Pertronix Ignition Issue

Discussion in 'Sparky's corner' started by Bigpig455, May 19, 2015.

  1. Bigpig455

    Bigpig455 Fastest of the slow....

    I'm running a Ignitor III on my 73 Stage 1 car, and I've got a weak, erratic spark at idle.

    The car is set up like this: 24 degrees in the distributor at 2750, 12 initial, Flamethrower coil run with a dedicated 12v feed (bosch relay from the battery using the resistor wire as the trigger) - the coil is new, as I crushed the last one overtightening the bracket and screwed it up. Newish Bosch plugs with great color and no damage, gapped to 35 thou and NAPA Beldon wires with no significant resistance.

    I had to keep the ignition way advanced to run right, and so I thought I had a vacuum leak. But last weekend I blocked everything off and there was no vacuum leak. I also noticed it had alot of RPM drop as I put it in gear. So I check the idle, and it was around 1000 RPM. So I brought the initial back down from 20ish to 12, and it again ran crappy, barely idling but no rpm drop in gear and idled at about 600. Checked the spark line with a scope and it looked great (surprisingly).

    So I put a timing light on it to measure the advance at 1000 rpm (10 degrees) and noticed that when I brought the timing back to 12 initial and the idle dropped, the spark was erratic and weak. bring the rpms back up, and the spark strengthens and hits every stroke. Checked the coil voltage at low RPM - 14.2 v. I then took a spark thingee and put it inline with the wire/plug and was able to dial in the gap to 35 thou, and watched the spark at low and high idle - low idle its like brownish, thin and only fires like every other time, high idle it gets brighter and thicker, but never whitish or what I would consider full strength like on my 71 or 65 cars.

    All this time I thought I was covering for a vacuum leak, I was actually just advancing timing until the idle came up and restored some spark.

    So what could cause the weak erratic spark at low RPM if the coil has a steady 14.2 input voltage? Please note that even with this issue the car still runs strong - 14.2 @ 96 generally. I just couldn't idle w/ the AC on and the car ran about 210 in traffic.

    Interested in your opinion and follow up questions.

    Thanks,
     
  2. lapham3@aol.com

    lapham3@aol.com Well-Known Member

    Might try another known good coil-good luck
     
  3. Bigpig455

    Bigpig455 Fastest of the slow....

    Thanks Dan - I'll try that, also will try to test the one in the car before I go too far
     
  4. 66BulldogGS

    66BulldogGS Platinum Level Contributor

    The first thing to check with any electrical issue is your grounds. I would check your wires in the distributor. Make sure your wire ground in the distributor is good and make sure none of the wires are getting weak from flexing. Also check that the wires on the coil are tight. And it never hurts to check your ground at the battery and to the block. Weak grounds can cause some crazy stuff to happen. And try another coil like Dan said.
     
    Last edited: May 21, 2015
  5. telriv

    telriv Founders Club Member

    Is that the one we replaced the coil with another used one in your driveway????
     
  6. Wildcat GS

    Wildcat GS Wildcat GS

    Seems to me your problem could be supplied voltage at the coil because as you raise the rpm the system voltage is probably rising a little as compared to the voltage at idle speed (this may or may not be necessarily so depending on your alternator/regulater combo). I dont like the fact you are using a greatly reduced voltage source for a trigger to the relay which is supplying voltage to the coil. I know you stated voltage is over 14 (which sounds a little weird to me, I would expect high 13`s but that of course varies). Try using a jumper directly from the hot side of the battery to the hot side of the coil to see if your spark at idle improves. That should only take 5 minutes. Good luck! Always have been fond of your `73 since seeing it on Ebay.
    Tom Mooney
     
  7. Bigpig455

    Bigpig455 Fastest of the slow....

    Tom it is the car we out the coil in, it made it run strong on the road, but it never would idle well.

    Tom Mooney - thanks for the tip, I did actually run a jumper, no change in spark or idle. I did measure before and after voltage.14.2 at the battery and coil at idle. I rebuilt the alternator with a new "made in the USA" regulator, so I probably am responsible for that anomaly.

    And I'm flattered you remember the car, I'm not gonna lie -it's awesome. I have just been chipping away at it little by little, I haven't changed a thing visually. It's still got the sidepipes and huge whip antenna, like something out of a Burt Reynolds movie....

    Here are some pics from last year at LVD...

    DSC09780_4916.jpg
     

    Attached Files:

  8. Wildcat GS

    Wildcat GS Wildcat GS

    Awesome
    Tom
     
  9. Wildcat GS

    Wildcat GS Wildcat GS

    Rhett,
    Didnt realize this was a reference to a "pertronix" setup. Havnt had any exposure to this style of point substitute for years (last time I purchased such a kit they were calling it a "Perlux") but is there an air gap adjustment between the pickup and reluctor wheel? What shape are your dizzy bushings in? Just some random thoughts...
    Tom
     
  10. Bigpig455

    Bigpig455 Fastest of the slow....

