Waste-Spark-System problem ??

There was recent discussion over at the "stationary engine" forum. I'm looking to expand it here where more might read and give input.

Generally speaking (if I've got it correct) a waste-spark-system uses one controlled input at the primary coil winding, but the secondaries have both ends of the secondary coil hooked to two spark plugs. I've got a Shaw tractor with a 2-banger TE Wisonsin engine that uses this system. Also a French car (Deux Chevaux AKA 2CV). Also an Onan garden-tractor engine and also a 1973 Honda motorcycle.

Waste-spark makes a spark on both spark plugs but since only one cylinder is on the "compression stroke" I assume the other spark is called "wasted?" I have a 1979 Datsun sports car that has a Jetronic fuel injection that seems to do something analogous. It injects a half-charge of fuel on every stroke at every cylinder even though it's a four-stroke. Runs fine, though.

Back to "waste-spark." I've had a problem with several of these systems for years and thus my question. And it's not just me. I was just reading a long similar discussion at an electrical engineering forum and a engineer has the same questions as me.

So, for example - take my 1973 Honda, CL-175 motorcycle. Two cylinder four-stroke-cycle engine, one set of breaker points, and two outputs from the coil to the two spark plugs. When the bike was new it started and ran fine. But once it got around 20 years old, it go so that when first started and cold, it would only run on one cylinder. And it was random. The dead cylinder was not always the same one. So, when first started, all I have to do is pull plug wires, one at a time. If I pull the wire off the cylinder that was firing and pull the plug boot maybe a 1/2" from the plug - a long "lightning bolt" type arc is created and THEN both cylinders fire. It's been this way for years now. Once warm it runs fine and I stick the plug boot back on. I've put in new plugs and a different coil and it made no difference.

Now, to expand. At this electrical engineering forum, one engineer is having the same issue with his two-cylinder car. When it misfires on one cylinder, he says he can totally unhook the other (running cylinder) and then the dead cylinder comes to life. He wants to know how this is possible since . . . he claims one end of the coil secondary has no path to ground. My guess is - that the coil has made a "short" to ground that he's not seeing.

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I saw something similar at Carlisle. They were selling these "Miracle cure" spark increasers for older points style ignitions. It plugged in on top of the distrib and was basically a spark gap that forced the coil to fire at a much higher voltage/energy. I am not sure to what detriment but the car did run much better. Perhaps opening the plug gap would have the same effect? I would agree that some sort of leakage is to blame, but I have no idea how to find it.

Aaron

Fun to have other "sparkies" to chat with on these topics, even if we bore others to tears. As I see it when the coils LV primary collapses (current interrupted when points open) voltage starts to rise across the HV secondary and it only rises high enough to arc jump current across the plug gaps. If the gap is too wide i.e. NO CURRENT PATH (and no leaks or HV breakdown occurs) the voltage will then ramp back down. In that HV double ended secondary coil if EITHER gap was too wide OR LIKEWISE IF THERE WAS NO TO GROUND PATH (on either end) I dont see any plug firings and that agrees with your conclusion THERE HAS TO BE A TO GROUND PATH SOMEWHERE which may consist of a HV insulation breakdown somewhere in the loop. If such continues to happen furthere insulation damage will take place and carbon tracking and eventually trash the coil completely.

I dont see how in theory this is any different then when theres a regualar coil but theres no plug wire attached nor anyplace current can arc, the plug simply fails to fire well DUHHHHHHHH. If alls well if you remove one plug wire in the loss spark system I dont see how the remaining plug can fire UNLESS THERES AN ARC PATH SOMEWHERE !!!!!!!!!!

NOTE 1 the coil is capable of achieveing far higher voltage then that normally required to fire the plug, say 10,000 or so volts, depending on plug gap and compression etc HOWEVER if theres an open like one plug is removed etc THE VOLTAGE WILL RISE MUCHHHHHHHHHHH HIGHER THEN NORMAL and when that happens unintentional arcing and HV insulation breakdown can occur that would NOT otherwise with both plugs installed, and if left unchecked the coil (it HV withstand ability) eventually fails.

NOTE 2 This reminds me of the age old farmers trick that when a plug is misfiring he pulls the plug wire off but with maybe a 1/4 inch gap left between the wire end and the plug and it starts firing but thats another story.....

