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Old 07-28-2010, 06:36 PM
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Looking for info on selecting an Ignition Coil

After a lot of troubleshooting for a misfire in my Ford 428, I have found out that when I run dual-points in my Mallory Distributor, everything is fine, but when I use my Pertronix Ignitor module in place of the points, the engine misfires once really warmed up (and on a hot day).

Of course when I say everything is fine with points, that not quite true. The engine doesn't run quite so smoothly, but at least it doesn't fall flat on its face with disconcerting bangs like it does with the Pertronix Unit.

I've checked the dwell, and with the points, my coil is drawing current for about 35 degrees of dist revolution and with the Pertronix, it's about 25 degrees. (I havn't hooked the scope up yet with the Pertronix, but am going on what the Pertronix Tech rep tells me....I will be checking it out though).

Seems my spark is so weak with the Pertronix, it can't handle acceleration when everything is hot.

As the Pertronix unit doesn't actually fail, I started looking at my ignition coil wondering if it properly matched for the Pertronix Unit.

It is a Napa (Echlin) IC12. My spare coil is a cheaper IC14SB, more or less the same thing.

Looking at the Pertronix site (a page I can't seem to find again), it states that their FlameThrower coil comes in two types. The one with a 3 ohm primary is for 4 or 6 cylinder engines and they recommend a 1.5 ohm primary for 8 cylinder engines. This tells me a lower primary resistance is needed for an 8 cylinder where the dwell time is half that of a four cylinder, so more current must be drawn over a shorter period in order to get sufficient energy into the coil.

So I think I will order a 1.5 ohm Flamethrower coil and try it. Fairly cheap, so it's not a big deal.

There is some confusion though:

1/ Pertronix says there Ignitor 1 can handle 8 amps and that you can use their 1.5 ohm Flamethrower coil without a ballast resistor (good as I'm not using a ballast resistor now), however that calculation is made using V= IxR where V=12 volts, and of course 12 = 8 x 1.5. However, with a running engine, the supply voltage is closer to 14 volts so perhaps a 0.2 or 0.3 ohm ballast resistor might increase the Pertronix Unit life expectancy.

2/ A lot of people seem to think that a 3 ohm coil is normal and a 1.5 ohm coil needs a 1.5 ohm ballast resistor. I think this is true for 4 cylinder cars and of course most of my research that led to this involved MGAs and other small sports cars, etc. (4 cylinder cars).

So here's my situation. I have two Mallory dual point distributors and two Pertronix Ignitor units, so I would like to keep using these parts vs getting a whole new MSD set-up. Additionally, I would like to keep my car looking period correct, so a big finned MSD box in the engine bay isn't quite my style.

Can anyone confirm all my theorizing above and additionally, can anyone recommend a really good coil as an alternative to the Pertronix Flamethrower?

Thank-you.

EDIT: Here's the module/coil application chart I had trouble finding:

http://www.pertronix.com/prod/ig/flame/coils/chart.aspx

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Last edited by Argess; 07-28-2010 at 07:40 PM.
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Old 07-28-2010, 08:28 PM
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I have to admit to having no first hand knowledge or Pertronix ignitions but their advertising has always seemed a bit hokey. That is too good to be true - I use MSD as it has been proven everywhere. Mallory has gone the Accel/Mr Gasket route and they are not what they used to be in years past.

OK, now that you've heard my preferences , let's do a tune up on that car. With dual points, the individual gaps should be .019-.021 and individual point dwell angles are 25 with a combined dwell of 33-36 degrees. Initial timing is at least 8 degrees at 500 rpm. Before crappy unleaded gas, and using Sunoco 260, I would set mine at 10-12 BTDC. You do need a ballast resistor unless Pertronix/Mallory says leave it off. You do need a good condenser and the coil needs to be connected polarity wise correctly. As far as a replacement, I do like MSD products but a NAPA (Eichlin or Standard brand will work just fine)

Spark plugs are probably Autolite BF32 or better yet, Champions F11Y or F14Y
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Old 07-28-2010, 08:34 PM
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Quote:
Originally Posted by Argess
After a lot of troubleshooting for a misfire in my Ford 428, I have found out that when I run dual-points in my Mallory Distributor, everything is fine, but when I use my Pertronix Ignitor module in place of the points, the engine misfires once really warmed up (and on a hot day).