    Tom - both great questions, and happy to tell you I know the answers..

    My old Corvair had the Pertronix set up where you had to set (and maintain) the reluctor gap, but these systems are located by the point plate screw holes, and built to a set gap tolerance with no adjustment..

    The bushings and end play were both checked out during the distributor rebuilds and were good.

    The question I really need to answer is engine grounding. Thats been stuck in my head, but unfortunatly I'm 1000 miles away from the car this week. I'll keep you all posted.
     
  11. telriv

    telriv Founders Club Member

    Si I guess that means NO DRAG RACING this week-end!!!!!
     
  12. Bigpig455

    Bigpig455 Fastest of the slow....

    I never said that!

    I'm headed up tomorrow with the 71! I was out of town all week, and hadn't had the chance to tell you that I mashed our two distributors together and scoped it, it's running better than ever.

    However, I probably wont get back to low spark issue on the 73 until next weekend.

    If you want to come by and grab the 65 on the way up, let me know! I've got no co-drivers as of yet.
     
  13. fireredstage1

    fireredstage1 Active Member

    I'm curious why you are using the resistance wire as the trigger from the relay? When I've installed these in my cars, I pull the resistance wire out of the junction block and repalce it with a regular wire. I then run that wire straight to the coil... This might be your issue.
     
  14. Bigpig455

    Bigpig455 Fastest of the slow....

    Hey all - finally got this car back down to ground level to work on it, and here's what I found:

    Voltage to the coil is 13.6 - 13.7 with a known good meter - I said 14.2 before , but that meter was junk.

    Coil tested good - 1.5 ohms resistance primary, 6k ohms secondary (I might have that backward)

    Engine is grounded at rest - less than 1.5 ohm resistance through the body and negative cable, each tested independently. with cable on and off.

    Jumper wire to positive coil makes no difference

    Jumper wire to negative battery and body ground makes no difference

    Jumper cable from battery to head bolt makes no difference

    The car does have the original "strap" ground from the engine to firewall, and it has continuity too.

    Here's where in gets weird:

    When the car is running, the resistance to negative battery jumps up to maybe 4-5 ohms, resistance to body ground probably 3-4 ohms.

    While the car was running choppy I had a meter on it, ground resistance to battery was jumping from 50 to 10 ohms, then all of a sudden the car smoothed out a little and it settled at 5 ohms again and the spark got brighter (but still not at what I see on the 65 and 71 cars) Glad I caught that transition on the meter.

    One more piece of information - I have a diode in the alternator pigtail so the car will shut off when you turn the key, without it the 12v ignition feed relay would backfeed the alternator with the key off but alternator still turning, and it had just enough voltage to keep the car running. The 71 and 65 don't do this.

    I'm psyched I'm finally on to the this car's problem, I spent a couple years chasing vacuum leaks, trying different carbs and distributors, etc..I'm close to getting this thing to finally run right, I can feel it!

    So my question is: what would cause a car's ground resistance to rise when running? Is this normal?

    Thanks again.
     
  15. telriv

    telriv Founders Club Member

    Rhett you NEED to learn how to do a voltage drop test!!!! This ohm thing could be throwing you off.
     
  16. jaystoy

    jaystoy Well-Known Member

    My .02, dump the pertronix. I have nothing but issues with the pertronix in my 71. I am running MSD box through points. Works flawless
     
  17. eagleguy

    eagleguy 1971 Skylark Custom

    Summit sells a HEI replacement distributor set up from Pro Form that even comes with a Buick red cap!
     
  18. Bigpig455

    Bigpig455 Fastest of the slow....

    Tommy!

    This what your talking about?

    http://www.aa1car.com/library/voltage_drop_testing.htm


    I'll try to give you a call tomorrow to discuss.

    Jay!

    I've had great luck with the Pertronix in the other two cars, and this issue came with the car. It was doing it when it had the Stinger S-4 in it too...thanks for weighing in though..
     
  19. telriv

    telriv Founders Club Member

    Yes, exactly Rhett.

    I won't be around tomorrow. Got a doctor's appt. & other things where I won't be home till at least 7pm.
     
  20. Daves72

    Daves72 I get jokes.

    I have a Pertronix III and Flamethrower III coil on mine. The first unit I received turned out to be defective. It's been several years ago but it was missing, if memory serves me. I called the Pertronix tech support number and they did some troubleshooting with me and ultimately replaced it with one they had pretested. This was back in 2009-10 I think.
     

Share This Page