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Thread: Commanded Fuel when Cranking

  1. #11
    Joe (Moderator) joecar's Avatar
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    29° spark timing at high load seems too much (but I see you're running E85 even tho you have not edited B3601)... do you see/hear any spark knock...?

  2. #12
    Member O1Z06's Avatar
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    Not too long ago I got a new engine up and running and the startup is a pain in the buns. Here is what I did. First, that cranking EQ table does some very strange things based on other linked table influences. I said the heck with logging it and used IBPW instead. This gives a much better representation of what is going on. Also, logging with the V2 instead of the V7.5 scan during startup where everything happens quickly will help insure you don't drop or loose frames. Are you logging WB and is it on during cranking or is it switched of ignition which cycles when you crank?

    Regarding which tables to work, I would download a LQ9 LS1B truck .tun from the repository. I used this as a reference and it got me close but because I have a big cam and bigger engine, I had to keep adding some here and there. Set the cranking EQ table, cranking VE, initial fuel, first fuel pulse and after start to LQ9 tune. The cranking VE made the biggest difference. With my setup, I have a A1000 FPR and twin intank pumps. So there are no check valves and the system does not have full pressure until about a 1/2 second after you turn the key. Do you still have a check valve? The reason I ask is because the first fuel pulse B3204 has a timer then dumps an appropriate mass unit of fuel. If you watch IBPW you will see a spike where this happens. You have it at 3 seconds. Mine is at 14 ref pulses. Also, I don't use the second pulse, just added first and second into the first pulse. I don't even use the initial prime, just dump it all in the first pulse. The initial may help you though as it would dump fuel before you crank, allowed more time for the stingy alcohol to evaporate.

    When the temps get cold, alcohol doesn't have good volatility like gasoline does. The refinery tries to aid this by changing the blend slightly during winter. So with the LQ9 tune being for a larger engine, it may be all you need. But, if your still having issues, you might be able to increase the injection timing or EOIT. Taking out %20 from B3702 might help and let the fuel evaporate a bit longer, I don't know how much of an effect this will be on start up but I know it does make a difference once running especially with my cam. Hope this helps.
    Last edited by O1Z06; January 7th, 2013 at 09:31 AM.
    2001 Z06 512K Road Runner COS5
    LSx 427, Comp 7075 TT in progress

  3. #13
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    joecar,
    The only knock issues i have had was with burst knock when i would stab the throttle. I zero'd out the burst knock tables and haven't had an issue. I believe I changed the high spark table based on someones reference on here when they were tuning e85. I also didn't change b3601 because to tune for the e85 I did it the lazy way, but changing the fuel injector flow table instead. I tried the correct method of changing b3601 and all the tables to run e85 and it was a tuning nightmare starting from scratch. Also I live at high elevation so might also be why i get away with more timing.

    I think i'm gonna go change b5910 Spark ECT Table, so it adds a few more degree's of timing when ect are low.

    01Z06, thank you for the help. I will go look at doing some of that stuff. I was thinking that changine the VE while cranking table is where i need to look to add more fuel when starting. I'm wondering if this second fuel prime isn't what is causing me confusion.

    My issues is i turn the key on and let it sit till i hear the fuel pump turn off, and know the system is up to pressure. Then I will crank and crank on it, and the engine will not start. I won't turn the key off and let it sit a second or two then try cranking again, and it will fire up almost immediately! So there must be some sort of fuel prime happening on that second crank that is why it is firing.

    I will go add more fuel to the first initial prime and hope that helps. Also would it be good to shorten the time from 3 seconds down to 1? that way it is giving it more fuel immediately?

  4. #14
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    01Z06,

    I think using the lq9 files should help. Just comparing them the commanded fuel when cranking table seems to make much more since. Also the other tables are a tad richer. I have copied the tables over and will give this a try tonight.

    Thank you both for the help, I will let you know if it helped.

  5. #15
    Member O1Z06's Avatar
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    Increase the pulse delay to 14. We're talking milli seconds here. The difference between 3 and 1 is negligible. Make sure to take a log of startup with the V2 BBX and log IBPW PID.
    2001 Z06 512K Road Runner COS5
    LSx 427, Comp 7075 TT in progress

  6. #16
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    I'm confused, if it is milliseconds why would going from 3 to 14 make much of a difference? Less time for the alcohol to evaporate????

    thanks again for the help.

  7. #17
    Joe (Moderator) joecar's Avatar
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    More time for the fuel puddle to form on the port wall (so the dynamic wall wetting model could get going)...?

  8. #18
    Member O1Z06's Avatar
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    Using 150 rpm cranking, 1 ref pulse is .016 seconds, 3 ref pulses is .05 seconds, 14 ref pulses is .233 seconds and so on. During the batch fire pulse, the PCM looks at the mass of fuel requested and injector flow. After this pulse, it goes back to crank ve and cmd afr. You have scaled injectors? You would have to scale ve and pulse mass as well.
    2001 Z06 512K Road Runner COS5
    LSx 427, Comp 7075 TT in progress

  9. #19
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    Any update on this? I'm having this same issue. Perfect starts on gasoline, but cold starts on E85 takes 2 cranks and sometimes it struggles to idle for a couple seconds after startup.

  10. #20
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by GMCtrk View Post
    Any update on this? I'm having this same issue. Perfect starts on gasoline, but cold starts on E85 takes 2 cranks and sometimes it struggles to idle for a couple seconds after startup.
    What is your B3601 set to...?

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