[W126 Coupe] Re:SEC Starting Failure After a Massive Downpour

[Mister McGoo]

Hi Figment.

For an operational internal combustion engine to run you need three 
components: fuel, combustion air, and an ignition source.  It doesn't matter 
if you have a 2-cycle lawnmower or a Ferrari Dino.

If a functional engine won't start, you are missing (at least) one of those 
components.  You must first identify which of the components are missing 
before you can rationally begin to troubleshoot the cause.

Combustion Air:  We assume you have combustion air.  When you took off your 
air cleaner (TWO 10mm nuts or wing nuts... you DID take it off, right?) you 
surely would notice if, for example, a green garbage bag was stuffed into 
your intake horn, right?  So assume you have air.

Fuel:  You have confirmed that there is fuel in the tank.  You have 
confirmed that your fuel pump works, I believe you said by applying power 
directly to the fuel pump.  (it will hummm, vibrate or buzz)  You have NOT 
confirmed that fuel is reaching the fuel distributor / injectors / 
combustion cylinders.

Ignition source:  You have bought a new battery.  Your starting motor turns 
so you have power. You DON'T know if you have a spark at the spark plug.  I 
assume that while you are standing by the car with the air cleaner removed 
and a can of Starting Fluid in your hand, it would take approximately EIGHT 
SECONDS to squirt the fluid into the 4 inch diameter air intake opening in 
front of the fuel distributor and then turn the ignition key to try to start 
the car.  Have you done this?  You have not said that you have done this.

Please do this because it will almost certainly tell you if the problem is 
in the fuel system or the ignition system without buying any equipment or 
electrocuting anybody.

If the car fired up momentarily then you KNOW FOR MONEY-BACK GUARANTEED 100% 
SURE that you have spark, right?  So the problem is in the fuel delivery 
system.

IF the car DIDN'T fire up then you know you have no spark, right? Try again 
two or three times to cofirm this.  No go?  So the problem is in the 
ignition system.  Period!

You must determine this before you can rationally search for the problem.

What are possible causes?  Considering your description of the car starting 
briefly then dying, plus your description of things you have tried, the most 
common possibilities are:

1. IF you confirm the problem is in the Fuel System:   The Fuel Pump Relay.  
The relay is NOT the same as the 1983's on.  It is likely not the same as 
your 1974 280 either.  It is NOT under the fuse box; it is a plug-in insiide 
the fusebox (back outside corner, position "M").  It is fairly expensive but 
quite LIKELY you can fix it.

2. IF you confirm the problem is in the Ignition system:  The Ignition 
Module.  The module is held by three screws on the left wheel well of the 
engine compartment with one four prong plug and one single connector (the 
"fat" green wire to the base of the distributor).  There is an alternative 
ignition module made in Germany to replace the Bosch one at much less cost.  
(I have never tried one.)

BOTH the above components have been known to cause intermittent problems.  
Occasionally a faulty ignition module will allow your engine to start 
momentarily and then fail. The fuel pump relay will sometimes "fix" itself 
for a couple of weeks before it lets you down again (and it will).

BEAR IN MIND I AM SPEAKING OF MOST COMMON CAUSES... THERE ARE DOZENS OF 
OTHERS.

3. If you have confirmed that there IS fuel at the combustion chamber AND 
there IS ignition spark, and there IS combustion air, then you can assume 
that what you DON'T have is a functional engine.  This was the reason for 
the question for the (unlikely) circumstances when your engine appears to be 
turning over (but not firing) possibly faster than you remember before.  If 
on startup your engine timing chain jumped you may have wrecked your left 
bank valve train and have no compression on four cylinders.  Normally you 
would have heard a bang when it started and suddenly stopped.  But if this 
is your problem, even new set of prayer beads won't help.

Remember... try the fuel/fluid down the air throat first before buying any 
other parts, OK?


-Bellamy




>From: a figment of the imagination <figstir at yahoo.com>
>Reply-To: figstir at yahoo.com,Mercedes Coupes Mailing Lists 
><mbcoupes at mbcoupes.com>
>To: Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>
>Subject: Re: [W126 Coupe] SEC Starting Failure After a Massive Downpour
>Date: Tue, 16 Aug 2005 01:44:02 -0700 (PDT)
>
>Hi!  Thanks.
>
>I'll get the correct ignition module and coil from a
>salvage yard as a quick and dirty test.  This and the
>green wire should hopefully do it.
>
>The only solid evidence I have of any problem is that
>the area where the green wire attaches to the dizzy
>cap looks corroded with whitish (rusted aluminum) like
>residue.
>
>Are all "green wires" the same on the gas MBZs.  I
>seem to missing a silver cylinder on which the green
>wire attaches to and which sits inside the dizzy unit.
>
>-figment of a sleepless damp and drenched night
>
>
>
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