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My PerTronix Digital HP electronic ignition has been great up till now - suddenly, the RPM signal to the electronic tachometer jumps 10-15 RPM for a second while the engine bucks with a misfire. This happens only occasionally, but if it's during a heavy load, I get a backfire.

I'm thinking my old breaker point feed to the firing signal is the issue - and I'll be cleaning the contacts on the points, but I'm wondering if others have had similar issues?

Maybe I should look into a magnetic pickup signal - no contacts to wear or dirty...

(This is on my 1976 Spider)
 

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Discussion Starter #2
Magnetic pickup??

Cleaning up the breaker points seems to have cured the issue (for now) - but the new engine has only been in and running for about 8 months!! Dust mixed with oil seems to be the issue - along with not enough current draw to spark-clean the contacts (signal usage draws very little current).

I'd like to avoid needing to maintain the old breaker points - so does anyone know of a drop-in magnetic pickup that's reliable?? Either in the dizzy or added to the front of the engine?
 

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I have had good luck with Pertronix kits in Bosch distributors. But your '76 probably has a Marelli. Others on the BB have reported finding a Pertronix model that will fit an Alfa Marelli distributor - you might do a search to find this thread or try calling Pertronix.

[ My guess is that the Pertronix application chart doesn't include Marelli distributors. edit: I stand corrected on this. If you enter "Marelli S103BA" into the Ignitor Kit Lookup page on the Pertronix site, it does return the two part numbers given in Bruce's post #8. ]
 

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Discussion Starter #5
I have had good luck with Pertronix kits in Bosch distributors. But your '76 probably has a Marelli. Others on the BB have reported finding a Pertronix model that will fit an Alfa Marelli distributor - you might do a search to find this thread or try calling Pertronix. My guess is that the Pertronix application chart doesn't include Marelli distributors.
Thanks to you and Alfar7 - I'll verify which distributor I have (it's a 1979 vintage engine - and modified from the original) and check out PerTronix's offerings... I like the PerTronix ignition box so far.
 

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Discussion Starter #6
Hmmm...

ZERO markings on the outside or inside of the distributor - is there a an ID photo of either one around?
 

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Discussion Starter #8
For others looking - it appears I have a Marelli S103BA distributor, and a PerTronix Ignitor 12V negative Ground MR-LS1 or Ignitor 2 9MR-LS1 can function as a contact-less trigger for the Digital HP model.

The MR-LS1 currently runs about $95, and the 9MR-LS1 is about $30-$40 more. For triggering the Digital HP, I'm thinking the cheaper one should be fine...
 

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My issue with these modules is that it is hard to tell if they are working properly. I helped a driver with his Alfa race car at Watkins Glen last year and we suspected ignition but it was hard to tell what was going on. We swapped one out but he was unsure of the rating. Some need a higher resistance coil and some work with with energy coils. I like the 123 distributor for many reasons, one being the LED that indicates the status of the solid state switch.
 

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Discussion Starter #10
My issue with these modules is that it is hard to tell if they are working properly. I helped a driver with his Alfa race car at Watkins Glen last year and we suspected ignition but it was hard to tell what was going on. We swapped one out but he was unsure of the rating. Some need a higher resistance coil and some work with with energy coils. I like the 123 distributor for many reasons, one being the LED that indicates the status of the solid state switch.
I kinda wondered about using one of those for a straight replacement of a breaker point -> coil. For my application, it is just feeding a signal to the Digital HP with it's diagnostic output to a yellow LED in my dash (none that really apply, though), and the Digital HP feeds the electronic tachometer too (which is how I diagnosed my point contact issue).

Those little modules don't offer any extra features, either - like redline cutout or multispark.
 

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Multispark is a marketing ploy to distract you from the fact that CD sparks have less energy than inductive sparks at low to mid rpms. They also mess up your timing light with sparks that are too late to make significant power. What some modules offer is variable dwell angle which allows the use of a low impedance coil and extends the full dwell time to higher rpm. GM HEI (Marelliplex), Bosch (L-Jet), 123 and maybe the top of the line Pertronix module have it.
 

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Discussion Starter #12
Multispark is a marketing ploy to distract you from the fact that CD sparks have less energy than inductive sparks at low to mid rpms. They also mess up your timing light with sparks that are too late to make significant power. What some modules offer is variable dwell angle which allows the use of a low impedance coil and extends the full dwell time to higher rpm. GM HEI (Marelliplex), Bosch (L-Jet), 123 and maybe the top of the line Pertronix module have it.
Looking at documentation, the spark energy they advertise is really a sum of the multiple spark energies - which, as you say, is not at all the same as a nice single high-energy spark. At best, it allows a second chance to fire - late by a bit. I may hook up a scope and see what their repeat rate is...

That electronic dwell extension would be the hot ticket. Something to look for when this ignition fails... IGBT's are common now that easily handle the current needed for a low impedance coil.
 

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That electronic dwell extension would be the hot ticket. Something to look for when this ignition fails... IGBT's are common now that easily handle the current needed for a low impedance coil.
Heat dissipation in the coil is a limiting factor at low to mid rpm. All of the inductive systems that I know about limit current to about 6 amps. There is not much to be gained by going lower than about 0.6 ohms/5 mH.
 

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The MR-LS1 currently runs about $95, and the 9MR-LS1 is about $30-$40 more. For triggering the Digital HP, I'm thinking the cheaper one should be fine...