What say you???
What do the "experts" on the other board think

I been retired as an EE since 91 so rusty as an old nail on all this but this is my story n Ima stickin to it

PS If you remember the RV battery discussion, Im leaving my three 12 volt identical 125 AH units all connected in paralell for now (375 AH) its working great, but in the future when they eventually fail Im going back to two L 16 (290 AH) true deep cycle 6 volt batteries in series
and use of a 3 stage "smart" charged designed for deep cycle battery charging and maintenance and oughta get 10 yrs out of that I figure. The thing is now (unless I change over) Im having to use the cheap run of the mill (NOT smart or 3 stage) RV Converter/Charger which charges the house batteries when Im plugged in. Just last week, however, I added an On/Off switch so when Im plugged in for weeks at a time the Converter/Charger can be disconnected from the house batteries (as needed, monitoring voltage) to avoid any overcharging or boiling over those expensive batteries. When plugged in my 12 volt loads are Converter powered so they all still work even if I disconenct the house batteries. Last week my RV was under roof but the roof solar panel was still producing slightly (maybe 1 to 2 amps) and the house batteries were stabilized at 13.22, then when I plugged in they rose to 13.68 but later settled at 13.45 SO I THINK IM OKAY FOR NOW, it may not even be necessary to disconenct the charger (they never lost electrolyte last year wehn plugged in constantly) but I like my added switch just in case.

Ol John T and all, BSEE, JD retired

Thats the same as the old farmers trick (when plugs are fouling) of pulling the plug wire off but leaving it maybe 1/4 away from the plug end. When the coil stores energy its X joules finite amount which gets expended in the form of Volts x Amps x Time when the plug fires. THEREFORE if the voltage is increased (wider gap) the current or arc duration is less, thats why the spark will change from a thick blue to a faint thin wimpy yellow. The wider gap causes the coil voltage to have to rise higher perhaps causing it to run tad hotter, work harder, and maybe at less efficieny overall but it can cause a fouling plug to start firing again. Looks to me like its a choice between changing plugs or curing the fouling (rings, valve guides etc) or running a wider gap (may or may not reduce coil life) ???

John T

Honda MC systems are based on the open system as shown in your diagram. As John T points out, the onlyt ground path is the electrode in one plug, through the head aluminum, to the other plugs ground electrode then center electrode, then back to the coil other winding. In fact there is only one winding in the Honda coil with plug wires attached at each end of that winding, whereas your diagram has a connection between two windings (same reality).
There is no reason I can think of that would preclude the use of two coils on one set of points in a conventional setup, that is with the center connection in your diagram connected to the points as the primary is connected to the secondary in a "normal" ignition coil. This would allow the ground circuit to be established with one wire off the plug and not grounded.
This might also explain why the removal of the non operating (fowled) plugs wire might allow the other to operate due to opening a shorted secondary. Just thinking. Jim
honda

Glad, as always, to hear your "professors" thoughts on these sparky topics. Some guys jury rig double coils like you mentioend to a single set of points, of course that works, I only warn them if the points have to now switch a lot more current then the typical 4 maps max, they will burn up much faster.

Gotta run headed to the Legion Hall

John T

think of it as a water spigot with a divider and two hoses. as long as every thing is equal both hose have equal flow . but if you squeeze one with your hand the other hose pressure increases. i suspect your motorcycle for some reason has a higher resistance to fire the one cylinder, may be compression or fuel air mixture. for some reason that cylinder is needing more amperage to ignite. when you un plug the good cylinder all the amps go to the bad one and then it starts hitting.

In my Honda tech manual for my 1973 CL-175, it does show a mid-year change. The early bike (like mine) has one set of points and one coil with dual secondary outputs. The late-year Honda changed over to dual points and dual coils. I.e. one set of points and one coil for each cylinder. I'm wondering why they did this? Cost or better performance?

Whatever, this problem has me somewhat stumped. I'd suspected that maybe a coil can develop an internal path from the secondary to ground and thus cause this problem. I DID try another used coil but can't say I know for sure it does not have the same problem.

Also as another poster mentioned, I've wondered about unequal fuel-air ratios between one cylinder to the other. But the problem is not dedicated to any one cylinder. It is random. I've never spent any money to try to fix this bike since once warm, it runs fine and will do so all day long with issues.

