration enleanment are part of the driving experience and if these are not tuned well enough the vehicle is no fun to drive. A heated wide band can provide feedback in a wider range of operating conditions. Logging WB readings allows one to drive the vehicle under conditions where the engine is misbehaving then evaluate the best path to correct the issues.
    Last edited by dave w; 05-20-2019 at 03:22 AM.

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