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    Continuing Ignition Woes

    Now tearing my hair out and would really appreciate some advice on this one if anyone can help.

    For around 15 years, I had next to no ignition problems with twin points, and later Accuspark electronic unit, then I suddenly had hot starting problems.
    Since then I have replaced the rotor arm and cap twice (now running a LD green rotor arm and motor factor sourced Lucas cap, new HT leads, Pertronix Ignitor and have three coils. (A Blue Accuspark, Bosch red and Intermotor), all 6V.

    The car starts and runs fine initially, no hot starting issues. The misfire doesn't show until the car is thoroughly warm and has done 10 to 20 miles when the coil is hot. Starts as very slight misfire and gets worse over the next few miles to the point the car misfires under anything but the lightest throttle. Swap the coil for a cold spare and all is good for another 10 miles.

    Timing is ok and was set after replacing timing chains, ballast wire checked and 1.5 ohms between fuse 2 and the white/pink coil connection.
    There is around 7.1 ohms between coil -ve white/slate tacho coil wire (is this right?) and the 12V supply to the Pertronics is ok.
    Earth strap on the distributer plate ok, slight resistance (<0.3 ohms) between distributer plate and battery -ve

    When running at tickover, there is only around 2 Volts across the LV coil contacts measured with a DVM and 12V between coil +ve and earth. Is this correct?

    Wondering if the Pertronics is faulty, but these devices tend to either work or they don't. I could re-fit the accuspark but it is a bit of a rave.
    I don't see why I would need to run a 12V coil without ballast and believe that Pertronix advise against this anyway.

    Does anyone have any opinion if my coil is overheating for some reason or if the coil isn't seeing enough voltage across it for some reason causing a weak spark when the coil is hot, or where the fault may be? (it's definitely not fuel related).

    Thanks in advance, Mark.

    #2
    Sorry if I misunderstand your measurements but I hope this helps. I am assuming the ballast is still connected 'in circuit' with the correct 'ballast' coil. The ballast wire sounds OK at 1.5 ohms (assuming you took account of meter leads etc).
    Using a typical DMM for voltage measurements can be misleading. When the engine is running, and the coil is being switched, the voltage readings at the coil will be indeterminate because the digital meters cannot measure pulsing voltages and usually jump around. I dont know how you got a reading of 12V at coil + with engine running?

    To check if your ignition circuit is correct I recommend you:
    1. Put a temporary short of the coil NEG to ground (to establish conditions).
    2. Switch the ignition (briefly) on and measure the DC volts at the coil POS. This should be approx half battery voltage. So for a 12V battery reading you should get about 6 volts. +/- a volt. If you get about 9 volts it could mean your coil is a non-ballasted (12V) type. If you get battery volts it means your ballast is not in circuit. Remove the temp short! If you get about 4 volts you probably have a double ballast (this does happen!).

    If you have the wrong coil type for your circuit this may explain the cause of misfire. NB Bosch and Intermotor coils are usually reliable. Other makes may not be.
    Last edited by Wheelz; 3 October 2021, 17:49.
    Chris

    Comment


      #3
      Do the checks as Mr Wheelz says, then I would consider a failing ballast as it seems unlikely you have two duff coils, though it is possible, - that would explain why swapping coils only provides temporary relief as the ballast could be failing due to temperature as well. Is yours the resistance wire in the loom or the earlier separate resistor bolted to the coil? Either way worth checking it when hot. Don't rely on a plain resistance measurement, you need to check it under load, simply connect the temporary earth to the coil as per the instructions from Wheelz and measure the coil voltage - should be a healthy 6V ish. You may find if the ballast resistance is increasing with temperature and thus the voltage at the coil has dropped and is the reason for the weak spark/miss fire.

      Also don't assume that electronic ignition modules either work or don't, they are boxes of evil magic that can get temperamental especially when hot

      Roger
      White TV8 BW35 no mods and now a Dolly Sprint to keep it company
      So many cars, so little time!

