Idle RPM misfire

Discussion in ''Da Nailhead' started by Fragzem, Aug 8, 2020.

  1. Fragzem

    Fragzem Well-Known Member

    So I had this brilliant idea of "that ignition coil is 50 years old, let's change it". - Worked fine. Just had to change it.

    I used a new NGK coil and Delco Condenser (I guess that's just a radio suppressor bolted to the coil?)... hooked everything up the same way, and misfire at low RPM. If you get her to about 2000rpm, no misfires.

    Thought perhaps I've got a bad coil or something so I threw the original Delco coil back on. Same problem.

    What could've happened? This car was running perfect beforehand. I've checked all the other wires and cables and grounds. I can't have the coil wired backwards, could I? The condenser and distributor wire were together originally, and the red power wire was by itself.. and I'm pretty sure the red goes + and the dist/conden go -

    On top of this, I been trying to do it in my garage and I'm in the process of suffocating myself with the fumes... so it's been an interesting morning.
  2. gsgtx

    gsgtx Silver Level contributor

    coil wire itself from pulling on it ? run it without the condenser for the heck of it
  3. Fragzem

    Fragzem Well-Known Member

    Thank you. I keep feeling like this is it but the coil wire looks perfect... but looks aren't everything. I used some good dielectric grease when I put the wires on last year and it pulled off rather easily. But it's not impossible. I thought I saved my old coil wire - apparently not. I'm going to try another. (I did try without condenser with the "new" coil before I put the old back on - same thing)

    I just changed out the points for a new set. I thought it was a new set. Wouldn't run at all. Put old points back on and it fired right up, albeit back at square one with a nasty misfire. It's "whole-car-shaking-misfire" as it were this morning.

    I only have a few vacuum hoses. The brake booster - looks fine. The vac advance - fine. The PCV valve - old but fine....

    I cut the terminal off the red wire to the coil and put a new eyelet style connection on that just in case. Old one was holding on by a few strands so I'm glad I did that.
    Somebody spliced the wire from distributor to points together with a butt-connector in the middle at some point... but I'm assuming this is fine since the car runs at all. I'll get some proper spade-fork connectors and run an entire new wire for that soon.

    Cap/rotor are new from last year. Brass stuff, no aluminum.

    Plugs are new from this year. (actually using Bosch platinum (rockauto sale for $1) and they've run amazing until I messed with this coil)

    Last year I had the firing order mixed up. Triple-checked that. Good to go. It almost feels the same as when I had the firing order screwy. I didn't move wires around tho. Just the coil wire and maybe the #7 and #5 cyl.

    Checked the dwell, it's sitting right at 29-30.

    Honestly, up until this morning, the car has been running better than it has in 5 years. (I had a small rental with no garage and it got neglected in storage for a while).

    I hope its not some stupid coincidence like the fuel pump going bad. That's about the only thing I haven't touched on the car in 12 years of owning it.
    Last edited: Aug 8, 2020
  4. bostoncat68

    bostoncat68 Platinum Level Contributor

    I feel your pain -- I tell people these cars are like your first high school crush...the more attention you pay to them, the more they scorn you. Somedays you can't seem to win.

    It's a skip and you were messing with the ignition so you have to believe the simple answer (it's ignition related) is the answer. I think you need to pull the plug wires one at a time to see if you can isolate the misfire?? I would check & recheck your firing order if you moved any wires. Any chance you could have disturbed any plug wires such that you could have an arc somewhere ??). I think I might also really inspect the cap (did you reseat any wires -- could it have cracked???)

    Good luck. Sometimes a cold beverage and a night's sleep is required for a fresh perspective.
  5. Wildcat GS

    Wildcat GS Wildcat GS

    Is it backfiring? Try the ignition condensor
  6. gsjohnny1

    gsjohnny1 Well-Known Member

    check the unit that has the battery cables connection on the fenderwell for corrosion. had a 65 gs like that. couldn't figure out the skip.
  7. Fragzem

    Fragzem Well-Known Member

    Thank you all for the suggestions.

    I changed the distributor cap. Seems a tiny bit better. Dunno why - replaced new cap with older cap... but regardless - better.

