Troubleshooting Atomic EFI - misfire condition

Discussion in 'High Tech for Old Iron' started by gs_jimmy, Jun 27, 2018.

  1. gs_jimmy

    gs_jimmy Well-Known Member

    OK, I have the Atomic EFI on my 455 Stage 1 (all stock, with HEI). Over the last few times I have had it out it developed what felt like a misfire condition. So, I have all new: Cap, Rotor (MSD), Accel 8mm wires, plugs, radio suppression condenser. I ran all the wires to the HEI, under the cap and to the pick up. The module tested fine. I think we can eliminate that as the source.

    Next I had an O2 lead that shorted to the exhaust manifold. (that must be it?!?). Fixed and no change at all. The fuel system is set-up as "Returnless" single feed to the unit. My idle FP is 36-38lbs and idle speed is set to 720 rpm. The "squirt" is set to 19. The engine does fire right up and seems to idle OK. But as load is applied the car feels like it is breaking up in the ignition. At cruise speed 2400-2600 car seems fine.

    So any ideas from the group?

    I will be re-running the grounds at all points and adding a block ground to the frame. May need to seriously consider a return system using the Corvette regulator.
  2. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    I do not know how the software is set up, but I'd bet it needs more accel enrichment/pump shot. It's probably a lean stumble off idle and accelleration.
  3. gs_jimmy

    gs_jimmy Well-Known Member

    Finally had some time to work on the Buick after vacation this weekend. Had been thinking about the run condition and what it feels like. Had run the wiring on the EFI previously and also checked for kinks in the fuel line (nothing found). So I went at got a $10 ignition recurve kit and pulled the distributor apart. I found that both of the weight post plastic bushings were worn, making the weights sloppy. It was also curved for the 4 speed and not the TH400 it now runs.

    So I added the kit to the top of the distributor and took it out on a test drive. Now I can light up the tires no problem. But the is still a little bit of a misfire in the ignition. So after letting it cool down overnight, I went and ran all the plugs. I found that #3 & #5 are oil fouled. My thought is that over the winter there was a bit of build up in those 2 chambers that caused this condition. I'm really hoping that it isn't stuck oil rings allowing blow by. If that is the case, I'll try Top Engine cleaner and an EOS additive to the oil. Of course the alternative would be a compression check on 3 & 5 to see where I'm at, then a tear down for new rings. Engine only has maybe 20,000 on it and sees limited use.
  4. gs_jimmy

    gs_jimmy Well-Known Member

    FOUND IT: The mystery has been solved. I ran a compression check, #3 = 0 PSI, #5 = 0 PSI (ran it a couple times), then ran #1 = 125 PSI. So guess who is pulling an engine tonight? Really sux, but the issue isn't going to just "Go Away" on its own. The plan is to get the engine out tonight and on the stand. Got the hood off and top of the engine stripped off. Under car connections later today. This will also give me the chance to find/fix a trans leak that's been bugging me for a while now.

    Plan is to re-ring the engine and also new valve guide seals/relap the valves. No noises in the lower end, so the crank isn't coming out (I hope). Also a good time to swap out the flex plate (couple bad teeth). I'll take some pic's when the heads come off. Wish me luck
  5. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I'd pull that head before yanking the motor. You may have a bad head gasket or some bad valves. The short block could be fine.
  6. gs_jimmy

    gs_jimmy Well-Known Member

    Ok, engine is out, the crime scene has been cleaned up (trans oil all over the floor), trans is on the work table, engine bay has been degreased and readied for detailing. Now the million dollar question, what's wrong with the engine and why was it misfiring?

    I was able to tear into the engine before I quit for the night. Pulled the driver side head and was greeted with..............a blown head gasket. Actually blown out in 2 places, first was between the #3 & #5 cylinders, then above the number 5 into the intake valley (that would be why the crank case was pressurizing and pushing out oil).

    Took some PB Blaster and cleaned off the top of the pistons to check for damage (none found), then razor bladed the top deck and cylinder head to check on any damage there (looks good, but need to put a straight edge on it). I did note that the cylinders still have cross hatch in them, no scoring or scuffing found either! Cam lobes all look good (won't be disturbing the short block).

    So I'll be ordering the complete Fel-Pro gasket kit and replacing the valve stem seals/head gaskets. Will also be doing the oil pan to inspect for any other damage/leaks. And of course a good cleaning inside & out.

    So once everything is buttoned up I'll start the search for an OD trans. I'm leaning towards a TH700R4 from a Corvette or BBC application, then using an adapter plate. Right now I'm fighting a leak on the TH400 that I'm having a hard time finding. A rebuild OD would take care of that issue and give me a deeper 1st gear, and .70 OD feature. Currently running 3.31 rear gearing (Chevelle 12 bolt).
    Last edited: Aug 6, 2018
  7. gs_jimmy

    gs_jimmy Well-Known Member

    Head gasket

    Attached Files:

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