I'm glad someone started a continuation thread about this subject. I think that things might be getting off track at bit. See if you agree.
I guess I may have intrepreted the original thread a bit differently. What I read was;
"Bad wires, cap, rotor and/or wrong spark plugs can wreck your ignition module".
I agree that there is a lot of subjective information about using different type of plugs in different engines. I have my own opinions based on my personal experiences with different ignition components. I agree it does make a difference what you use where. But the original thread was not about that. It was about;
Quote:
|
"Bad wires, cap, rotor and/or wrong spark plugs can wreck your ignition module".
|
I have a lot of experience of what happens in the ignition system of these cars on a microsecond level. Without getting into all the techno mumbo jumbo the bottom line for me is this;
If "Bad wires, cap, rotor and/or wrong spark plugs can wreck your ignition module" then you have one crappy ignition system. The engineer who designed this thing should undergo appropriate punishment.
It is my opinion that the ignition systems in these cars is another great example of robust German engineering just like the rest of the car. I dont believe the statement ""Bad wires, cap, rotor and/or wrong spark plugs can wreck your ignition module". If it were true then ignition modules would be dropping like raindrops in a hurricane. This is not the case. Just pull the high voltage wire off the coil - that certainly represents total failure of everything that comes after it. The ignition control module does not break. If it did, the designer of the ignition module, you would be forced to make the module survive all sorts of failures in the other components.
What can go wrong with the various components? Lets take a few examples from an electrical perspective and assuming everything else is OK mechanically.
1. Spark plugs;
- Leakage resistance from tip to ground due to carbon deposits - Result - weak spark.
- Resistor has high resistance - Result - weak spark.
- Resistor has low resistance - Result - stronger spark.
- Resistor has open condition (Almost impossible to occur) - Result - no spark
2. Ignition wires (resistive type)
- Wires leaks or arcs current to ground (insulation failure) - Result - weak spark.
- Wires have low resistance (Almost impossible to occur) - Stronger spark.
- Wires have high resistance (carbon conductor failure) - Result - weak spark.
3. Distributor Cap.
- Cap leaks or arcs current to ground - Result - weak spark.
- Cap has corrosion on terminals - Result - weak spark.
- Cap leaks current between the various terminals - Result - weak spark & misfires
4. Rotor
- Rotor leaks or arcs current to ground - Result - weak spark.
- Rotor has corrosion on surfaces - Result - weak spark.
None of the problems listed above, (I think I got them all) has any impact to on the ignition control module. The module is not affected in any way by these conditions with the exception of "open circuit secondary". The one component that has any possible chance to damage the ignition control module is the ignition coil itself. The coil has the following failure modes;
- Coil primary is open - Result no spark, no primary current
- Coil leaks or arcs current to ground - Result - weak spark. Same as leaking wires.
- Coil has internal shorts in the windings - Result varies depending where the short occurs.
Possibilities include Weak spark and or high primary current.
It is the shorted winding scenario that represents the most danger to the ignition control module. High current resulting from a shorted primary will the stress the ignition control module switch and produce a lot of heat and failure. But ---- if the control module is properly designed it should protect itself from that condition. I do not know if the MB ICM's have this feature or not. The protection feature known as "current limiting" and is often designed into control electronics to make them more robust and resistant to failure.
Now when the coil output terminal (High Voltage) is not connected to any load (the wire removed) the voltage goes very high. Much higher than it does when it is connected to the distributor. The voltage will find a path to ground if it can. This condition places the most stress on the coil and to some extent the ICM. The ICM has an internal voltage clamp which prevents this over voltage condition on the secondary of the coil which is reflected to the primary from damaging the switching element. They are designed to be able to withstand "open circuit secondary" conditions.
The issue of resistance vs non-resistance components has such a small impact on the current and voltage waveforms that it is difficult to see. The resistance was put into ignition circuits in the early days to prevent noise in the AM radios of the day. It really has nothing to do with the arcing and sparking of the plugs.
So thats my opinion. And thats why I don't believe that the resistance of plugs / wires or rotors and distributors that leak or arc can cause damage to the ignition control module. Now for which brand / type make the engine run best - thats another chapter.
I am still waiting for someone to produce a copy of the TSB mentioned in the original thread.