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Thread: GenIII EOI fuel timing

  1. #1
    Advanced Tuner Bluecat's Avatar
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    GenIII EOI fuel timing

    Several things have always aggrovated me about the GenIII pcms. Not having source code for the os's, certain things are either unknown or you have to take someone's else word on how it works. Unlike the days of old when it was reasonable for a professional like myself or even a hobbiest to break apart a 16k bin and know what every byte did, things are to big and complicated to handle like that anymore. Thats why we pay companies like HPT the big bucks to do it for us.

    It may not be reasonable for me to spend the time to reverse engineer the thousands of gm os's that exist, but I decided that it was for me to build a benchtop stimultor to simulate a running engine and function as a digital scope to watch outputs.

    Anyway, with the racing year slowing down I finally found a little time to devote to my project. Took a CStamp packing a 40mhz PIC18F6520 and layed out and built all my hardware. Wrote all the software for the microcontroller and then wrote an app to control and communicate with it on the PC side. Couldn't find any data on the event timing on the 24x/1 signals so I took an pigtail wired with a led and read the timing patterns off an engine that we just got back from the machine shop. Here is the data I read incase anyone else would like to have it. 24X-1X.xls







    I'd never seen a definative answer on what the units for eoit tables really meant, so that was the first thing I wanted to tackle. I'd heard everything from 15,33,45 on the reference periods, much a less what starting point the bondaries were relavent from. So after much flashing and observing, I compiled a data sample only to discover that a reference period is actually 90 degrees. The normal and boundary are added together like we were told. but the starting point appears to be some non natural point long before the engine cycle. Also the makeup numbers seem to have no effect. If the code is actually functional, there must be a master switch that has it disabled because no matter were I put the makeup numbers I never observed more than one fuel pulse per engine cycle. Here is the data I recorded.

    Observed_FT.xls

    The only formula that I could come up with that fit all recorded data was -784 + ((Boundary + Normal) * 90). That puts the stock settings yeilding an eoit of 300 degrees ATDC compression, which makes sence. That also means the max that it can be retarded is 656 ATDC if viewed as a 720 engine cycle. Which is all the range we need since for somthing like an G5X3 the exhaust is closed by 390 and the intake by 610. Which before I was always conserned that if the units were 45 degrees or less than 8 + 8 wouldn't allow enough range to delay any of the fuel after the exhaust had closed.

    Don't know if this helps anyone, but it makes me feel better about what I'm changing and tying to rationalize the results I've had from boundary changes.
    Last edited by Bluecat; 11-24-2010 at 01:53 PM. Reason: grammatical

  2. #2
    Advanced Tuner Bluecat's Avatar
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    I really figured more people would have a comment on this. I know I spend a lot of time out of the circle so to speak and in turn spend a lot of time "reinventing the wheel". Did everyone already know that the eoit reference periods were 90 degrees?

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    Senior Tuner LSxpwrdZ's Avatar
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    I'll be honest there are alot of people on this board that wouldn't understand a single word you said haha. You'd literally have to show them with a screenshot of the table in the editor probably.

    I know we talked about this on the phone the other night but great work! I wish I had the electrical engineering and programming knowledge you've got!
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    Advanced Tuner Bluecat's Avatar
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    Thanks for the kind words my man. Now get off the computer and go pull some weight out of that car of yours. You've got a date with the 8's come spring...

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    Very interesting! I've always wanted to explore this more but without real units or a description on how exactly it works I have been reluctant to try it. I don't know what we should expect here but I have first hand experience where moving injection target on a full race engine and it made a 20-30 fly wheel hp difference. The problem is on that project the target was not defined clearly and on top of that moving it to a place that was a little backwards in our logic made the gains.

    Here is a request, Do you mind making a 0-720 degree graph showing start and end of injection and TDC P/TDC E I think that will make more since for more people.
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    Senior Tuner Higgs Boson's Avatar
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    I kind of had a feeling based on exhaust smell.

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    Quote Originally Posted by LSxpwrdZ View Post
    I'll be honest there are alot of people on this board that wouldn't understand a single word you said haha.
    I'm in the same boat...anyway, with just a single sentence: is this somehow related to an injector timing?

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    Senior Tuner LSxpwrdZ's Avatar
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    Quote Originally Posted by Bluecat View Post
    Thanks for the kind words my man. Now get off the computer and go pull some weight out of that car of yours. You've got a date with the 8's come spring...
    Man I hope so but prolly wont happen on a DOT tire... haha

    Quote Originally Posted by Pekka_Perkeles View Post
    I'm in the same boat...anyway, with just a single sentence: is this somehow related to an injector timing?
    Yes this is completely about injector timing. Basically with different camshafts and valve events the factory fueling injector timing is slightly off. It varies from car to car because of camshaft size and timing. If a man knew exactly what angle the valves open and close you could map out when the injector should fire and finish. The settings are for End of injection pulse so different size injectors are going to play a role in finding the sweet spot as well. This is one reason why that 80% max duty cycle is a sweet spot because it has the injector staying open for the most time each stroke to better atomize the fuel.

