Burned Coils
06-25-2004, 02:44 PM
#1
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Burned Coils
No i haven't burnt mine. But with the amount of burned coils we are seeing recently i thought perhaps we could have one thread to discuss. When I first started reading the reports it seemed as if it was related to the CZ unit because it was only Stage 1 folks who were reporting it.(Except maybe MazdaManiac-but still a modded car)
Now I am seeing more posts from owners of completly stock 8's. Some seem to be on newer flashes but at least one i read was on a previous flash when the coils went and were given M during the diagnosis/repair phase.
So since i am am not an Ignition Guru perhaps we can get some posts in here from some who know more and maybe educate us and perhaps find a reason for the burned coils.
Now I am seeing more posts from owners of completly stock 8's. Some seem to be on newer flashes but at least one i read was on a previous flash when the coils went and were given M during the diagnosis/repair phase.
So since i am am not an Ignition Guru perhaps we can get some posts in here from some who know more and maybe educate us and perhaps find a reason for the burned coils.
06-25-2004, 03:02 PM
#2
Recovered Modaholic
A factory engineer told me a likely cause for burnt coils is the motor running lean. I've read threads discussing the CZ leaning out the AFR so it makes sense.
06-25-2004, 10:40 PM
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The ignition coils are composed of a transformer (the coil) and a power transistor that grounds the primary. The other side of the primary is connected to +12V and there is a capacitor to ground from that power source (used by all four coils). It's on the top of the engine under the intake manifold.
The PCM sends out a 5 mS 5V pulse to fire a coil. First the coil "charges up" (inductively - a magnetic field builds), then when the 5 mS pulse ends the transistor opens and the coil discharges - sending a spark out the secondary. BTW, the coil has an inductance of 1.8 mH - so you can compare it to aftermarket ones. Just remember, you can't replace it with just a coil, it has to be a coil with an internal grounding power transistor.
Good things about this system:
It keeps the PCM cooler as it doesn't have to deal with high currents through coils.
It allows the manufacturer to select coil suppliers as it's kind of a "standard layout".
It is inexpensive and simple. The coils retail for around $60 US each. Cheap for automotive electronic coils.
Bad things about this system:
You are stuck with stock coil energy as the 5 mS charge time limits how much you can store in the coil. If you could change that time you could put in a larger coil and charge it for say, 7 mS.
The transistor is the weak part as it will see around 400 V when the coil discharges, and has to not conduct that or be damaged by it. When you heat up a transistor it becomes less tolerant of that 400 V pulse. Also, the transistor is used as a switch - that is it should have minimal voltage drop across it when turned "on" by the PCM. If the transistor looses enough gain it will not saturate (turn on all the way), and there will be higher voltage drop across it. The power that the transistor has to dissipate is the voltage across it times the coil current (when it is charging the coil).
Transistors loose gain when heated. -IF- the coil (with the transistor embedded in it) gets hot enough to drop the gain of the transistor enough to come out of saturation, it will get hotter still, which will take it further out of saturation, etc. It's called thermal runaway.
If you notice your car suddenly idling very rough, or suddenly performing very poorly, pull over and stop, shut off the engine and pop the hood to let it cool off. You may save your coils from thermal runaway.
Notice how the coils are in the radiator air output stream? You can see the row of the four coils under the intake rubber tube. Do you think this air stream -may- heat the coils?
As for the CZ impacting coil life, remember, those with the CZ will be more likely to be running the car hotter (autocross' etc), so will be more at risk of damaging the coils by overheating. It also took us a little time to understand the interaction of the box with the stock system parts, and adapt to it. We believe our box now will tolerate weak coils better than the stock system, and may even protect the coils more as it drives the transistor a little harder into saturation.
The PCM sends out a 5 mS 5V pulse to fire a coil. First the coil "charges up" (inductively - a magnetic field builds), then when the 5 mS pulse ends the transistor opens and the coil discharges - sending a spark out the secondary. BTW, the coil has an inductance of 1.8 mH - so you can compare it to aftermarket ones. Just remember, you can't replace it with just a coil, it has to be a coil with an internal grounding power transistor.
Good things about this system:
It keeps the PCM cooler as it doesn't have to deal with high currents through coils.
It allows the manufacturer to select coil suppliers as it's kind of a "standard layout".
It is inexpensive and simple. The coils retail for around $60 US each. Cheap for automotive electronic coils.
Bad things about this system:
You are stuck with stock coil energy as the 5 mS charge time limits how much you can store in the coil. If you could change that time you could put in a larger coil and charge it for say, 7 mS.
