[W126 Coupe] Problem 560

[Sharan Bains]

Hi Bellamy,

The fact that the engine died when you turned the headlights on first time 
round suggest there is some wrong interface between headlight wiring and the 
engine harness.

However, if you are wondering why no fuse blew, that's because there is no 
fuse on the engine loom, the big loom which links all CIS-KE and ignition 
EZL components. There is one on the headlights of course, but with the 
engine shutting down instantly, something on the engine management system 
blew quicker than the headlight fuse.

Now if there is some short circuit there on the engine harness, the first 
thing to usually blow is the fuel pump relay.

That may explain why it is not starting now and why it was able to start 
momentarily after the first stalling....maybe it ran on the fuel that was 
there in the pipelines and distributor, but with the fuel pump not working, 
it quickly died.

When you go and change the battery at the next visit, turn the ignition to 
position two and listen out for the fuel pumps. If no sound, then lit's 
probably the fuel pump relay gone. Double check with a 17mm spanner opening 
the main feed line on to the distributor and turning key to position two to 
see if fuel is gushing in or not.

How on earth such a interlink between headlights and engine harness can 
happen is usually during the fitment of aftermarket alarm systems, by an 
amateur installer. The fuel pump relay is a good place to splice into to 
prove the fuel immobilisation (good alarms usually immobilise starter and 
fuel pumps).....and some alarms allow headlights to be switched on using the 
remote fob, or to flash on arming/disarming.

So trying to wire in the two functions, it's easy to see how items that 
shouldn't communicate with each other end up doing so.

If you get it started, it's going to be a painful process of finding out 
what is happening with the headlight wiring.


talbir



>From: "Mister McGoo" <eelploot at hotmail.com>
>Reply-To: Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>
>To: mbcoupes at mbcoupes.com
>Subject: Re: [W126 Coupe] Problem 560
>Date: Sun, 30 Apr 2006 05:01:08 +0000
>
>
>
>Dick,
>
>I admit, I did not actually check the battery voltage before getting the 
>car started.  It had so little power that the interior light wouldn't even 
>glow.
>
>I would expect that even after just 15 minutes of running at 13.8 v 
>alternator output, there would be enough residual power in the battery to 
>get a flicker from the interior light.  But no.
>
>So I think Vance is right, the battery is total junk... not just one cell. 
>Therefore, the engine must have been running on the output of the 
>alternator alone.
>
>Considering that the power seats, windows, and heated seats worked also 
>when the engine was running, it is not reasonable that the lights alone 
>(components were tested one at a time) shut everything down.  Even more odd 
>is that the second (and final) time the engine stopped, nothing was "on".  
>The engine did not fade away, splutter, miss-fire, or make nasty noises.  
>It just stopped as would happen when turning the ignition off.
>
>-Bellamy 
>
>I must go back to recheck.  This time I hope to be able to install a new 
>battery.   
>
>
>
>
>
>
>From:  Dick Spellman <spell.yy at verizon.net>
>Reply-To:  Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>
>To:  Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>
>Subject:  Re: [W126 Coupe] Problem 560
>Date:  Sun, 30 Apr 2006 00:14:51 -0400
> >Hi Bellamy:
> >
> >I am no 560 expert either.  But, shouldn't that alternator be
> >charging north of 14 volts where the battery was dead?  I'd maybe
> >pull the regulator and see what's left on the carbon brushes if that
> >560 has 120k or more miles on the clock.
> >
> >Good luck.
> >
> >Dick
> >
> >Mister McGoo wrote:
> >
> >>All;
> >>  I was asked to view a problem 1988 560.  I have limited
>
> >>experience on anything newer than '85. (560)
> >>  I was asked to bring a fresh battery because the battery was
> >>dead, and I had about half an hour to determinbe what the problem
> >>was.  I wasn't successful.  I'm stumped.  And I ask for comments
> >>from 560 experts.
> >>  Symptoms:
> >>  The battery was flat dead.  I jumped the battery and the car
> >>started fine.  I disconnected the jumpers and it remained running.  
> >>The voltage at the [dead] battery was 13.8v. Obviously the
> >>alternator was working.  I warmed the engine up, tested the climate
> >>control, power seats, wipers, seat heaters, power windows, sunroof,
> >>power sunshade.....  all working
>fine.
> >>  The car had a 3/4 tank of fuel.  It was idling for about 15
> >>minutes.  I drove the car around the block, accellerating smartly
> >>when I could (the vehicle wasn't licenced so I couldn't go far).  
> >>Then I turned the headlights on and everything abruptly died.  (The
> >>owner said, "oh you turned the lights on.,  That's what happens;
> >>the alternator is shot.")  The battery still was dead.  I jumped it
> >>again, the engine started fine, and I disconnected the jumpers.  It
> >>continued to idle for about two minutes, then without anyone
> >>touching the car, the engine died abruptly again.  This time, when
> >>jumped, the engine would turn over but wouldn't fire at
>all.
> >>  The only possible abnormal condition is the idle speed was a bit
> >>high... around 1000rpm.
> >>  Any comments, suggestions?  -Bellamy
> >>
> >>
> >>------------------------------------------------------------------------
> >>
> >>The MB Coupes Website!
> >>W126 SEC Mailing List
> >>Postings remain property of MB Coupes, L.L.C.
> >>
> >The MB Coupes Website!
> >W126 SEC Mailing List
> >Postings remain property of MB Coupes, L.L.C.
>
>


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>Postings remain property of MB Coupes, L.L.C.