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:

  8. gs_jimmy

    gs_jimmy Well-Known Member

    Almost done with the repair. Lots of detailing work, routing of wires, hoses and such. Have been waiting on the intake gasket to button it up, should be in today. Ran my compression test yesterday, all cylinders are at about 175 lbs. The exception is #5, at 150+. This is the one I had out to inspect. Should fully seat after start-up. After this is fired up, I will need to repair the battery side inner fender during the reassembly of the front clip. Hate to work so slowly, but time & funds are the limiting factors. IMG952018082795193608491.jpg IMG952018082795193618564.jpg

    Right now everything is in the chassis and hook-up's are taking place. More pic's to come
    sriley531 likes this.
  9. gs_jimmy

    gs_jimmy Well-Known Member

    GOT IT! So after all the farting around I was able to sort out my misfire, and get it running nice. Found that a couple wires were routed incorrectly. This was leading to the misfire returning. Got my timing set to 6* at the crank, now takes throttle like it should. Still need to put it on the ramps and double check the underside connections (really close now!).

    So after all of this I now find that the TB is trying to fire in the Key Off position with the Handheld staying "ON" (should be off/dark). Leads me to a couple thoughts:

    1. There is a dead short in my power wiring. The main wire is running through the firewall and attached at the fuse block. Not real likely, but you never know.

    2. An open connection in the steering column at the ignition switch. Seems more likely as there is no neutral safety switch hooked up at the trans. Can engage at the column by rotating the collar.

    3. A melted wire at the starter area allowing a power feed back.

    4. I did the 3 wire conversion on the internal regulated alternator. My handheld is showing an over charge situation 16-18 volts with random spikes. Really need some ideas here. Can't drive that way.

    This is that last "Bug in the system" that I need to run down. Right now the battery is disconnected to insure I'm not burning something down.

    Ideas here? I'll be pulling the wiring schematic now
  10. gs_jimmy

    gs_jimmy Well-Known Member

    Yesterday I found a ground wire disconnected, that fixed the random voltage spike at the hand held. But I'm still getting a backfire "thru the carb (TB)". A bit of research says to open the TB set screw about 1/16th inch to prevent the blades from slamming shut.

    The backfire seems to be a lean condition after acceleration (mid-range to WOT & back down). What I need to know is the basic parameters for setting up the system. Looks like I need to richen up the part throttle setting as the entire ignition is new. Super close to being able to really drive now.
    sriley531 likes this.
  11. gs_jimmy

    gs_jimmy Well-Known Member

    After more research into why an engine backfire through the carb (EFI in this case) It comes down to 2 issues, timing and vacuum (leaks). So right now I have timing at 6*, give or take. Will reverify this tonight.

    But after reading a 100 posts on the issue, I'm coming down to a vacuum leak. On the Buick's we run the PCV at the back of the carb, with the hose routed to the front. Everything I'm seeing would indicate that this is the source of the issue (I tried everything else). It could also be the base gasket at the manifold, I'll grab some carb cleaner on the way home to see if I pick up RPM by spraying the base area at the manifold/EFI TB.

    My thought on all of this is the un-metered air of a vacuum leak is giving the EFI controller/ECU an issue. That is what could be the cause of a backfire through the intake/EFI on decel. due to an over rich condition. (Yes the plugs are black). This may call for new plugs yet again.
  12. gs_jimmy

    gs_jimmy Well-Known Member

    GOT IT

    Timing was way off, no vacuum leaks. Reset from -2* to 8.5*, no more back fire, takes throttle fine. Will drive it tonight after work (and before the darn deer come out).
    TheSilverBuick likes this.

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