      Comment


        #4
        I have had similar problems for a few years. Recently had a ballast resistor fail (Mk1 Stag with separate resistor, not in the loom), then the king lead failed, and shortly after that, the coil (Bosch Red) would power a test plug which was not in the engine, but fail to spark the plug in the pressurised cylinder charge in the engine (tested by having an old-fashioned timing light in circuit with the plug).
        It seemed that every time I identified a problem (and I have got through a few coils in the last few years), it would run fine for a while then something else would fail/
        I was running Accuspark, but I have also used a spare distributor with original twin points.
        I have reverted to a new Lumenition set (because at least you can do static tests on that), paired with their coil and ballast resistor, and new plug leads. So far so good, but not done many miles yet.
        Very frustrated that I cannot positively identify what was wrong.
        '72 Manual O/d Saffron Yellow

        Comment


          #5
          Had /a Bosch red fail this year. Replaced with a viper coil. All good.
          Hot start issues do seem to be on the increase with modern fuel low boiling point. (As low as 36 degrees!!!)
          check fuel pressure isn’t too high. 2.25psi seems ideal.
          Consider fitting a nylon fuel pipe from pump to filter & a silicone fibreglass shield.
          Consider fitting a back to tank restricted bypass.
          The bypass allows the relief of fuel pressure build up after a key off heat soak / fuel boiling & subsequent wet flooding.
          Use wide open throttle when hot start cranking .
          Wet flooding causes bore and piston ring damage.
          So it’s worth taking steps to prevent it.
          There are 2 secrets to staying on top :- 1. Don't give everything away.
          2.

          Comment


            #6
            Does the loom ballast resister fail? If it does,how so? Then what is the fix?


            Last edited by singapore stag; 4 October 2021, 04:36.

            Comment


              #7
              the Pertronix I have in my mk1 clearly says to remove ballast and use a 1.5 ohm coil. they do not recommend a 3 ohm coil. you mention you still have a ballast. I would use the Pertronix documentation and report back.

              Comment


                #8
                Originally posted by sujitroy View Post
                the Pertronix I have in my mk1 clearly says to remove ballast and use a 1.5 ohm coil. they do not recommend a 3 ohm coil. you mention you still have a ballast. I would use the Pertronix documentation and report back.
                Is that the Pertronix Ignitor II or I ? As I understand it, the Ignitor I is the basic fixed dwell angle type, which allows more coil current to flow an so reducing to 1.5 ohm will make the coil run much hotter? The ignitor II has variable dwell which has better control of coil current and allows low impedance coils to be used.
                Last edited by Wheelz; 4 October 2021, 08:48.
                Chris

                Comment


                  #9
                  I've checked the Pertronix installation instructions. It is an Ignitor (1) LU-181A
                  These state:
                  Minimum total primary resistance 1.5 ohms is necessary.
                  If your ignition system presently is equipped with a ballast resistor, do not remove it.

                  The system is installed as per fig.2 wiring diagram.

                  I bought the Pertronix unit because of their reputation for being reliable!

                  I did find this last night with a Midget having similar issues.

                  At the bottom, the importers suggested these units can be sensitive to poor earthing.

                  Voltages checked at coil, 12.2V supply, 5.7V at coil +ve when negative side earthed.
                  Primary coil resistance 1.6 ohms and 1.7 ohms for the red and Accuspark coils.
                  Zero ohms between the Pertronix unit mounting screw and block and -ve side of battery.
                  as already said, ballast wire checked at 1.5 ohms.

                  Where to next?

                  Points were a bit all over the place, dizzy has done 80k so bearings not the tightest, points pitting with failed condenser, new quality points and condenser would have cost more than the Accuspark and baseplate.

