Moparts Tech Archive
Elec Topics
Elec Ignition question - How Work
Somebody raised this question on an Oz forum, and nobody could really answer it..so i figured I better try here...
How does the MP Elec ignition system actually work...I know what the componenets are, but how do the coil, Dist, ECU and ballast interact with each other to create a timed spark. I'm particularly interested in the ECU, what it does and how...
Hope someone has the patience to answer..Thanks
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As far as I know the Mopar ECU is basically an transistorized ignition system.
ELECTRONIC POINTS REPLACEMENTS:
Many times people refer to 'electronic ignition' and what they really mean is 'electronic points replacement'. These are typically the Ignitor, the Crane electronic points replacement [light trigger] and the Dale Manufacturing Chrysler conversion. These are the popular ones now and many other systems have graced the market over the years.
The design of these systems is to replace the points and use a electronic trigger to fire the coil. The electronic trigger can be a photo diode (Crane) or an inductive or Hall Effect magnetic trigger system (Ignitor & Dale). These systems will typically increase energy available to the spark plugs because of the more efficient triggering system and they are less prone to problems associated with points trigger. Some of the problems associated with points trigger are: rubbing block friction/wear causing 'shirking' point gap, point bounce, distributor shaft play causing inaccurate spark timing or misfire and points contact erosion since the points are a 'high current' switch. So replacing the points with an electronic points replacement system (transistorized switch) generally give a positive performance to most engines.
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what the above is saying is the transistor mounted on the heat sink on the Mopar (ecu, Ha!) is turned on by the magnetic pickup in the dizzy(as you guys call them), and discharges energy into the coil which upon reaching saturation will fire the spark plug.
It maybe that the Mopar performance system is a High Output system also. High Output (HO) transistorized systems use a power amplifier (Transistor) circuit to drive the coil with more power (amps). This is done by using the coil as an inductive storage device hereby increasing the coil output.
I can't say for sure if dwell can enter in this discussion, cause I just don't know. But with on/off times of power transistors (again the switch to "fire" the coil)in the tens to maybe hundreds of a milli-second, there isn't a whole lot of "dwell"
Hope this is of some help.
"Max"
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Ok Max, and thank...so to get this straight
The dist. tells the ECU to switch on and discharge current to the coil, which in turn sends a high voltage to the Dist, througt the rotor and to the spark plugs.
I d like to ident. what each wire in the ECU plug does..
The two wires to the Dist control the switching signal?
The wire to the coil + conveys the current?
The wire to the Ballast does what?
If I can get a handle on this last bit, I'm happy!
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The + wire supplies the power to the coil and the ECU grounds the negative part closing the circuit. This creates a magnetic field in the coil. The coil is what we call an autotransformer. When the ECU receives a signal from the magnetic pickup to fire a spark, the ECU OPENS the circuit, the magnetic field collapses and a spark is generated. A collapsing magnetic field creates a high reverse polarity voltage (energy).
The ballast resistor knocks the voltage down by a few volts to the coil (+) from 12 volts. The ballast resistor is bypassed during starting to produce a hotter spark. Run without the resistor and you will burn the coil up in a matter of minutes.
Simple actually.
Inside the distributor is the pickup and reluctor. The pickup has a magnetic field and a coil of wire. As the edges of the reluctor pass thru the pickup's magnetic field it generates a voltage in the coil, a small voltage and not enough to drive the coil.
This signal is sent to the ECU which uses it to control the coil. The ECU transforms the small pulse from the pick up into a signal of proper duration (this is where the dwell is created) to fire off the coil. It will generate a ground to the coil to allow it to charge up then remove the ground causing the spark.
The coil generates it's high voltage spark by collasping a magnetic field as described above.
The ballast resistor is not there to knock down voltage but to limit current thru the system. It's the excessive current that will burn out a coil. However, being that voltage = resistance times current any drop in current will affect voltage. But it is still the current that does the damage.
Timing the system is merely setting when the reluctor passes thru the pickup's magnetic field in relationship to the crankshaft's position in regards to TDC on #1 cylinder.
Steve
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