Read down for the "car model" stuff.

The concept of "potential" voltage versus "actual" voltage to fire a spark plug is not foreign to me. A clean plug gapped at .025" in a combustion chamber with correct air-fuel ratio might only need around 8000 volts to fire. Add another 2000 volts if there is a distributor-rotor to arc across. Add some high-resistance wires and/or plugs and the need goes up.

But - I still can't figure . . . if the spark path is basically in series with two spark plugs - how can one can fire and one fail to fire. I'm having trouble wrapping my brain around it. If one does NOT fire, there is no known path to ground, correct? Maybe they both DO fire, but one is so weak that cylinder will not perform? I'd buy that if just one cylinder had this problem, but that is not the case.

Electricity probably flows in one direction, yet it has never really been proven. Thus the "Hole Theory" and the "Electron Theory." We figure it's moving and we put labels and tell stories about it. Modern circuits and solid-state components are built on "predicted" behavior of those mysterious electrons. And gravity pulls on us with "gravitons". . . another unproven mystery. And as we now, not all matter suffers from good-old Newtonian gravity.

I still remain a bit stumped.

In regard to the electrical engineering forum, many are citing long forumlas based on theory but in essence - nobody has come up with anything that hasn't been posited here. The guy on that forum has the same problem as me, but his is with a 2CV Citroen car (the longest lived car model in the world last I checked). But "long lived" is defined in different ways. Citroen 2CV was made for 42 years without huge changes. But, some argue that Chevrolet has made the Corvette for 58 years. I DO recall that GM ended it's production a few years back -but then quickly reversed that decision. Either way, today's Corvette isn't much like the 6 cylinder version of 1953. Then the Volks Beetle? Volkswagen brags about 71 years - but that seems "iffy" to me. Certainly isn't air-cooled anymore. Some claim that the Morgan 4/4 breaks all records. 75 years and still being made with one short break during one or two years. Oh well, seems I've gone off the topic.

In regard to charging your deep-cycle batteries with a standard charger with slightly less voltage? I know many people who have done it for years with no ill-effects. Just means your RV batteries never reach their absolute maximum charge. Maybe 98 % instead of 100 %.

"Equalization" seems to be the most important battery maintenance issue -going by what battery makers claim. It means little if all you have is a few batteries. But, if you have a large bank with 6,8, 10 batteries or more - it takes a huge charger to put out the amps to "equalize" or "over-volt" those batteries. My Trace charger that's built into my 2000 watt inverter has a 120 amp at 15 volt charge capacity. That's pretty big.

My vote is on "arcing over somewhere (maybe insulation breakdown in the disconnected wire to metal structure) maybe inside the coil itself. On the bench, when a coil is driven by quiet solid state switching components &amp; I have no connection to the HV output, there is still an audible noise coming from the coil at lower voltages. Once input voltage is high enough, it arcs over the tower. Now, at those lower input voltages, is it internally arcing, or am I hearing lamination rattle, or what? Another bench observation: I have discharged a large capacitor through a SCR and associated connecting wire and even though there is no moving contacts &amp; such, there is stoll an audible noise......what is that? Guess something somewhere is moving to make that noise.

Wouldn"t it be just opposite? 2 coils = more resistance & less current through the points.

Just to add a little here, I see no one has brought up the aux gapped spark plug. It had a gap built in the center electrode before it reached the tip of the plug. Champion was pushing those real hard for a while and were putting them in some new engines. First time I ever saw them was when servicing a new IH pickup and I could hear this spark snapping. Finally determined it was from that aux gap and in the dark you could see it as the plugs did not have a complete insulator cover over them. They dropped out of favor very shortly as that gap would grow too wide and cause engine missfires. I used to break them apart just to take a look at how much they had burned away.

But the 2 coils (when they jury rig 2 regular coils to replace the system above) are in paralell with a common voltage on their inputs yet BOTH outputs switched via a single set of common points. Typically each coil draws 4 amps so the 2 will draw 8 amps causing the points to burn up fairly quick..

