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Unsolvable problem on only one cylinder with Pertronix module

Discussion in '206/246' started by chritin, Sep 2, 2019.

  1. chritin

    chritin Rookie

    Jul 12, 2007
    10
    france
    Full Name:
    chritin regis
    Hello to all,

    I’ve an unsolvable problem with a model 9MR-161A on my Dino 246. It works well on 5 cylinders, but I've a lot of misfire on cylinder 1, and only on cylinder 1 on my engine. The exhaust pipe stay cold on this cylinder.

    I think everything has been checked, here ist he list:

    - Mounting of the Ignitor ans magnet sleeve strickly confom to installation guide

    - Impedance between ignitor plate and (-) battery measured lower then 0.2 ohm as Pertonix said to verify.

    - Voltage on (+) ignitor measured higher than 14.2 Volts, so it’s OK

    - Coil primary résistance 3 ohm and no ballast resistor (A second coil has been tested, same problem)

    - Ignition timing perfectly ajusted in static and dynamic with my strobe light

    - Compression on cylinder 1 verified and ok

    - Spark plug on cylinder one OK (Exchange with new spark but same problem)

    - Cable between disttributor head and spark tested (Exchange with new cable, same problem)

    - Igniter head new, and impedance on output for cylinder one tested and ok

    More than that, my distributor has been tested on a other Dino and works perfectly well. So the Ignitor module is OK. And this other Dino has exactly the same configuration with a Pertronix too, and works very well .

    I become crazy with this problem ... ! I can’t explain why it happens only on one cylinder compared to everything that was controlled.

    Any idea of anything else to test more than on the list above ? Or any experience with a similar problem ?

    Thanks

    Régis
     
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  3. 4CamGT

    4CamGT Formula 3

    Jun 23, 2004
    2,374
    Southern California
    1) Have you tried running the motor with the ignition lead disconnected from the spark plug and checking if it is sparking? 2) Is fuel filling the cylinder? 3) What about the carburetor throat? Each cylinder has one throat. Clogged jet?
     
  4. TonyL

    TonyL F1 Rookie
    Silver Subscribed

    Sep 27, 2007
    2,992
    UK
    Full Name:
    Tony
    Try cleaning out the idle jet as 4camgt suggests, clean out circuit with comp. air then try the air mixture screw. Start 2 turns out then slowly wind in / or out to see when the cylinder comes back. You will hear a distinct shift in revs when it does. If you wind in the MS all the way in so it bottoms out and still get no response out then -
    Operate the throttle opening and see if fuel squirts from the pump jet inside the venturi
    Also make sure air by pass screw is about 1/4 turn open to closed. To far open and this will drastically weaken the fuel mix. If you fiddle with these then its best to check all the air flows through each barrel as well so you don't upset the balance.
    Tony
     
  5. Ken Ivey

    Ken Ivey Karting
    Silver Subscribed

    Jan 6, 2013
    129
    Portland, OR, USA
    Full Name:
    Ken Ivey
    Start with 4camgt's suggestion on checking for spark. The units aren't always good. I ran one for many years in a different car with great success - but tried to put one on my Dino and gave up - I have a Luminition unit now...
     
  6. chritin

    chritin Rookie

    Jul 12, 2007
    10
    france
    Full Name:
    chritin regis
    Thanks for your answers. In fact the fuel arrives, the spark plug is wet but I saw with an external spark plug that there is no one spark per turn, and at very low revs no spark at all. As if the ignitor wouldn't trigger on each turn. I need to invastigate because the same distributor installed on an other car works perfectly well and the coil voltage is 14,2 V on the two cars. Very strange ...
     
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  8. Fred Winterburn

    Fred Winterburn Karting

    Jan 27, 2015
    68
    Perhaps move the magnet ring and see if the problem moves to another cylinder. Fred
     
  9. TonyL

    TonyL F1 Rookie
    Silver Subscribed

    Sep 27, 2007
    2,992
    UK
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    Tony
    to much fuel - you say in your opening post that the spark plug is OK ! Now you say it is wet fouled?

    Seems like you have investigated most if not all ignition causes so before you dismiss the carb, check the accelerator pump jet is not operating at idle

    check and verify that the air flows to each barrel are exactly the same, to much airflow through cylinder 1 can indicate the throttle plate is too far open, allowing excess fuel to spill through the progression port /s

    Check mixture settings

    Check float levels and shut off valve work OK, if it doesn't fuel can spill over

    Was it working OK then the fault suddenly appeared or have you changed anything?

    Tony
     
  10. chritin

    chritin Rookie

    Jul 12, 2007
    10
    france
    Full Name:
    chritin regis
    Yes I said the spark plug is ok because with another and new one the problem is the same. It's not due to a faulty spark plug.
    Moving the magnet sleeve is a good idea Fred
     
  11. dgt

    dgt Formula 3
    Silver Subscribed Owner

    Jan 14, 2011
    1,210
    Northeast, USA & Oz
    Full Name:
    Andrew
    No fuel... it’s likely air isn’t being sucked through the carb, check for leaks in the hoses around the booster vacuum hose which connects to the into cylinder 1 under the carb in the inlet manifold. Only cylinder 1 can suffer this.
    Tighten all the clamps back to the booster, a loose clamp will cause this condition where air bypasses the carb.

    Quick test, pull the vacuum hose off and block the hole to see if it runs properly.
     
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  13. synchro

    synchro F1 Veteran

    Feb 14, 2005
    9,211
    CHNDLR
    Full Name:
    Scott
    #10 synchro, Sep 8, 2019
    Last edited: Sep 8, 2019
    Pertronix must be impedance matched or risk failure, it is on their website (althougvh you did mention yours had met the minimum 3 Ohms req).

    Why not add an MSD box to that?
    The Pertronix MR-11211 ignitor is rated for use by MSD 6421 as a standard input. i.e don't use the Pertronix as an ignitor but as a trigger to the MSD which easily fits inside a Marelli AEC-103 box. This allows modern function and OEM look - alike.... plus you don't have funky coil impedance to match which risks pertronix failure.

    Wiring diagram:

    http://www.manualsdir.com/manuals/256548/22/msd-6421-6al-2-ignition-control-installation-page22.png
     
  14. chritin

    chritin Rookie

    Jul 12, 2007
    10
    france
    Full Name:
    chritin regis
    Thanks for your answers, now I think the ignition is not the problem. I tried it manually outside of the car on a battery and have a nice spark on all the 6 spark plug. I will investigate on the carburettor and the idle jet soon ...
     
  15. chritin

    chritin Rookie

    Jul 12, 2007
    10
    france
    Full Name:
    chritin regis
    Problem solved ! The idle jet was loosened on the carburetor for the cylindre not working normally, nothing more. The effect is very suprising !
     
    dgt, cls and TonyL like this.
  16. 4CamGT

    4CamGT Formula 3

    Jun 23, 2004
    2,374
    Southern California
    I’m really happy to hear you solved it! It must make you feel great that you found the problem and it was so small! Nothing worse than chasing an intermittent gremlin! I put my original DCNF’s back on my car and I really made sure everything was tight and took special attention to all the vacuum lines. It’s never ran so well! These cars vibrate and it’s always a good idea to check tightness, rubber cracks etc. Even perfectly restored examples can break down because of a parts failure!
     

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