Of course when I say everything is fine with points, that not quite true. The engine doesn't run quite so smoothly, but at least it doesn't fall flat on its face with disconcerting bangs like it does with the Pertronix Unit.

I've checked the dwell, and with the points, my coil is drawing current for about 35 degrees of dist revolution and with the Pertronix, it's about 25 degrees. (I havn't hooked the scope up yet with the Pertronix, but am going on what the Pertronix Tech rep tells me....I will be checking it out though).

Seems my spark is so weak with the Pertronix, it can't handle acceleration when everything is hot.

As the Pertronix unit doesn't actually fail, I started looking at my ignition coil wondering if it properly matched for the Pertronix Unit.

It is a Napa (Echlin) IC12. My spare coil is a cheaper IC14SB, more or less the same thing.

Looking at the Pertronix site (a page I can't seem to find again), it states that their FlameThrower coil comes in two types. The one with a 3 ohm primary is for 4 or 6 cylinder engines and they recommend a 1.5 ohm primary for 8 cylinder engines. This tells me a lower primary resistance is needed for an 8 cylinder where the dwell time is half that of a four cylinder, so more current must be drawn over a shorter period in order to get sufficient energy into the coil.

So I think I will order a 1.5 ohm Flamethrower coil and try it. Fairly cheap, so it's not a big deal.

There is some confusion though:

1/ Pertronix says there Ignitor 1 can handle 8 amps and that you can use their 1.5 ohm Flamethrower coil without a ballast resistor (good as I'm not using a ballast resistor now), however that calculation is made using V= IxR where V=12 volts, and of course 12 = 8 x 1.5. However, with a running engine, the supply voltage is closer to 14 volts so perhaps a 0.2 or 0.3 ohm ballast resistor might increase the Pertronix Unit life expectancy.

2/ A lot of people seem to think that a 3 ohm coil is normal and a 1.5 ohm coil needs a 1.5 ohm ballast resistor. I think this is true for 4 cylinder cars and of course most of my research that led to this involved MGAs and other small sports cars, etc. (4 cylinder cars).

So here's my situation. I have two Mallory dual point distributors and two Pertronix Ignitor units, so I would like to keep using these parts vs getting a whole new MSD set-up. Additionally, I would like to keep my car looking period correct, so a big finned MSD box in the engine bay isn't quite my style.

Can anyone confirm all my theorizing above and additionally, can anyone recommend a really good coil as an alternative to the Pertronix Flamethrower?

Thank-you.

EDIT: Here's the module/coil application chart I had trouble finding:

http://www.pertronix.com/prod/ig/flame/coils/chart.aspx

Your math looks good.Not to sure about the pertronic units. I saw this website and it had a lot to offer.

HTTP://autoxer.skiblack.com/rayignition.html

I read it twice. Maybe it can help.
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Old 07-29-2010, 06:19 AM
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Thanks guys. Good link too.

It's difficult to find much on igntion component selection. Most information either talks about troubleshooting a system that used to work OK, or talks about a complete upgrade, such as MSD.

My system did work fine before the rebuild. The change seems to be that my compression is now higher. Having the block deck and cyl heads resurfaced has contributed. An over bore has contributed. This is indicated by my cranking pressure which is up 10 to 15 psi from before. So it would appear my igntion was barely adequate before, and now it's not.

I'm going to re-install the Pertronix Unit today and connect the scope to see the difference between it and the points when it comes to dwell and spark duration, etc. I'm also off to the store to get a lower primary resistance coil....the Flamethrower recommended by Pertronix for my Ignitor module. They probably have to order it, but I'll return with my findings in case others can benifit from my attempts to throw money at the problem until it goes away...LOL.
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Old 07-29-2010, 10:49 AM
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On the opposite side of the Pertronix unit supplying a weak current, there's a chance that it's supplying enough more current than the points to cause the plug wires to cross fire. Or the cap to arc across to another terminal due to a carbon track.

A simple spark plug test w/a plug removed from the engine, grounded while the engine is momentarily cranked will show you what kind of spark you're getting at the plug gap. Or use one of those simple testers w/the adjustable gap. If the Pertronix unit shows a big, blue snappy arc, that may be what's happening.