    This is also another way to get the fuel smell down on larger overlap camshafts.
    James Short - [email protected]
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    Good information.

    With an operational simulator and known cam events you can find the sweet spot before you even fire the engine.

  10. #10
    Tuning Addict WS6FirebirdTA00's Avatar
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    Very interesting read, thanks for your work!
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    I have a feeling this thread and the other on this subject are going to get very interesting real soon.

  12. #12
    Advanced Tuner blownbluez06's Avatar
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    Quote Originally Posted by WS6FirebirdTA00 View Post
    Very interesting read, thanks for your work!
    I agree.

    Now I just need to sit down and figure how to apply this to my tune to achieve optimum injector pulse timing. I had read a comment that Google made regarding gaining power on the dyno by changing the boundary value (which forced him to retune the VE), but never understood the what the EIOT values meant. I guess I would consider taking this information and finding the stock Z06 valve timing and compare it to my current cam's valve timing and make an adjustment accordingly and measure the result. Thanks for your contribution!!
    Last edited by blownbluez06; 01-04-2011 at 11:27 PM.
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  13. #13
    Tuning Addict WS6FirebirdTA00's Avatar
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    The bigger problem I see here is the risk/reward. Later injection will insure you have less just passing through the exhaust but also runs the risk of washing the cylinders down. Too early and now you are passing even more though the exhaust, but can spray to the back of the intake valve when closed.
    Sulski Performance Tuning
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    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  14. #14
    Advanced Tuner Bluecat's Avatar
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    Quote Originally Posted by WS6FirebirdTA00 View Post
    The bigger problem I see here is the risk/reward. Later injection will insure you have less just passing through the exhaust but also runs the risk of washing the cylinders down. Too early and now you are passing even more though the exhaust, but can spray to the back of the intake valve when closed.
    That pretty much sums it up.

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    Quote Originally Posted by Bluecat View Post
    That pretty much sums it up.
    wouldnt that mean using the smallest injector that is safe to use for the power level?

    too low of a duty cycle and the risk of washing down the cylinders increases while too high means not getting the fuel needed into the cylinder. am i on the right track?

  16. #16
    Tuning Addict WS6FirebirdTA00's Avatar
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    So, please let me know if I am understanding.

    You are saying that at 300.5º after the peak of the compression stroke is the EOI. So in stock form, all injection is done before the intake valve even lifts? Am I confusing myself here?
    Sulski Performance Tuning
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    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

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    Quote Originally Posted by WS6FirebirdTA00 View Post
    So, please let me know if I am understanding.

    You are saying that at 300.5º after the peak of the compression stroke is the EOI. So in stock form, all injection is done before the intake valve even lifts? Am I confusing myself here?
    yes, the gm engineers set it up so the fuel would evaporate on the warm intake valve which lead to better fuel mixture/emissions/etc.

    my response in teh other thread lays it out. the idea is that each reference point in the timing tables is worth 90* of the total cycle:
    0-0
    1-90
    2-180
    3-270
    4-360
    5-450
    6-540
    7-630
    8-720

    with the formula he provides, it breaks it down in a way to be useful with the use of a cam card.
    Last edited by Wnts2Go10O; 01-07-2011 at 06:59 PM.

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    Senior Tuner S2H's Avatar
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    Never Mind.. the math just clicked in my head.....
    answered my own question
    Last edited by S2H; 01-12-2011 at 12:55 AM.
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    I was thinking....and you should be able to put the injection timing anywhere you want it....if 656 isn't late enough (8 Normal and 8 Boundary) then start thinking in terms of 2 engine cycles, ie 0 Normal and 0 Boundary should be the same as 4 Normal + 4 Boundary which should also equal 8 Normal and 8 Boundary.

    And here is why I think they did it:

    If your boundary + normal = 8 somewhere in your range, the interpolation wouldn't work if it was only 1 720* cycle.

    As for the -784, the first cycle is -64* (0 Boundary and 0 Normal), which is probably the first tooth the PCM calculates on a cycle (the earliest you can spark is -60, so this isn't far off from here).

  20. #20
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    Bringing it back from the dead! Very good thread. someone make a xls to calculate the EOIT for an inputed camshaft value

    -Carl