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...

Thursday, March 8, 2012

Intermittent stalling, RPM drop, misfiring...oh boy

So it wasn't the OVP.  I replaced that with a brand new unit and the problem persists.  To refresh, here's what has been plaguing my 300e. 

Very intermittently my car loses RPMs and stalls, but ONLY under load.  This first happened once in a parking lot after warming up, then again in the driveway.  Not too long afterwards, I parked the 300e for a bit since I didn't have a place for it, and it now does it about 40% of starts.  It is fine when cold, but after it warms up, the idle becomes rougher and as soon as you step on the gas a bit (still in park) it misfires and shakes badly up until about 2500 RPMs.  However, shift it into drive or reverse and it does the same misfiring but the RPMs drop until it stalls.  I thought it was the OVP since that is a very common replacement item, but no luck.  Also, during this time I found that my EHA valve (stands for electrohydraulic actuator) began to leak massively.  Again there was a glimmer of hope, but even after replacing it with a known good part, the problem persists.  Actually, I might as well just list all the stuff I've checked

- replaced ovp with new unit
- replaced cap and rotor, just inspected them again today to see if there was anything wacky there...cap had some usual corrosion on contact points but nothing out of the ordinary
- replaced wires, checked again for arcing today and nothing
- replaced EHA (was leaking wildly, had to be done anyways)
- checked engine temp sensor, appears to be fine
- checked the flywheel crank sensor (which goes to EZL), came out to 880 ohms, which is well within spec
- replaced O2 sensor
- fuel pump is always on during this so that rules out FPR
- replaced spark plugs (proper style - ordered from here)
- checked vacuum connections, seems fine
- duty cycle (checked via X11 diagnostic port) remained within 47-51%, which is very good--Lambda tower does not need adjustment.

Really not sure where I am heading from here.  I think I am going to replace all of the vacuum lines that I can find and hopefully fix any leak that might exist.  Stay tuned....