Funny how we learn things.... the GF's sport car did not finished the ride as planned... power dwindled, engine labored on inclines... so like a jeep I pulled over, lifted the hood and checked a few things... of course no tools... the engine came back to life after a 5min cooling period, but no overheating in 70 degrees weather, we had power for the next 2 miles... then again... pulled over... recheck... thinking now about the coil/electrical system... coil was hot, uncomfortable to the touch after 1sec... especially that it is not on top of the engine... 10 min wait... and repeat 4 times.
So to the point, how do we measure the coil resistance to compare it with its oem specs, the 450 manual tell you to replace with a known good one... but no specs listed, so a bit of a search let me find this from user jyuma, from https://www.benzworld.org/forums/r-c107 ... -coil.html
At the risk of boring the crap out of people... a transformer works by passing a current through the primary which results in the creation of a magnetic field. As the magnetic field builds (or collapses) the magnetic flux (lines of magnetism) cross the windings in the secondary which will create a voltage in the secondary. The amount of voltage in the secondary is a function of the ratio of turns in the primary to turns in the secondary. It is very much proportional to the degree that double the turns in the secondary will result in double the voltage in the secondary (but half the current). This effect of a current (voltage in motion) in the primary producing a magnetic field that then creates a voltage in the secondary is totally dependent upon the integrity of the coils involved. This is why simply DC resistance checks are all but useless, because the fact that the DC resistance between two different coils is the same doesn't tell you anything about the condition of the windings in the two coils.
Clear as mud?
and for the measurement, How to Measure Inductance of a Coil:
https://sciencing.com/measure-inductanc ... 46890.html
Inductors are sometimes wound by the user instead of bought. In such cases, the inductance would not be stamped on the side but instead may need to be found empirically. The best way to measure inductance for an inductor like a coil (solenoid) is to use an inductance bridge or meter. If you have neither, a more indirect way is to use an oscilloscope.
Connect a resistor of known resistance and the coil in series with the sine wave oscilloscope.
Turn on the oscilloscope and clamp the two clips of one voltmeter to the circuit on opposite sides of the coil to determine the voltage drop across the coil. Then do the same for the resistor with another voltmeter.
Set the frequency of the oscilloscope such that the voltage drop across the resistor and inductor are the same. Finding said frequency may be a matter of trial and error. At that frequency, the resistance of the resistor and the impedance of the inductor will be equal.
Set the resistor’s resistance and the inductor’s impedance equal to each other and solve for the inductance of the coil. Resistance = 2?fL, where \"f\" is the frequency of the oscilloscope and \"L\" is the coil’s inductance. The resistance of the resistor has not changed from the start; it is independent of the frequency. So \"L\" can be solved for by arithmetic.
Have fun... in the mean time I installed one the jeep spare coil and will be doing a drive test to confirm my hypothesis of a bad coil