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Thread: Olds 455 Atomic Efi Settings

  1. #21

    Default Olds 455 Atomic Efi Settings

    Good news got the misfire solved by running a ground directly to the battery for both the ignition box and atomic ecu. Previously I had them grounded to the firewall.

    Also did a little work on the trans governor, previously it was shifting around 3,700 now it's closer to 5,200. Also bumped the initial from 8 to 10 degrees, and adjusted the iac slightly it is now in the 0-20 range while in gear at a standstill.

    I took a drive this morning down a back road, car is running really well, tons of power I cannot launch with a full pedal or it just cooks the tires up to the top end of 2nd gear! Of course this is with cold street tires on a regular paved road... But still a hell of a lot of fun.

    I tried to drive at a few different speeds to get an idea of the a/f ration at different rpm, all looked to be in the 12-14 range so looks good.

    Three things I did notice:

    -the a/f reading every 30 seconds or so went to "warm up" even though I had been cruising for 20-30 minutes already. It would come back in a few seconds but could this be an o2 sensor starting to fail?

    -when the car is hot it starts ok, but not as good as when cold, it usually takes a few seconds longer of cranking then it partly fires but I almost have to give it some pedal

    -when taking off from a stop, the car is not as responsive as I think it could be, I need to give it more pedal then it finally takes off, not sure if this can be adjusted?

  2. #22

    Default Olds 455 Atomic Efi Settings


  3. #23

    Default Olds 455 Atomic Efi Settings

    Have a new problem to get some help with. Went for a drive tonight, car started up good as it normally does, drove for about 5 mins until it was all warmed up, ran good, then went out on the freeway to open it up and it bogged down on full throttle.

    This has not happened before, so I had my son with me, I had him watch the fuel pressure, a/f ratio and other specs to see what was going on. What we found was the a/f ratio was jumping up to the 18-20 range when I floored the pedal. Remember how it was previously showing "warm up" and error sometimes, so I am thinking that the o2 sensor might be going bad, I ordered a new one Bosch 17018 so we will see if this fixes up the issues.

    I had never seen it get over 14 or 15 previously and the fuel pressure was staying in the 48-54 range so I am thinking that is ok or is it low? Thank you

  4. #24

    Default Olds 455 Atomic Efi Settings

    18-20 shows real lean. The fuel pressure was good? Also check for exhaust leaks. A header leak will do this. Too much air getting to the O2 sensor and the Atomic will try to dump a ton of fuel in to compensate causing a bog.

  5. #25

    Default Olds 455 Atomic Efi Settings

    Yes the fuel pressure was good it was steady in the 48-54psi range. I put the car on the hoist today, checked for exhaust leaks, the header and flange gaskets all looked good. Should have the new o2 sensor in this week so we'll see how it does once that is installed.

    Anything else I should check over that could cause it to be lean?

  6. #26


    Well...funny story

    I was working on the car, started thinking about what could cause it to go lean other than the items suggested above, so I decided to pull the fuel pickup/pump as I have a caprice tank in my cutlass and its easy to get to via the trunk. When I looked inside I discovered that I was pretty much out of gas, so my sender/gauge is not accurate as it showed almost half a tank! hahaha

    Sometimes its the simplest things that can cause you problems. So lesson learned always make sure you have enough gas!!!

    I also put in the new O2 sensor after, car seems to run really well now so possible issues with the sensor that I hopefully resolved too.

  7. #27


    Two questions:

    -I am still having a little trouble with hot restarts, the car seems to start perfectly when cold, cranks for maybe 2 seconds then fires right up. When hot if I turn off and try to restart in 1 minute or up to about 1 hour after it seems to crank for about 5 seconds before it kicks, then it roughly starts and finally comes to life. Could the IAC affect this?

    -I am planning to dyno the car in the next month, I want to see what its making for power and I can also try some different settings if its worth it. Thinking I will stick with the cam setting at Mild, but maybe move the timing a little and also the A/F targets once I get some data from the dyno. Any advice on where to focus here as this is my first EFI dyno tune attempt.

    Thanks again

  8. #28


    Where is your IAC in gear with a warm engine now? I have found very minor adjustment to the IAC could alleviate the hot start issue, but those issues in my experience were mostly hard start when hot, not longer start. Does it labor to crank when it's hot or just takes a few more seconds?

  9. #29


    The IAC when warm in drive is zero, I was thinking I can try to get it closer to the 5-15 range. To do this do I need to loosen or tighten the 2 IAC screws? I believe it would be tighten right the throttle blades need to open slightly more?

    I have a hi-torque mini starter, it seems to turn the engine over good when hot and cold, the engine just doesn't seem to start as well when hot. It takes a few more seconds of cranking and when it does finally kick it does not idle instantly, it partly starts then after a few more seconds finally gets going smooth and up to idle.

    I will try to adjust the IAC and report back. Thanks again

  10. #30


    correct, open the blades a bit. evenly, front to back.

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