How to test a coil ????
 

I'm trying to get my 1993 300e 2.8 fuel injection motor running correctly. Right now is misses and runs sluggish. Beyond wires, boots and plugs I'm concerned a coil might be bad. How do I test a coil.

Comments appreciated.

I'm sure this is a vague answer, but I believe you need to test the resistance using a multimeter. I'm sure there is a thread on here somewhere that contains proper procedures. Use the search. Also, I believe you would pretty much follow the same steps no matter what kind of car, so you might find luck just searching the internet.

Isn't that the way you test most electrical components? Verify that what goes in one side comes out the other?

Pretty much. Another way to do it (or at least isolate the problem) is this: when the car having the symptoms you describe, try misting some WD-40 on the suspect part. If the problem persists, move on. When you hit the failing part, it should help in running. This will work for wires, distributer caps, etc. If you CAN'T get the car to have the symptoms (often, they depend on the climate conditions, off and on, kind of a pain in the @$$ to diagnose), or suddenly it's running just fine, you can also mist water in the same fashion as described above. When you hit the problem part, it should recreat the symptoms.

Is that because there is broken insulation or something? The mist is causing it to short out?

It's usually moisture that would cause 99% of problems in these systems. Spraying WD-40 removes moisture (when its acting like poop); spraying water recreates a humid environment (when its acting nice). Humidity causes arcing (when there is a "leak" in the circuit). Arcing causes weaker sparks, cause the full energy just isn't there.

That makes sense. That's good to know. Thanks, Matt.