PeachParts Mercedes-Benz Forum - View Single Post - Spark Plugs: Resistor vs. Non-Resistor

oldtrucker · #59 11-16-2014, 01:03 PM

I am sorry, I don't mean to get that lenghty with my replies!

It just doesn't make technical sense, to use resistor plugs, if the vehicle wasn't designed for it.
In general the computer has not much to do with the sparks temperature (The noise can be filtered out, by design, at the computer end). If there are two resistor in series, the total resistance will be the sum of the two resistor.
In plain, if there is a restor wire (or other suppressor) in series installed and I add a plug with resistor, the total resistance is the sum of the two resistors. I could talk about impedance, but will refrain from that.
The computer may see, in very recent models, that the voltage across the electrode of the plug is less, but has really no way to adjust, e.g. add a few windings to the ignition coil to get the voltage higher up. Granted, some high performance coils have enough room to possibly compensate for the voltage drop. Perhaps they work on something like a electronically adjustable ignition coil, it's a Mercedes and the first owner will pay mega bucks for it. But in older vehicle, it will probably just trigger the CEL or indicate nothing but misfire. If there isn't the appropriate voltage, the spark is getting colder and in return may leave unburned components e.g. carbon deposits on the electrode. Also, higher levels of condensed water, acid's and more, contaminating your oil faster. The computer may try to adjust by running leaner at the cost of engine performance and possible damage, in some case. Also, misfire at idle may be observed.

As someone elsewhere stated in his story about Champion and NGK comparison, I believe that there was in fact an added resistor to blame for the misfire, although, misfire in an V8 or V12 requires lots of experience to detect just by ear or feel.

The myth about the resistor being better for computer controlled engines, comes simply from the RF (Electromagnetic field) produced by the spark and the abillity to supress it somewhat more. (also possible performance loss, all has to work together to be at top performance) All it does is, it knocks down the amplitude of the interference.

However, the statements, that resistor is better, are most likely from the marketing department (not engineering), since there is no "one size fits all", it is mostly BS.

Additional Theory:
A company needs to sell and with the demise of older cars on the road the tendency is to manufacture resistor plugs for the future and cease the older non-resistor plug production. Some people stated that it gets harder to find non-resistor plugs, meaning the manufaturing is at low quantities. With the newer ignition systems, designed for resitor plugs, the thought comes to mind, that marketing is directing you towards their new (full production) products.
Who gives a hoot if your car runs at top or will pass the smog test? This is the owners responsibility!
They may simply say "If you don't like it, buy a new car"