The transistor is the weak part as it will see around 400 V when the coil discharges, and has to not conduct that or be damaged by it. When you heat up a transistor it becomes less tolerant of that 400 V pulse. Also, the transistor is used as a switch - that is it should have minimal voltage drop across it when turned "on" by the PCM. If the transistor looses enough gain it will not saturate (turn on all the way), and there will be higher voltage drop across it. The power that the transistor has to dissipate is the voltage across it times the coil current (when it is charging the coil).
Transistors loose gain when heated. -IF- the coil (with the transistor embedded in it) gets hot enough to drop the gain of the transistor enough to come out of saturation, it will get hotter still, which will take it further out of saturation, etc. It's called thermal runaway.
If you notice your car suddenly idling very rough, or suddenly performing very poorly, pull over and stop, shut off the engine and pop the hood to let it cool off. You may save your coils from thermal runaway.
Notice how the coils are in the radiator air output stream? You can see the row of the four coils under the intake rubber tube. Do you think this air stream -may- heat the coils?
As for the CZ impacting coil life, remember, those with the CZ will be more likely to be running the car hotter (autocross' etc), so will be more at risk of damaging the coils by overheating. It also took us a little time to understand the interaction of the box with the stock system parts, and adapt to it. We believe our box now will tolerate weak coils better than the stock system, and may even protect the coils more as it drives the transistor a little harder into saturation.
06-25-2004, 10:49 PM
#6
Recovered Modaholic
My 8 is stock (no CZ) and I burned the primary coils when the fuel filter got saturated and blocked. The fuel restriction caused a lean misfire (CEL) at high revs and the coils overheated.
06-25-2004, 10:59 PM
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That is possible, as the lean condition could cause the sparkplugs to heat up and conduct and act as a short, and that would put extra energy back into the coil - it would in effect reflect back from the plugs as they would no longer be "impedance matched".
06-25-2004, 11:12 PM
#8
Recovered Modaholic
It was a dark time for me. It took almost 2 months to get it figured out. The car ran fine up to about 6k then it went flat. Driving an 8 without going over 6k is torturous 
06-27-2004, 03:19 PM
#9
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I thought maurice said it was a 3.3v 4ms duration? or was that something different?
Not that it makes any diff to me, just making sure I understand.
Not that it makes any diff to me, just making sure I understand.
Originally posted by RX-8 friend
The ignition coils are composed of a transformer (the coil) and a power transistor that grounds the primary. The other side of the primary is connected to +12V and there is a capacitor to ground from that power source (used by all four coils). It's on the top of the engine under the intake manifold.
The PCM sends out a 5 mS 5V pulse to fire a coil. First the coil "charges up" (inductively - a magnetic field builds), then when the 5 mS pulse ends the transistor opens and the coil discharges - sending a spark out the secondary. BTW, the coil has an inductance of 1.8 mH - so you can compare it to aftermarket ones. Just remember, you can't replace it with just a coil, it has to be a coil with an internal grounding power transistor.
Good things about this system:
It keeps the PCM cooler as it doesn't have to deal with high currents through coils.
It allows the manufacturer to select coil suppliers as it's kind of a "standard layout".
It is inexpensive and simple. The coils retail for around $60 US each. Cheap for automotive electronic coils.
Bad things about this system:
You are stuck with stock coil energy as the 5 mS charge time limits how much you can store in the coil. If you could change that time you could put in a larger coil and charge it for say, 7 mS.
The transistor is the weak part as it will see around 400 V when the coil discharges, and has to not conduct that or be damaged by it. When you heat up a transistor it becomes less tolerant of that 400 V pulse. Also, the transistor is used as a switch - that is it should have minimal voltage drop across it when turned "on" by the PCM. If the transistor looses enough gain it will not saturate (turn on all the way), and there will be higher voltage drop across it. The power that the transistor has to dissipate is the voltage across it times the coil current (when it is charging the coil).
Transistors loose gain when heated. -IF- the coil (with the transistor embedded in it) gets hot enough to drop the gain of the transistor enough to come out of saturation, it will get hotter still, which will take it further out of saturation, etc. It's called thermal runaway.
If you notice your car suddenly idling very rough, or suddenly performing very poorly, pull over and stop, shut off the engine and pop the hood to let it cool off. You may save your coils from thermal runaway.
Notice how the coils are in the radiator air output stream? You can see the row of the four coils under the intake rubber tube. Do you think this air stream -may- heat the coils?
As for the CZ impacting coil life, remember, those with the CZ will be more likely to be running the car hotter (autocross' etc), so will be more at risk of damaging the coils by overheating. It also took us a little time to understand the interaction of the box with the stock system parts, and adapt to it. We believe our box now will tolerate weak coils better than the stock system, and may even protect the coils more as it drives the transistor a little harder into saturation.
