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Thread: Olds 455 Atomic Efi Settings

  1. #1

    Default Olds 455 Atomic Efi Settings

    Just putting the finishing touches on an Atomic install on my 72 Cutl**** car specs below. The car is mostly a cruiser, it sees a little strip time but overall I am looking for it to run good for cruising. I have setup the dist as per the instructions, locked out with 84211 rotor phasing set 15 retarded. I will be able to turn the key in the next few days.

    The question is what to use for initial setup / timing specs?

    Car specs are:

    1971 Olds 455 & TH400

    KB 277 15cc dish 30 over pistons (comp around 9.8:1)

    Erson Cam 298/306 (232/240 @ 0.050) on a 110 with .568 lift on both

    Comp Cam Roller Rockers / Pushrods / PBM Hydraulic Lifters

    Olds Large Valve 2.07/1.71 G Heads / Mild Porting

    Edelbrock Performer 2151 intake

    Hooker Comp non-tuned Headers 3902 / 3 inch Pypes dual exhaust

    MSD Pro-Billet Dist 8566 & Mallory Hyfire 6AL

    Caprice Fuel tank with in-tank pump & Fuel Regulator

  2. #2

    Default Olds 455 Atomic Efi Settings

    Well got the car running on the Atomic efi, overall it went pretty smoothly. I was able to take the car for a drive and so far I am very happy with the drivability and throttle response, the car seems to have a ton more acceleration from a stop.

    I am however experiencing two issues, cold starting & the idle RPM (in park). When I initially set the IAC, by eyeballing it before starting the car, the car fired up but it was idling at about 2,500 rpm. I backed off both screws about 3/4 of a turn and got is down into the 900 range when in park when warm. This is ok however I notice the rpm seems to bounce around from 800-1,000 and I would like to get it down closer to 800 when in park but the only way to do that is to further back out the IAC screws. The trouble is this seems to affect the cold startup, when I tried to start it cold today it took about 6 or so seconds of cranking to get it going, is this normal or should it fire sooner?

    The IAC count is 0, I wanted to see how close it was, I found by turning the screws 1/2 turn it changed to 1 while running, with the engine warm in park. I estimate they are currently set about at 1/2 turn open. The timing curve is good, I verified it with my gun and it is similar to my previous HEI setup, A/F Ratio is also good and fuel pressure is a steady 53psi. I also updated al 3 firmware two days ago so they are the most up to date version.

    Initial Setup:

    Camshaft Type Mild

    Fuel Pump Type Non-PWM Return

    Idle RPM Target 700

    Ignition Timing Settings:

    Idle RPM 1,000

    Total RPM 2,500

    Idle Adv 8.0

    Total Adv 35.0

    Vacuum Adv 6.0

    Vacuum Type Unported

  3. #3

    Default Olds 455 Atomic Efi Settings

    Two things I see is that you need to adjust the IAC by the directions in the manual. They must be adjusted equally and per the instructions.

    The other thing is that Idle RPM is set to 1,000, you should set it 100 above target idle rpm so should be 800.

    What are your A/F settings?

  4. #4

    Default Olds 455 Atomic Efi Settings

    Thanks for the reply, both IAC screws have always been adjusted equally like the process described in the manual.

    I did try moving the Idle RPM to 800 and 900 but that did not change much, it only advanced the timing a little more at idle as I suspect it moves the timing curve. I did not try this on a cold start though so that could help perhaps.

    I have left the A/F settings as is, which is

    Idle 14

    Cruise 14

    WOT 12.8

    Should I change the A/F settings, if so what should I try?

  5. #5

    Default Olds 455 Atomic Efi Settings

    What is your IAC cnt when warmed and in drive now? The system tries to use timing and the IAC to hit the idle rpm target. A/F ratios should be ok.

    BTW you should probably raise the Idle target to 800 and Idle to 900. Usually a bigger cam requires a higher idle rpm.

  6. #6

    Default Olds 455 Atomic Efi Settings

    IAC count is always 0, with the engine cold or warm, if in park or in drive both are also 0 IAC. If I turn both carb screws 1/2 turn in then the IAC comes up to 1, but the actual RPM then is also at 2,500.

    I will try 800 Idle Target and 900 Idle before starting it next and see if that helps with the initial starting and report back.

    I appreciate the advice!!

  7. #7

    Default Olds 455 Atomic Efi Settings

    Try closing each blade by 1/8 turn each (CCW) and see what your cnt does. It doesn't take much to adjust the idle and a 1/2 turn in might be too much, just a thought.

  8. #8

    Default Olds 455 Atomic Efi Settings

    Sounds good I can try closing them too, if I recall the rpms dropped when I did that last so my thought was it would stall out but I will try and see.

    One other thing:

    I did notice that when I turn the key to
    on, before starting when the engine was warm the IAC cnt said 65, thinking that
    maybe it opens the throttle a little for startup? This was when the car
    was already warm was just testing hot restart which seemed good. It would start, rpm would be about 1,200 then it would drop down to around 800 and idle and the IAC cnt would drop to 0.

    It almost seems that the blades are too closed when I go to start it cold but it could also have to do with the timing too. What sort of advance should I see on the handheld for starting, currently I am around 5-6 at idle and starting, then it goes up around 8 when in gear.

  9. #9

    Default Olds 455 Atomic Efi Settings

    I know that its normal for the idle to be high when you first start but it will come down to target in a few seconds. Not sure on this but with the blades closed some at start it's like a choke and then the system uses timing and the IAC to hit your target rpm.

    You should see around the 8* +/- 1* if everything is adjusted correctly and idle would vary about 50 rpm.

  10. #10

    Default Olds 455 Atomic Efi Settings

    I also just read that the IAC cnt decreases as you turn the throttle screws clockwise, I had that part backwards thinking the IAC cnt goes up as you open the throttle blades.

    Lots of new stuff to try here.

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