                  First thing is to check the voltages/resistances again when the car is misfiring, possibly by-pass the ballast wire and use an external ballast resistor.
                  If this doesn't uncover anything, I think I'll re-fit the Accuspark "cheap Chinese rubbish" that served me well for all those years.
                  I did have hot starting incidents when this unit was fitted. In fact when hot there were three times the car refused to start when hot with no signs of firing at all when cranking, once when the car had been stood 45 mins, once only 5 mins. When it did start it seemed to taks a while to "catch" then it would run ok when it did start. Was this fuel related? I don't know.
                  Thinking now that this was more likely down to an old black 15 year old rotor arm rather than the Accuspark, but who knows?

                  Thanks for all the help and suggestions so far. I'm determined to get to the bottom of this since I haven't really fully enjoyed the car for three years now due to one thing or another!

                  Comment


                    #10
                    I had an issue with my Pertonix 1, having the ignition on without engine running while doing something else
                    & cooked the coil.

                    Since then I re-jigged my imobiliser, so if just ign is turned on then no power is applied to the coil.
                    Now I run the Pertronix 1 into a Bosch Blue 3ohm coil this is non ballasted.
                    I ran a separate feed to bypass the original resistance wire, now goes through the immobiliser 1st.
                    No issues coil cooking / starting / misfiring in the last 2k miles at any temperature.

                    Comment


                      #11
                      Originally posted by NeilR View Post
                      I had an issue with my Pertonix 1, having the ignition on without engine running while doing something else
                      & cooked the coil.

                      Since then I re-jigged my imobiliser, so if just ign is turned on then no power is applied to the coil.
                      Now I run the Pertronix 1 into a Bosch Blue 3ohm coil this is non ballasted.
                      I ran a separate feed to bypass the original resistance wire, now goes through the immobiliser 1st.
                      No issues coil cooking / starting / misfiring in the last 2k miles at any temperature.
                      I think the Ignitor 2 is protected from this. I never leave the ignition on.
                      Unballasted coil is an option but shouldn't be required.

                      You may have a point about the immobiliser. I know mine protects two circuits and I used starter but will test to see if I immobilised the coil feed through this as well.

                      Comment


                        #12
                        I had two old Lucas coils fail. Similar issue - mis-firing when hot after about 140 minutes. Wait 10 minutes and then all good again. Swapped coils and the same thing. These were both 12V coils but with the ballast resistor still in circuit. I then powered direct from 12V - but same misfire. Changed accuspark for another and the same again. I read so much on here about coils going, that I eventually got a new Bosch blue coil (12V) and all is now fine. Ballast resistor is now also back in circuit.

                        Comment


                          #13
                          Originally posted by MikeParker View Post
                          I had two old Lucas coils fail. Similar issue - mis-firing when hot after about 140 minutes. Wait 10 minutes and then all good again. Swapped coils and the same thing. These were both 12V coils but with the ballast resistor still in circuit. I then powered direct from 12V - but same misfire. Changed accuspark for another and the same again. I read so much on here about coils going, that I eventually got a new Bosch blue coil (12V) and all is now fine. Ballast resistor is now also back in circuit.
                          This is how I ended up with the Bosch Red coil. Thought I'd cured it at first but no. I believe these are solid rather than oil filled?
                          I've run cars with coils for years and never had any problems or misfires like this, or had to replace a coil until the Stag.

                          Comment


                            #14
                            I too had multiple new HT coils that all stopped working when hot. Three IIRC. Bosch coil now works perfectly, but I take great care to keep it from touching the engine block.
                            Header tanks - you can't beat a bit of bling.

                            Comment


                              #15
                              Mark.
                              This doesn't really help any, but the ballast coil on my Stag has been there for at least 25 years, firstly with points and then two different electronic ignition systems. Clearly they were once made to last a long time, and we are in a bad situation if a properly reliable coil is now so difficult to find.
                              There must be tens of thousands of cars on the roads in the UK still using them. Are their owners having the same reliability problems that we seem to have? I don't see any reason why Stags should be a special case.
                              I wonder which make Peter at LDParts sells. He is always very particular about the quality of his components.
                              Mike.

                              Comment

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