    Began pulling plug wires. Started on the driver side, #6 and #8 seem to not be firing... got over to the other side and broke #3 while using my special cant-break-the-wires-tool. Go figure.

    Well, I guess it's a start. New wires, cap and rotor on the way. I guess I'm done futzing around until that all gets delivered.

    I also ordered a Pertronix 1181LS to replace the points. I have mixed feelings about it but I think I'll give them a try. Seem easy enough to switch back to points if I need.

    Tom - no backfiring. Will replace with old condenser anyway just to see.
  8. Stevem

    Stevem Well-Known Member

    The points wire that runs under the breaker plate on old Dizzy's has been known to have its insulation partially or fully dry rot off and make for intermittent cut outs / misses to flat out no spark conditions .

    If you had removed any plug wires be sure to double check your firing order as it's possible to have them wrong and get a bad miss, yet no back fire out the Carb.
  9. 322bnh

    322bnh Well-Known Member

    I chased a similar problem: missing and hard starting. Checked spark at plug and seemed weak, tried plug for spark on lawn mower, weak spark. Tried the mower plug, fat spark. Put in a set of Autolite 85 and instant start and smooth. Later I learned to never use "exotic" plugs with a carbureted engine; if fouled they do not recover like copper plugs. (the plugs were Bosch platinum)
  10. Gene Brink

    Gene Brink Active Member

    With 20/20 hindsight, and as a couple of previous posters, check to be certain your wires are going to the proper cylinder when the rotor is pointing at each cylinder. I mixed two up in 1964 (and am still pained by doing so) and had an excellent spark - so good it jumped to the piston top and burnt a hole in the piston top in less than 3 miles of driving. Huge clouds of white smoke and a less than 40k engine in need of a rebuild (a great experience but one I could have done without until my first MG which really needed a rebuild). Good luck on resolving.
  11. Schurkey

    Schurkey Silver Level contributor

    That's not right.

    There's two "condensers" (capacitators). One is in the distributor, it's purpose is to increase the service life of the points by reducing the arc when the points open. It's wired to the points, which in turn are connected to the coil. If you trace the wire from distributor to coil, it's connected to the - terminal.

    The other "condenser" is connected directly to the coil. It's intended to suppress radio static. THAT one goes to the + terminal.

    One condenser on each side of the coil. One on +, one on -.

    Sounds to me like you've got them both on the - terminal.
  12. Fragzem

    Fragzem Well-Known Member

    That's what I thought but it was backwards the last 12 years I guess. Thank you for reiterating that.

    I left that condenser off altogether and put new wires, cap, rotor...... no difference in how I'm running.

    I have an appointment at a local shop for the motor mounts tomorrow..... at one point, motor mounts was my only problem. LOL. I guess I'll be changing the appointment to let them fix this.... timing issue (I suppose it is). Aggravating because the car should be so simple and I've not solved this yet. I'm gonna see if I can get on the crankshaft bolt and be 100% sure the rotor is pointing to the correct #1 spot at TDC.
  13. Fragzem

    Fragzem Well-Known Member

    So.... she sure runs a lot better warm. I can actually shift to D and not stall...

    but I turned the crank to TDC a few times, checked it 4x... the #1 wire is indeed at #1 on the cap...
    for the first time in my life I've remembered a firing order in my head (I'm 36). 12784563... checked that 16 times.

    sprayed all around the engine and vac lines to look for a change in idle or a vacuum problem, didn't find anything.

    put that on-coil-condenser to the positive line just because. (i don't even have a speaker connected to my radio lol)

    changed out 2 plugs that had a little oil on them (6 and 8).. put in some old AC 44s I had laying here. Minor difference if any.

    It's going to be such a stupid thing when they figure this out Thursday. Just have that feeling. (changed appointment mentioned above to Thursday). At least the mechanic isn't a ripoff.
    I'll leave them with extra points, condensers, caps, rotors, coils and spark plugs and they can have at it I guess.
  14. Max Damage

    Max Damage Well-Known Member

    I am waiting to find us what this was? Please end the suspense...

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