John T

Your question:

"But - I still can't figure . . . if the spark path is basically in series with two spark plugs - how can one can fire and one fail to fire"

My response:

If theres an arcing path on the bad side of the coil (i.e. the side where the plug is that doesnt fire) the other (good side) can still fire its plug since on the side with the short (HV breakdown fault) the short provides the path instead of current arcing across the plugs gap. If you short out one plug wire the other still fires, and the same thing can happen if on one side of the coil a breakdown is allowing arcing current to flow at a place OTEHR THEN the plug.

John T

i think the higher the compresion ratio the greater spark must be

Its my similar contention that if compression rises, it takes a higher voltage to arc jump current across the gap. Extreme high compression racing engines use HV coils that have the capacity to rise to higher firing voltages as necessary to fire the plugs.

John T

Yes and no. If the two primaries were in series, yes (very possible) if they were parallel it would double. The functional truth is that the engineers would make sure that the point current load was modestly within the capacity for switching by putting the correct resistance in the primary coils either way. There could also be just one primary and two secondary windings! Jim

Another answer in addition to johns is that 90 % of plugs that fail fail with a short. The voltage travels either through a whisker of conductive trash between the electrodes, or down the side of the center electrode through condictive deposits to the shell. Not firing does not mean not getting voltage, nor does it mean that the plug is "open". Modern Fuel is so much cleaner than leaded garbage we tollerated for 3/4 century that plugsnow last 100,000 miles instead of 7500. They still foul in an oil burning tractor, but even then less than before. Jim

HEYYYYYYYYYYYY Professor, I think I like that answer better then mine. A plug effectiverly shorted by conductive fouling material (say oil or carbon) doesnt produce any external hot current arc to ignite the fuel air mixture BUTTTTTTTT the short still provides a current path thereby allowing the other good plug (or good conditions) to still fire........

Go to the head of the class

John T

HEYYYYYYYYYYYY Professor, I think I like that answer better then mine. A plug effectiverly shorted by conductive fouling material (say oil or carbon) doesnt produce any external hot current arc to ignite the fuel air mixture BUTTTTTTTT the short still provides a current path thereby allowing the other good plug (or good conditions) to still fire........

Go to the head of the class

John T

I've seen it happen many times, especially in plugs that were too hot. The insulators became conductors.

None of this applies to my problem. I've swapped plugs many times and also the coil.

Your shorting/arcing/conducting path must be elsewhere then (no plug firing otherwise) but where???????? Coil?? Wires?? Plugs??

Good luck finding it, let us know what you find

John T

Quote [Its my similar contention that if compression rises, it takes a higher voltage to arc jump current across the gap. Extreme high compression racing engines use HV coils that have the capacity to rise to higher firing voltages as necessary to fire the plugs.
John T ]

John T ,I liked to do that "quenching" of the spark,on a multitude of spark plugs, both aero and auto, using the Champion Spark Plug tester and a large compressor.

Some plugs would quench at a relatively low pressure whilst others would still be sparking with the pressure way up.


Alont

Yep it would be good to see some good accurate data and experiments with charts to show actual firing voltage as a function of rising (above atmosphere) compression given all other (fuel mixture, RPM, etc) factors remaining the exact same. I've read on the topic long ago and at the risk of big time OVERSIMPLIFYING seems like it had to do with at higher compression (i.e. increased density) theres more molecules n "stuff" in the way between the electrodes and it was harder to get current to arc jump thru all the "crap" lol hows that for a technical explanation??

Fun chat maybe we can all learn something..

An ever still curious, Ol John T

John T
I used to havea SL-175 that had that system and I found that with a week or low Battery it would fire on one cyl. I just replaced battery with a new one charged to full cap and the problem would go away.

I had a problem with hard starting and one cylinder misfiring under heavy load on a B&S 17 hp boxer engine.

The thing was miserable cold starting, I had to keep the throttle closed to keep the cylinder pressure low and choke until it would idle off.
Once running, it would miss on one cylinder under a heavy load.
I changed plugs several times, (tried different brands and heat ranges) with no fix for the problem.
I thought it had to be a weak mag coil, so I replaced that, but gained nothing.
I suspect now that the flywheel magnets are weak, leading to the weak spark.(coil gap is correct)

I had plug fouling problems with a couple little 2 cycle engines, that were fixed by installing E3 brand lawn and garden plugs. I only tried them because of their guarntee that they would not foul, suspecting that they were just another non working gadget. I was wrong (happily they cured the 2 cycle starting and fouling problems.
I thought, they worked so well in the little 2 cycle motors, why not try them in that cranky B&S four cycle.
I installed E3 plugs in it and immediatly saw a dramatic difference, I could now cold start it with the throttle open, allowing full cylinder pressure, and it started in the first few turns of the engine. The heavy load misfire on one cylinder is also gone. That set of plugs is in there for 5 seasons of mowing the lawn, still starts and pulls great.

