Rantings of a maniacal Mercedes fan and DIY-er

Monday, July 9, 2012

More fun with troubleshooting the 300E

Alright, just an update on my situation here.  It has gotten worse, unfortunately :( the car now barely runs and can't really be taken anywhere.  There's a misfire at idle and low RPMs when you give it the beans, but once the revs go up it works fine (as stated before).  Since it is fairly consistent now I was able to get the duty cycle off of the car WHILE it was misfiring and all associated weirdness.  Interestingly, the DC never fluctuated beyond 45-55% while this was happening.  When it'd skip, it would go up to about 55% quickly and then come down.  Makes sense since there is then unburned fuel going through the system.  With this in mind, it is almost certainly electrical.  Since I've already gone over the cap, rotor, and wires today, that leaves me with bad plugs, bad coil, or bad ignition control module.  I have to dig out the EZL troubleshooting guide (I know I have it somewhere) and rule that out.  Not sure how to test the coil other than resistance for the different wire winds.

Also verified:
Wires are low resistance (1k ohms, printed on the terminals and verified as 1.1k though multimeter).  Again I have to verify with the manual as to the correct overall resistance spec but from searches on here, having 1kohm wires should necessitate resistor spark plugs, rather than the resistors being in the wire.  I don't want this to turn into a resistor v. non resistor post but I am just looking for the TOTAL spec from cap-end-terminal to the tip of the spark plug.  I am going to test this out before spending any more money (I am also planning on pulling each individual plug to make sure they're not fouled...the 2 I pulled today looked almost new, which is great since I replaced them 15k ago). 

I'm getting there...I'm trying not to throw any more parts on it until I can isolate the issue but everything just seems normal...