But in any event, that you say "disconcerting bangs" is VERY worrisome to me- it says that there is an occasional BAD occurrence of crossfiring or some sort of ignition-induced detonation of a type that could be very harmful- as in breaking ring lands, hammering bearings, even damage to the crank could occur.
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Old 07-29-2010, 11:19 AM
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Quote:
Originally Posted by cobalt327
On the opposite side of the Pertronix unit supplying a weak current, there's a chance that it's supplying enough more current than the points to cause the plug wires to cross fire. Or the cap to arc across to another terminal due to a carbon track.

A simple spark plug test w/a plug removed from the engine, grounded while the engine is momentarily cranked will show you what kind of spark you're getting at the plug gap. Or use one of those simple testers w/the adjustable gap. If the Pertronix unit shows a big, blue snappy arc, that may be what's happening.

But in any event, that you say "disconcerting bangs" is VERY worrisome to me- it says that there is an occasional BAD occurrence of crossfiring or some sort of ignition-induced detonation of a type that could be very harmful- as in breaking ring lands, hammering bearings, even damage to the crank could occur.
On the disconcerting bang, it's unburnt fuel igniting in the sidepipes. The fuel doesn't get ignited in the cylinders (due to a misfire) and goes out with the exhaust. A slight air leak between the primary headers and the sidepipe collectors allows a bit of air in and hence the "bang".

Last year, I did have some bangs coming from the engine, not the exhaust. They were bad. Can't believe the engine held up through them. I'm sure it was crossfire. New plug wires cured that, although I suspected dist cap issues at the time. No carbon tracking, plus I had a spare cap that made no difference.

I did do a spark check...last year...with one of those little adjustable gap things. It all looked good, although I don't remember details. The problem is that those testers will show a high voltage being present, but really offer no clue as to spark duration, and hence energy. As you say, all you can do is look at it and see if it's bright, blue and fat. I was setting my rough timing statically, and I use a grounded sparkplug connected the the coil output to know where the Pertronix Unit or points open. Spark does look thin and weak at that time, but I wasn't paying a lot of attention to it.

But you make a good point. It could be a better spark with the Pertronix is finding an easier path to ground than across the sparkplug when the cylinder pressure and temp are high. I have done a midnight test, and there's no signs of spark leaks, but the engine isn't under any sort of load then....just idling. Not sure how to perform a more quantitative test on the spark itself.

I've ordered the Pertronix coil...only $30. If that doesn't fix the problem, I'll have to do more testing of one kind or another.

Thank-you for your input. I appreciate it. If I get no-where with the new coil, all the suggestions and thought should help me figure this thing out. Two heads are better than one, and with these internet forums, there's lots of heads out there.
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Old 07-29-2010, 11:38 AM
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I'm much relieved to hear that the bangs are of a sort that won't take your engine out, and it seems you are really on top of this deal. Hopefully the lower resistance coil will be the ticket- I'll cross my fingers for ya'! lol
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Old 07-29-2010, 11:48 AM
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Thanks for the vote of confidence. Usually I work things out myself, but this whole issue has been a frustrating one, and I can use the calm of third party advice (the first two parties being me and the engine...LOL). For a while, I was thinking it was carb related. I've been in every different direction, but sticking with it is narrowing things down. I sure hope I can report back with some real positive information concluding with a final success.
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Old 07-29-2010, 08:13 PM
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Im starting to think the pertronics cant handle the electrical load demanded by ANY coil when high rpm and heat come into play especially with the new compression ratio involved. I realize its what you have and the reluctance to part with hard earned samolians is a good incentive to make it work. I know a lot of Modules arent designed for high rpm as the cuircutry is not built for high speed switching as required. Heat really can play a big part too as you probably know heat affects magnetism in an adverse way it weakens its effect . The pertronics is a reluctor type setup I believe, yes, no ? anyway I think heat is taking its toll or a least pushing its capability of the unit to its edge as heat is weakening the effect of the signal generated by the reluctor/pickup coil part of the system.The only other thingI can think of would be distributor bushing wear. but I am leaning torwards the pertronics as switching on and of time is only certain on the dual point system where as with the pertronics unit you will need a digital storage oscilliscope to verify on off times and you will need to have it hooked up at the proper point in the circutry and replicate the condition could be a pretty daunting task.I could be in space with all of this but its a hunch. If you think heat could be a factor maybe some dry Ice around the distributor at the right time ( when symptoms occur) would squelch it long enough to confirm the theory or put it to bed.I guess it would eliminate one thing if anything. I dont want to sound like a know it all, just wanted to share my thoughts ,maybe it will lead you in the right direction ...or give you a good laugh.
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Old 07-30-2010, 07:00 AM
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OK, lets say the Pertronix unit doesn't have the huevos to kick a spark under severe conditions. What detrimental effect would this cause if the Pertronix unit was used as a switch for an aftermarket ignition amp?

