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Thread: E38 VVE Setup Guide

  1. #61
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    Swingtan, ive got some questions about your methods that I don't agree with (or maybe I don't see the light yet)

    First you change all your IAT modifiers to 1, effectively removing any effect IAT has on AFRs.

    But then you go log your AFRs and compare them against your IAT and when you see that there off, you fix this by modifying the flow rates of the injectors.
    Is this not fudging big time?

    Isn't this drift in AFRs caused by the density change of air, eg higher temps, means air is less dense, less dense air has less molecules, less molecules of fuel with same amount of fuel causes it to go lean, which you seen in your IAT vs AFRs.

    So shouldnt the IAT table be modified instead of fudging the injector flow modifier?

  2. #62
    Lifetime Member swingtan's Avatar
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    Pauly,

    You need to stop, sit and think about how tuning with the computer differs from playing with carby jets and distributor weights. You may not agree with everything, but sometimes it's because you may not understand. here's a very basic rundown of the basic tuning principles when dealing with a computer managed system.

    1. Understand the current system and how it works: The computer managed system is much, much more complicated than distributors and carbies. When dealing with physical devices, it's easier to see how they work and what effects changes will make. It doesn't work the same with the computer.
    2. Understand what the settings in the tune file do and how they effect each other and the final engine management: Many tables are cross referenced with other tables. Settings turn off / on entire sections as well as alter settings under different conditions.
    3. Start tuning by "base lining" the engine: Because of the complexity of the management system, you MUST get the basics right. Sure you can go out one day and fudge the fueling tables to look right for that day, but if conditions change, the fueling will probably go right out.
    4. Make small and calculated adjustments: Pretty self explanatory really.
    5. Make one or two adjustments at a time: Again, std tuning rules. Change too much and you have no idea what helped, if anything. Maybe one change helped and one made things worse and they canceled each other out.
    6. Never assume that what you think is correct, especially when starting out: You will see people on here that have been tuning for many years asking basic questions again, just to be sure. There is no shame in this, we all forget things. It'd be much more embarrassing to get something wrong and damage a motor.


    Now, getting back to your slightly sparse questions....

    1. When you talk about IAT modifiers, I'm assuming you mean {B0146}. You didn't specify so I'm guessing.... This table is used to add commanded fuel depending on the IAT. In certain circumstances, you want to alter the commanded fuel, especially at cold starts. So you can richen up the commanded fuel with this table. You don;t really want to be commanding lots of different AFR's when setting up the VVE as it just makes thing more confusing, so you set it all to 1 to ensure it doesn't move things around on you.
    2. Is it fudging? No, you couldn't be more wrong in this case. When adjusting the Injector Flow Rate vs IAT, you are correcting the supplied fuel amounts for what the engine needs. You are measuring the exhaust AFR's with the WB and adjusting the flow rates to ensure that the actual AFR matches the commanded AFR. If you used {B0146} to correct this drift, THEN you would be fudging the tune as you have not matched the commanded vs exhaust AFR's just altered the commanded to get the value you wanted.
    3. Yes, as the IAT increases, the air is less dense so less fuel is needed.
    4. No, the IAT table should be used to "command" a different AFR depending on the IAT. It should not be used to "correct" the mixture because other parameters are out of calibration.


    Simon.

  3. #63
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    Arh simon, sorry I understand now. Your answer and an answer to another post of mine cleared this up for me.

    I thought the IAT scalar was a scalar that is used to calculate the mass of air, ie when its hotter the air is less dense and hence less mass of air for same given volume. But this is not the case, as you mentioned the IAT scalar is just used to command different AFRs (like for a choke on cold mornings)

    What I was thinking the ECM does automatically when it looks at the VE table, having values of g.K/kPa, it multiplies this by temp and divides by pressure to give mass of fuel. I thought by scalaing the IAT table to 1, you are removing this step the ECU does to work out the mass of air, but I was wrong.

    Things are much clearer now, thanks.

  4. #64
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    Why do you have to disable the fuel trims when you force the car to stay in OL mode? If your in OL mode I thought the trims don't work anyways.

  5. #65
    Lifetime Member swingtan's Avatar
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    They are the same thing, do one and you do the other.....

    IE. Disable STFT = OL mode

  6. #66
    Lifetime Member swingtan's Avatar
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    Quote Originally Posted by pauly24 View Post
    Arh simon, sorry I understand now. Your answer and an answer to another post of mine cleared this up for me.
    Lol.. I read that whole post with a Pirate voice :p

  7. #67
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    hahaha, laughing at my stupidity aswell, I've read over your tute so many times. Don't know how I thought they were different, its clearly obvious. Thanks.

  8. #68
    Joe (Moderator) joecar's Avatar
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    Links for easy reference:
    E38 VVE Setup Guide
    Virtual VE Tutorial
    Last edited by joecar; September 6th, 2011 at 04:29 PM.

  9. #69
    Senior Member Dieselman's Avatar
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    Hello everybody,

    Well I finally got around to setting up my wideband and did a bit of logging but I think I stuffed up on the PID selection.

    I selected GM.AFR instead of E38.AFRATIO

    Is there anyway I can save this log or is it toast???

    If anyone can see what else I am missing a few pointers would be appreciated. I am using a Tech Edge 2J2 wideband with a serial connection and tuning a L98 VE Commodore


    Thanks in advance
    Attached Files Attached Files

  10. #70
    Lifetime Member swingtan's Avatar
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    Well....

    You only have 22 min worth of log data there, so you are going to be cutting it close to the minimum amount of data needed. I prefer to run logs of over 30 min, preferable over 60min when using street based logging. On the dyno you can use a much shorter log as you can hit the required cells more often. However, you can still use this log even though you didn't log E38.AFRATIO.

    What I'd do is check the tune settings for PE mode, and then filter out PE mode in scantool. You can then assume that the commanded AFR will always be stoichiometric ( or what ever was commanded, but it'll be fixed ). So you can make a custom PID to display a fixed BEN Factor for the commanded AFR vs the WB reading.

    Then invert the filter and do the same for PE mode, as if you set up PE as in the tutorial, then it should be a fixed setting as well. If you get really tricky, you can make a custom PID to work with both cruise and PE mode in one hit.

    It's a bit of work though and would be a little tricky, but it could be done. Or just redo the log using the correct PID's. I was talking someone else today about this and mt suggestion was to log the drive to / from work for a couple of days and then use the log joining tool to combine them into a single log. Then after filtering the data, use the combined logs to apply the changes to the VVE. When getting log data, keep changing gear up and down to vary the RPM and load, this gives lots of good data.

    Simon.

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