Actually, it isn't. The version II is a much more electronically robust unit. If I were running a Pertronix (which I'm not) I'd use a II or III. The cost difference overall is minimal.
 

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GM HEI (Marelliplex), Bosch (L-Jet), 123 and maybe the top of the line Pertronix module have it.
[/QUOTE]


123 ignitions now allow the use of low impedance coils? Am I correct that the original versions used higher impedance coils? This is a real improvement.
 

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123 works with 1 ohm or more. I use my original type 123 with a 0.6 ohm/6 mH Blaster coil with a 0.6 ohm ballast resistor. maximum current is controlled at 6 amps which is similar to Bosch modules that I have tested and a little more than GM HEI. As I have explained in other threads, ability to connect to a lower resistance coil is of little advantage when the ignition limits the current. Without current limit a 1 ohm coil would draw 12 to 13 amps and the coil would burn up quickly. A 2 ohm coil would pull 6 to 6.5 amps. At low to medium rpm a 2 ohm coil will perform similarly to a 1 ohm or a 0.6 ohm with an ignition that limits current to 6 amps. I have seen claims that some modules will allow more than 6 amps but I am skeptical as they would make the coil run hotter.
So avoid the mistake of ranking ignitions by the lowest resistance coil to which they can be connected.
When used with a variable dwell, current limiting ignition a lower impedance coil will produce stronger sparks at high rpm but up to a point. Higher inductance increases to total energy that can be stored but it also slows the charging rate. Using a ballast resistor with a lower resistance coil is a good way to make stronger sparks. That has been known for decades.
 

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Looking at documentation, the spark energy they advertise is really a sum of the multiple spark energies - which, as you say, is not at all the same as a nice single high-energy spark. At best, it allows a second chance to fire - late by a bit. I may hook up a scope and see what their repeat rate is...

The advertised spark energy of 187mJ is the energy in just 1 spark, not a spark sequence. Some other boxes claim 1200+mJ/sequence, those are the ones that are the sum of several sparks. But the first spark of each sequence on the Digital HP is 187mJ. The repeat rate on most other brands boxes is about one every 1.1millisecond, which is why they stop multisparking at around 3000 RPM. The Digital HP is closer to 0.5millisecond repeat rate, which is why it multisparks to a much higher RPM, and the second spark timing is not as delayed as others.

This 187mJ is stronger than most inductive(dwell controlled) ignitions, even at low RPM. Multispark is to make up for the lower duration of the spark usually, not lower energy. Multispark is useful at light load, or lean mixtures, or similar situations. Basically, a molecule of fuel may not be in the spark gap at the right time to light off the combustion. Under full throttle acceleration, there is usually more fuel there so it isn't a problem, and the high energy lights it off.

You could always shut off the multispark on the Digital HP if you wanted to see how much of a difference it makes in performance, or if you wanted to shut it off when using a timing light. It should not be necessary to do it when using a timing light though, the light should always trigger on the first spark. People often notice smoother idle, light throttle cruise, starting, with the multispark on.

That electronic dwell extension would be the hot ticket. Something to look for when this ignition fails... IGBT's are common now that easily handle the current needed for a low impedance coil.
Dwell control is a huge improvement over a standard fixed dwell system, but the CDI is still usually able to light off a stronger spark at higher RPM because of how it delivers all of the energy so quickly.
 

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Discussion Starter #19
The advertised spark energy of 187mJ is the energy in just 1 spark, not a spark sequence. Some other boxes claim 1200+mJ/sequence, those are the ones that are the sum of several sparks. But the first spark of each sequence on the Digital HP is 187mJ. The repeat rate on most other brands boxes is about one every 1.1millisecond, which is why they stop multisparking at around 3000 RPM. The Digital HP is closer to 0.5millisecond repeat rate, which is why it multisparks to a much higher RPM, and the second spark timing is not as delayed as others.

This 187mJ is stronger than most inductive(dwell controlled) ignitions, even at low RPM. Multispark is to make up for the lower duration of the spark usually, not lower energy. Multispark is useful at light load, or lean mixtures, or similar situations. Basically, a molecule of fuel may not be in the spark gap at the right time to light off the combustion. Under full throttle acceleration, there is usually more fuel there so it isn't a problem, and the high energy lights it off.

You could always shut off the multispark on the Digital HP if you wanted to see how much of a difference it makes in performance, or if you wanted to shut it off when using a timing light. It should not be necessary to do it when using a timing light though, the light should always trigger on the first spark. People often notice smoother idle, light throttle cruise, starting, with the multispark on.



Dwell control is a huge improvement over a standard fixed dwell system, but the CDI is still usually able to light off a stronger spark at higher RPM because of how it delivers all of the energy so quickly.
All interesting info - are you associated with PerTronix, by chance??

Overcoming a coil's initial non-conducting impedance (that resistance to starting current flow) while keeping the voltage below an insulation breakdown point would seem like a limit on how fast you could multispark…
 

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All interesting info - are you associated with PerTronix, by chance??

Overcoming a coil's initial non-conducting impedance (that resistance to starting current flow) while keeping the voltage below an insulation breakdown point would seem like a limit on how fast you could multispark…
Yes, I designed the box.

The multispark rate limit is determined largely by the DC-DC converter circuit. On a CDI, to multispark you have to recharge the firing capacitor. To get 100 milliJoule charge in 1millisecond takes roughly a 100 Watt power supply. 1 Watt = 1 joule/second. Doubling the energy or halving the time, will double the wattage requirement of the power supply.
 
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