Does everyone think it might not be good for even that? Just thinking of a way to get some use out of the Per. unit, is all.
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Old 07-30-2010, 07:53 AM
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pertronix

u NEED to make sure u have the resistance in the ign sys or u will burn out the pertronix sys... been there !!!!! if u have a ballast resistor make sure of the ohms. replacing coils is no biggie but keep in mind of the total ohms needed by manuf.
i cooked mine and went to mallory and like it better..
but bottom line is the total resistance. if your close to zero or less then one ohm, make sure u have a trl handy...
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Old 07-30-2010, 02:08 PM
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Well.....I've finsihed my testing and although their is support for my insufficient dwell theory and hence the need for a lower resistance primary coil, there is also some spark quality testing that favours the Pertronix Unit. So I remain confused.

First of all I did a spark gap test using a variable gap spark plug tester. Here are the results:

1/ Points installed, spark would only jump 1/4" (in air) and looked thin and weak. (Points wern`t in the best condition and engine does run slightly rough with them)

2/ Pertronix installed, spark would jump 7/16" (in air) and looked very strong.

Idle Test at 750 rpm:

Dwell time with the points: 35.4 degrees, coil ringing 9 degrees

Dwell time with Pertronix: 26.4 degrees, spark generation 4 degrees

According to Pertronix, the magnet sleeve you install over the dist shaft should have the lower edge level with the Ignitor Module (Hall Effect sensor inside module). In mine, it is slightly low. I removed the Pertronix supplied spacer that goes between the magnet sleeve and the rotor button and moved the sleeve up so the magnets aligned better. The dwell increased from 26.4 degrees to 38.25 degrees.

This means I have to test drive the car again in hot weather.

Sidenote: By the way, if it is too much spark vs not enough, and the spark is causing crossfire as it`s arcing somewhere, say inside the dist cap, I`m not sure how to confirm that or fix it. I have no room for a larger dist cap distributor.

Here`s some pics that might help clarify what I am trying to say above. The scope graphs were done by hand and arn`t 100% accurate. Should have tried to photograph the scope screen. The first pic is to show you what the Pertronix Points replacement kit looks like. The rivets are highlighted as at one time I was suspecting them of causing a bad connection.





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Old 07-30-2010, 03:12 PM
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After seeing the diagrahm of the alignment of the magnet it is clear to me that is most likeley your problem. In such a small target area alignment is critical not so much with an old school ford hei where the blades of the trigger wheel have like 1/2 an inch or more to aim for. With such a critical target area it makes perfect sense as the field of magnetic lines would not be aligned in the most effective area. they would tend to be skewed being so close to the plate as well and in extreme conditions woud be weak and innefective .I would at this point actually bet money on your latest repair.I am not a gambling man either.Like i said heat effects magnetism by weakening the effect.It makes too perfect of sense to not be the case.Hope it works.

Last edited by latech; 07-30-2010 at 03:20 PM.
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Old 07-30-2010, 03:32 PM
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Yes, I`m very encouraged by seeing the significant increase in dwell when I aligned the magents and the sensor. I have to make an internal spacer now to make sure the magnet sleeve doesn`t drop down to where it was.

Still not sure if it`s not enough spark, or too much. I did have some crossfire bangs last year, but thought new plug wires fixed it. If it is crossfire in the distributor, I could grind away a bit of the leading edge of the rotor button tip....i.e. make the gap between the rotor tip and the next dist cap contact further apart....or heaven forbid, add ballast to reduce the spark to somewhere between what points give me and what the Pertronix Unit gives me.....not my favourite idea.

I did check phasing, and when the crank is set exactly half way between my intial and max timings, the rotor points exactly towards no. 1 plug wire terminal. So it would be a little closer to the next adjacent terminal at max mechanical advance.

More test driving to come, but it is a cooler day today and the problem only happenes when its very hot out. For me this is one big headache, but someday this thread may help someone else out.
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Old 07-30-2010, 03:45 PM
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I wonder if they make a rotor with "Horse Blinders" on the sides of the tip or at least the leading edge. Cutting part of it away would seem like the easiest and probably very affective way to accomplish this to achieve the same results
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