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Thread: Need help with fuel managment.

  1. #11

    Default Need help with fuel managment.

    Just remember to disconnect the vacuum advance when you check/set your base timing, otherwise you will be reading combined base+vac adv.

  2. #12

    Default Need help with fuel managment.

    JWZ28 wrote:

    Darn good article. I understood before hand but it does explain why vac advance is necessary. The Street Fire distributor I'm running has a restrictor plate so I can manage the amount of advance it adds, so I'll try it when I reprogram the system for my current setup



    Since you liked that article, try googling "Lars vacuum Advance".

    (Lars Grimsrud has written a few other papers also)

    You want to find out the manifold vacuum of your car at idle. Your vacuum advance should be fully deployed at two inches less vacuum than what you have at idle. I would limit your vacuum advance to somewhere between ten to fourteen degrees.

    Gerry

  3. #13

    Default Need help with fuel managment.

    My distributor is the adjustable one so I can restrict the amount of advance it adds. I should be in good shape. Thanks for the help. I'll post up as soon as I get a chance to try it out.



  4. #14

    Default Need help with fuel managment.

    Ok I performed a reset, reset the throttle blades, cleared diagnostics, and hooked up full manifold advance (limited to 8-11*).



    Started the engine and let it get up to operating temp. Adjusted the throttle blades evenly to achieve idle within 100rpm of my target idle (700rpm). Let the engine run for at least ten minutes. Checked timing and it's at 23* at idle (at operating temp) with the full manifold vac hooked up.



    For the first bit the temp was spiking up over 210, but would drop after blipping the throttle. I took it for a short drive when it got dark and let it idle again after pulling back in the garage. I did notice some popping from the exhaust on deceleration, but I'm assuming that's normal while the system learns? The temp seemed to get better, only creeping to 200 before dropping back down and keeping a pretty good hold (no overheating).



    I also checked the headers in the dark and the glow seems to be gone. The exhaust was burning my eyes as well, which is a good sign to me that it's getting a more than healthy dose of fuel now.



    It did try to die a few times when I'd come to a stop, but I remember it doing that when I first bought the system, and assume it will cure itself with some drive time. Any input on that would be much appreciated. Thanks for the help.

  5. #15

    Default Need help with fuel managment.

    You might try some more vacuum advance. If you get surging at cruising speeds, then you have gone too far.

    Before you change the vacuum advance, record the injector duty cycle at idle in the Atomic's dashboard. It will probably read five percent or so. See if it goes down after adding more advance. If it does, it means the engine is running more efficiently, and maybe a bit cooler.

    Stoichiometric for ethanol blends is about 14.1:1, ethanol free gas is about 14.7:1. I run my idle afr at about 14.3, and cruise afr at around 14.5. At idle it doesn't burn my eyes.

    Popping from the exhaust on decel is usually an exhaust leak.

    Good luck!

    Gerry

  6. #16

    Default Need help with fuel managment.

    Gotcha. If it's an exhaust leak then it's after the collector, because I'm not receiving any error codes. I'll drive it some more and see how things go.. Right now the IAC is reading 0, but the instructions say not to worry about that right now, so I guess it's normal for the first bit of driving.

  7. #17

    Default Need help with fuel managment.

    I am curious about your statement "Adjusted the throttle blades evenly to achieve idle within 100rpm of my target idle (700rpm)". Why would you do this?

    The IAC will adjust for idle RPM. You should be setting IAC with the throttle blade adjustment and letting the computer do the target seeking.

  8. #18

    Default Need help with fuel managment.

    fcsallan wrote:
    I am curious about your statement "Adjusted the throttle blades evenly to achieve idle within 100rpm of my target idle (700rpm)". Why would you do this?

    The IAC will adjust for idle RPM. You should be setting IAC with the throttle blade adjustment and letting the computer do the target seeking.

    This is correct. While it's OK to have it at zero, it should just barely be there.

    Also, with regards to the popping out the exhaust on decel, have you retorqed the header bolts after the head swap? I believe the Atomic shuts off the injectors on deceleration until you get down to about two thousand rpm. You shouldn't have any popping when the injectors are turned off.

    Gerry

  9. #19

    Default Need help with fuel managment.

    On the comprehensive reset page, it says to adjust the throttle blades evenly a 1/4 turn at a time to get within 100rpm of target idle.



    I treated it like a new out of the box initial startup. Set to performance cam, 355ci, 8 cylinders, 750 target idle, set throttle blades 1 1/2 turns out from the closed position, and fired the engine. It ran at 2,000rpm for a good bit, and once it warmed up I adjusted the throttle blades evenly until my idle was at about 800 rpm.



    Should I have let it come down from 2,000rpm all on it's own? IAC dropped to about 19ish when it got warm while I ran it today.



    As for the headers, yes I've been re-torquing them after the first few heat cycles.

  10. #20

    Default Need help with fuel managment.

    JWZ28 wrote:

    On the comprehensive reset page, it says to adjust the throttle blades evenly a 1/4 turn at a time to get within 100rpm of target idle.



    I treated it like a new out of the box initial startup. Set to performance cam, 355ci, 8 cylinders, 750 target idle, set throttle blades 1 1/2 turns out from the closed position, and fired the engine. It ran at 2,000rpm for a good bit, and once it warmed up I adjusted the throttle blades evenly until my idle was at about 800 rpm.



    Should I have let it come down from 2,000rpm all on it's own? IAC dropped to about 19ish when it got warm while I ran it today.



    As for the headers, yes I retorqued them and they're as tight as they'll go, but I can hear them leaking somewhere. I've cut in between the flanges to get a better seal, but that seal may have been compromised when the headers were glowing hot.

    If it started and ran at 2000 rpm for a good bit, the throttle plates were probably already

    opened up too much, and it wouldn't have come down on its own. If your IAC is at 19 at warm idle, you are fine.

    What I meant earlier is that while driving, if you are decelerating, (think going down a steep hill and using the engine to slow you down instead of the brakes) the injectors will be off until you slow down enough that the rpm gets to 2000rpm. There is no need for fuel then. Below 2000 the injectors are working again.

    Gerry

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