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Originally posted by TourDeForce:
If the plug wire or coil is going bad, it causes a mis-fire. The ECU then kicks up the voltage to the suspect cylinder to try & force spark through the plug & avoid damage to the engine. As the voltage spikes, this raises heat within the plug causing the core to expand & burst the insulator.
So, you can have good plugs in the engine, but if the wires or coil create too much resistance, the ECU still must raise the voltage to get adequate spark to that plug and poof, the plugs burst from the excess heat that is generated from an over-voltage condition.
JimR
Let me try to clear this up. The ignition coil is designed to have a specific maximum voltage. As ignition systems have improved over the years this maximum voltage has increased from 25,000 volts to something in the neighborhood of 60,000 volts. This maximum voltage is referred to as the AVAILABLE voltage.
The ignition system usually doesn't operate at AVAILABLE voltage. It operates at the REQUIRED voltage. The REQUIRED voltage is what is required to get the spark to jump across the gap. There are several things that will alter REQUIRED voltage, but chief among them is cylinder pressure. Some others are fuel mixture and spark plug condition. As the cylinder pressure rises creating more horsepower, the voltage required to fire the plug rises.
The difference between the AVAILABLE voltage and REQUIRED voltage is the RESERVE voltage.
When the REQUIRED voltage rises above the AVAILABLE voltage, or when there is no more RESERVE voltage, there will be a misfire.
One of the main reasons that spark plugs last as long as they do today is because the AVAILABLE voltage is so high that it will fire a plug that is worn so bad that it would have created a miss in engines of just a few years ago. Platinum tips also help in that they do not wear as fast.
So the idea that a processor of some sort increases the voltage to the plugs is hog wash.
Jim Johnson
98 SVT
03 Escape Limited
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Just to add to Big Jim's response, the voltage required to jump the gap is not calculated, it is the actual point when the voltage jumps "on its own". Once the spark starts, the voltage cannot rise any further as the spark is "shorting" the voltage. As compression values rise (throttle increase, load increase) the voltage level needed to cross the gap rises. The gap acts as a resistor in the circuit. Resistor wires and resistor plugs actually cause a minimum voltage that will be available to the plugs. The old point sytems actually had the same response, but coils then had less available voltage.
Bigger gaps cause hotter, bigger sparks, AS LONG AS THE COIL CAN DELIVER THEM. If the necessary voltage cannot be delivered, a misfire occurs. So too little a gap requires less voltage-gives a smaller less powerful spark (and a possible misfire). Too large a gap exceeds the capacity of the coil and causes a misfire.
On a further note, sparks always jump easiest from sharp edges. When the electrodes are worn down into a rounded shape, the required voltage increases. Thin wire platinum plugs maintain their edges longer both from the hardness of the platinum and the thin form factor. That's why the dual plat's work best in our engines.
My name is Richard. I was a Contouraholic.
NOW: '02 Mazda B3000 Dual Sport, Black
BEFORE: '99 Contour SE Sport
Duratec ATX Spruce Green
PIAA 510's, Foglight MOD, K&N Drop-in
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Originally posted by Rogerm60:
"or leakage which drains energy causing a spark somewhere besides the plug's tip. As most books will tell you, shattered plug insulators are usually caused by detonation. Crossfire between leaky plug wires can cause occasional detonation. Detonation causes drastically increased pressures within the cylinder and can damage plug tips and ceramic insulators.
OK, so my question is, how DOES detonation break an insulator ? The insulator is not inside the combustion chamber. Can detonation be forceful enough to travel way up inside the plug and crack the ceramic from the inside ? Is the ceramic that insulates the tip part of the exterior ceramic ? It would seem to me that if there was sufficient catastrophe to the plug tip inside the combustion chamber that the force would destroy the tip long before it could crack the insulator outside. It seems as if the tip looked untouched that it would be extremely unlikely that the ceramic could be broken on the outside. Please esplain yourself Lucy, and thanks for all the input so far, it has been very interesting and informative.
Ken, 99 Silver Frost SE Zetec Atx, polished alloys, Kumho's, Pioneer hi power CD/AM/FM. Factory spoiler (added) Audi side lites, Borla stainless steel muff. Stolen, recovered in pieces. Looking for another Tour, preferably V6, 5 speed.
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Originally posted by Kennard:
Originally posted by Rogerm60:
"or leakage which drains energy causing a spark somewhere besides the plug's tip. As most books will tell you, shattered plug insulators are usually caused by detonation. Crossfire between leaky plug wires can cause occasional detonation. Detonation causes drastically increased pressures within the cylinder and can damage plug tips and ceramic insulators.
OK, so my question is, how DOES detonation break an insulator ? The insulator is not inside the combustion chamber. Can detonation be forceful enough to travel way up inside the plug and crack the ceramic from the inside ? Is the ceramic that insulates the tip part of the exterior ceramic ? It would seem to me that if there was sufficient catastrophe to the plug tip inside the combustion chamber that the force would destroy the tip long before it could crack the insulator outside. It seems as if the tip looked untouched that it would be extremely unlikely that the ceramic could be broken on the outside. Please esplain yourself Lucy, and thanks for all the input so far, it has been very interesting and informative.