In the case of the E3 plugs, their really are magic sparkplugs, that will in part compensate for a weak ignition system or some engine wear caused fouling.
They might be worth a try, they work for me.

Electricity takes all paths available to it in inverse proportion to the impedance of the paths. This strikes down the old theory: "electricity takes the path of least resistance". You may have many, many paths, or just a few, or, unlikely (especially in an old tractor), only one. This may explain your problem. A problem which can be best evaluated in total darkness with the engine running. It used to be commonly called: "The firefly check". (;>))

John T and Janicholson have it right. The misfiring plug is fouled so it's short-circuiting the spark for that plug but allowing a ground path for the good plug.

The question remains "why does pulling the good plug make the bad one fire?". I suspect you'll get the same results if you pull either plug; this is a phenomena you'll see with fouled plugs on more conventional distributor systems: pulling the wire off a bad plug can make it fire. What is happening is that the voltage must rise significantly to jump the gap between plug wire and plug. The voltage produced by an ignition coil is limited only by the spark gap; the wider the spark gap the greater the voltage. The higher voltage will arc across the fouled plug rather than discharging through the short.

The description in the service manual for Saturn cars says that if the circuit for one plug becomes open the other is grounded through the ignition module. That leads me to believe that there is a circuit in there that has a higher resistance than is normally encountered in the secondary ignition circuit so it only becomes a factor if the resistance for one of the plugs goes out of its normal range.

JC Whitney used to sell these little caps to put on your spark plugs which claimed to solve misfiring due to oil fouling etc. Later on there was a larger device which plugged into the center post of the distributor. I remember breaking these apart and they were nothing more than a gap the spark had to jump. In a similar vein there were "Booster Gap" plugs from the major spark plug makers which had the gap built into the plug.

Reference, Dykes Automotive... Encyclopedia, Thirteenth Edition, 1923; Page 237.

Spark Intensifier: "The purpose is to provide a gap in series with the high-tension circuit for the spark to jump before it reaches the plug. It is claimed that this will intensify or raise the voltage of the high-tension circuit to such an extent that it will jump across a carbonized plug in spite of its fouled conditon".

It goes on to discuss various spark plug problems (carbon leak paths) and how they could result in mis-fire. The action of the intensifier gap is explained as follows.

The Action: ...."If the intensifier gap is provided, this temprorarily acts as a dam to the flow of current, and, like flowing water, it will pile up against the dam and thus establish a greater force when released. After the breakdown of the dam, the current comes with such a rush that it connot all pass through the carbon path, and as its voltage is now sufficient, it will also jump the spark-plug gap".

Rather than the dam analogy, I have also seen it explained it in terms of ignition rise time. As the magnetic field in the coil primary collapses the high voltage induced in the secondary coil winding does not occur instantaneously but rather increases over time. Conductive deposits on the spark plug can bleed this voltage off before it can increase to a level sufficient to jump the plug gap. The spark gap reduces the rise time since the voltage (across the gap) must increase to high level to ionize the large gap. Once ionization occurs the air in the spark gap becomes conductive and current flow is immediate - thereby jumping the spark gap and the plug gap.

In conclusion, pulling the spark wire away from the spark plug is simply acting as a spark intensifier. The effect is the same regardless if the plug wire is removed from the firing cylinder or the mis-firing cylinder as long as the spark is allowed to jump to the plug.

As to the question of how one can remove the wire from the firing cylinder and not allow a spark to jump to the plug I could only speculate. Perhaps the coil secondary is center tapped and grounded or otherwise finds a ground as other posters have suggested. However, it is not stated what is done with the wire after it is removed from the firing cylinder. If it is left to lay against the engine a spark may be jumping across the rubber terminal boot to ground - acting as a spark gap.

I am not an electrical weenie however, this is how it fits into my head.