[W126 Coupe] SEC Starting Failure After a Massive Downpour

[Richard Hogarth]

Fig-
You are asking a lot of good questions. It takes a huge amount of abuse to
get a coil to go bad. 
1)coil heat - A hot coil is not a good sign.  Because a coil is voltage
dependant device and not a current device, coils need an in line current
limiting resistor. Some coils have them built in and some use an external
resistor. Disconnect the coil, with an ohm meter test your old coil and then
the new one. See if they are the anywhere near the same. 

2)You only get the "speaker effect" when there is a lot of current flowing
through an inductive device. 
A speaker is low voltage but high current by comparison. 

3)Fluctuating timing: what is the mileage on the motor? If you have over
125K, you may get some spark wandering because of 'slop' or too much play in
the timing chain. This is caused by stretch in the chain and wear on the
plastic or phenolic tensioners.

4) More about wandering timeing - You may want to replace the timing
temperature sensor located in the intake manifold. The ignition system is
completely dependant on this sensor giving the ignition system correct
information. I have seen all kinds of eratic engine problems caused by this
sencsor going bad.
When this sensor begins to fail the engine may not start at all, timing may
wander, RPM may wander, RPM may surge, engine may 'misfire' eratically. Most
of these problems tend to occur once the engine approaches operating temp,
or as soon as the air idle valve goes out of high rpm start mode. (that
transition takes 11 to 15 seconds after the engine starts, according to the
manual. 

-Axlehead at bellsouth.net


-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com]
On Behalf Of a figment of the imagination
Sent: Saturday, August 20, 2005 9:25 AM
To: 'Mercedes Coupes Mailing Lists'
Subject: RE: [W126 Coupe] SEC Starting Failure After a Massive Downpour


Hi everyone:

I was going to rebuild my ignition module, component-by-component, but,
after calling around, I found a Bosch ignition module for $145 at Autozone
that
comes with a life-time warranty!!!!!!!!!!!!   ;) 

This completely beat out any deal I could find.  Our local dealer was asking
$825 for the ignition module and switching unit.  O'Reilly's was asking $292
with a one year warranty.  The next more affordable option was the salvage
price (in SoCal) of $125 plus one year
warranty.    Obviously, once the price is fair, who
really wants to buy "used", when it comes to an ignition module, eh?

So, in the end, the culprit was "NO SPARK!"   However,
it was not just the OpAmp in my ignition module that was bad, as my coil
also went bad.  Right now, I using an '85 380SE salvaged coil (same shape,
windings?) and am noticing some timing problems. This salvaged coil (I got
for free), is actually getting extremely hot and is probably "on its way
out", but just good enough to get me back on the road.  Today, I'm buying a
new coil and will be hopefully done with the aftermath of the Friday the
13th massive downpour.  

So, my remaining stupid question is can I get away with NOT doing a timing
job after replacing my ignition module + coil.  (I remember doing it in the
past, but "Yikes, the horror!")  My car right now (sans new coil) is giving
a "pitter, putter"
repetitive
noise on top of the normal smooth engine hum (which it had before these
replaced parts).  It sounds like missed timing, but my coil wire could be
pushing up and down slightly, changing the connectivity at the coil
terminal.

In other words, the inductive force from the coil to the coil wire may be
creating a "stereo-speaker" like effect of pulling and pushing the wire.  I
noticed on the used coil that the suction/grip of the coil wire is loose
than on my original tightly sealed coil + wire.  

Do coils generally get really hot?  I didn't think they did.  I know if they
get extremely hot, the inductive force is supposed to disengage the coil
wire off the coil.  This is why the coil wire isn't screwed onto the coil
and "pops off".

Thanks, everyone!

-figged out on my SEC that finally starts again!  Woo Hoo! :))

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