Detonation does not break the external portion of the insulator.
Detonation can break the inner portion of the insulator, the cone, that is exposed to the combustion chamber.
The external part of the insulator is broken by mechanical damage, usually during installation.
Sometimes (but very rare) a poorly made spark plug may blow apart so that the ceramic portion slips out of the matal shell. In my experience, this was more common with Champion plugs, but I have seen it on others. Although extreme cylinder pressure (including spikes in pressure from detonation) can contribute to this, it is mostly a problem with building the plug.
Jim Johnson
98 SVT
03 Escape Limited
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Originally posted by Big Jim:
Detonation does not break the external portion of the insulator.
Detonation can break the inner portion of the insulator, the cone, that is exposed to the combustion chamber.
The external part of the insulator is broken by mechanical damage, usually during installation.
Sometimes (but very rare) a poorly made spark plug may blow apart so that the ceramic portion slips out of the matal shell. In my experience, this was more common with Champion plugs, but I have seen it on others. Although extreme cylinder pressure (including spikes in pressure from detonation) can contribute to this, it is mostly a problem with building the plug.
I was told this also, and it makes sense, but, I've had 6 plugs, 2 Autolites and 4 Motorcrafts with broken insulators. Always in the same place, on the top part of the ceramic insulator, above the built in hex nut used for installation. I was accused of breaking the plugs by the dealer, so I had the dealer install them, a week later I had 2 broken plugs. So I know it wasn't me, and it wasn't defective plugs. So something else is breaking them, but what ? How can a bad plug wire break the insulator ? Since I replaced my plug wires I have had no plugs go bad. Before I pulled the plug wires off to R&R my original plugs I never had a plug go bad. So I am just trying to envision how the insulators break, and I just can't. I'm hoping someone here who is smarter than I (that won't take much) can explain to me how it is that this happens, thank you.
Ken, 99 Silver Frost SE Zetec Atx, polished alloys, Kumho's, Pioneer hi power CD/AM/FM. Factory spoiler (added) Audi side lites, Borla stainless steel muff. Stolen, recovered in pieces. Looking for another Tour, preferably V6, 5 speed.
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Originally posted by Kennard:
Everyone I talked to had never heard of this problem, with the exception of a few of you here. This problem is somehow related to the plug wires. I think it's the boots that went bad from me pulling them out to R&R the plugs the first time. I think I cracked them when I pulled them off the plugs, and somehow the spark is shorting out to the head through the middle of the plug instead of arcing across the gap. Therefore the broken insulators. But it's that part of it that I don't understand, it seems like there would be alot more resistance to go through the insulator and out to the head than to just continue on to the tip and across the gap. But I got the same questions from almost everyone, "are you sure you didn't break them yourself" ? "Did you drop them ? Did you overtighten them ? Did the plugs flop around inside the plug wrench" ?
Kennard,
You haven't spoken to any Technicians at your local FORD Dealers.
When my car was NEW, I had gotten a CEL twice.
The first time they dismissed it, and the second time I had TWO PLUGS and TWO WIRES
replaced because of misfires caused by broken plug insulators.
I asked how they could break, and I was told that sometimes the ceramic material
could have a hairline crack in it when the plug is assembled.
The crack is not enough for the plug to fail inspection or a quality test,
but when the spark plug is put into use and it heats and cools over a period of time,
the crack will grow and cause the plug to fail.
Detonation will accelerate this process.
Pete...
2004 Mercury Marauder 300A
Black Clearcoat/Dark Charcoal LEATHER
DOB 10/31/2003
DOP 1/2/2004
www.mercurymarauder.net
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Originally posted by RoadRunner:
Kennard,
You haven't spoken to any Technicians at your local FORD Dealers.
When my car was NEW, I had gotten a CEL twice.
The first time they dismissed it, and the second time I had TWO PLUGS and TWO WIRES
replaced because of misfires caused by broken plug insulators.
I asked how they could break, and I was told that sometimes the ceramic material
could have a hairline crack in it when the plug is assembled.
The crack is not enough for the plug to fail inspection or a quality test,
but when the spark plug is put into use and it heats and cools over a period of time,
the crack will grow and cause the plug to fail.
Detonation will accelerate this process.
Actually I have spoken to many Ford dealers, and it was the last Ford dealer who sort of got me on the right track with the Motorcraft plugs. But that guy said an engine couldn't break the insulator of a plug. He (the parts mgr) told me to go see the service mgr, who was a 'tune-up expert', THAT guy told me that it was either me dropping them or breaking them upon installation, or there was a problem in production. So I had the dealer install a set, they still broke. Just like the previous 2 sets, so yes, I have seen Ford dealers, lots of them. And for the record, I never did get a CEL. I was told the same thing about the plugs, that there could be a hairline crack, invisible to the naked eye. Which honestly, was a crock, the dealership was trying to cover up the fact that they had no idea.
Ken, 99 Silver Frost SE Zetec Atx, polished alloys, Kumho's, Pioneer hi power CD/AM/FM. Factory spoiler (added) Audi side lites, Borla stainless steel muff. Stolen, recovered in pieces. Looking for another Tour, preferably V6, 5 speed.
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