The ignition coils are composed of a transformer (the coil) and a power transistor that grounds the primary. The other side of the primary is connected to +12V and there is a capacitor to ground from that power source (used by all four coils). It's on the top of the engine under the intake manifold.
The PCM sends out a 5 mS 5V pulse to fire a coil. First the coil "charges up" (inductively - a magnetic field builds), then when the 5 mS pulse ends the transistor opens and the coil discharges - sending a spark out the secondary. BTW, the coil has an inductance of 1.8 mH - so you can compare it to aftermarket ones. Just remember, you can't replace it with just a coil, it has to be a coil with an internal grounding power transistor.
Good things about this system:
It keeps the PCM cooler as it doesn't have to deal with high currents through coils.
It allows the manufacturer to select coil suppliers as it's kind of a "standard layout".
It is inexpensive and simple. The coils retail for around $60 US each. Cheap for automotive electronic coils.
Bad things about this system:
You are stuck with stock coil energy as the 5 mS charge time limits how much you can store in the coil. If you could change that time you could put in a larger coil and charge it for say, 7 mS.
The transistor is the weak part as it will see around 400 V when the coil discharges, and has to not conduct that or be damaged by it. When you heat up a transistor it becomes less tolerant of that 400 V pulse. Also, the transistor is used as a switch - that is it should have minimal voltage drop across it when turned "on" by the PCM. If the transistor looses enough gain it will not saturate (turn on all the way), and there will be higher voltage drop across it. The power that the transistor has to dissipate is the voltage across it times the coil current (when it is charging the coil).
Transistors loose gain when heated. -IF- the coil (with the transistor embedded in it) gets hot enough to drop the gain of the transistor enough to come out of saturation, it will get hotter still, which will take it further out of saturation, etc. It's called thermal runaway.
If you notice your car suddenly idling very rough, or suddenly performing very poorly, pull over and stop, shut off the engine and pop the hood to let it cool off. You may save your coils from thermal runaway.
Notice how the coils are in the radiator air output stream? You can see the row of the four coils under the intake rubber tube. Do you think this air stream -may- heat the coils?
As for the CZ impacting coil life, remember, those with the CZ will be more likely to be running the car hotter (autocross' etc), so will be more at risk of damaging the coils by overheating. It also took us a little time to understand the interaction of the box with the stock system parts, and adapt to it. We believe our box now will tolerate weak coils better than the stock system, and may even protect the coils more as it drives the transistor a little harder into saturation.
06-27-2004, 08:38 PM
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The PCM puts out a 5 volt 5 mS pulse. The coils load it down to about 3 V. With our box installed, you see the 5 V there because we don't load down the PCM output. Our box also supplies more output (lower impedance output, not higher voltage) to the coils - hence the reason I think they will be more resistant to thermal runaway.
06-28-2004, 10:06 AM
#11
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Ok I'm confused..
In a different thread you said..
You said in that quote that the PCM puts out a 3V 5ms pulse.. not that it gets loaded down to 3v..
So are you saying that new evidence says 5V now?
Thanks for being patient, just trying to learn!
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Location: Edmonton
Posts: 551
RX-8 friend is now Offline::
The coil trigger wires come from the PCM. It puts out a +3V 5 mS pulse. To get true RPM you need to multiply by two, or add the pulse from both rotors (leading or trailing). If you are just detecting "engine run" (I suspect that is what that wire is for), you don't need to worry about that, just use one trigger wire. Put a diode in series and a resistor. Try 10K to start. If it doesn't trigger the unit you are installing, try dropping the resistance value by half. I wouldn't go any lower than that. We use 1N4148 diodes.
In a different thread you said..
You said in that quote that the PCM puts out a 3V 5ms pulse.. not that it gets loaded down to 3v..
So are you saying that new evidence says 5V now?
Thanks for being patient, just trying to learn!
Registered: Jul 2003
Location: Edmonton
Posts: 551
RX-8 friend is now Offline::
The coil trigger wires come from the PCM. It puts out a +3V 5 mS pulse. To get true RPM you need to multiply by two, or add the pulse from both rotors (leading or trailing). If you are just detecting "engine run" (I suspect that is what that wire is for), you don't need to worry about that, just use one trigger wire. Put a diode in series and a resistor. Try 10K to start. If it doesn't trigger the unit you are installing, try dropping the resistance value by half. I wouldn't go any lower than that. We use 1N4148 diodes.
06-28-2004, 10:22 PM
#12
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When I wrote that it was for a fellow without the CZ module, so he would see +3 V as it would be connected to the coils (which load it down to +3 from +5). With our box in, it's essentially disconnected from the coil (when the box is "on") so it measures +5 V, which makes sense, as the computer (PCM) runs on 5V.
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