[W126 Coupe] Hard starting diesel

[Mister McGoo]

Rich Sorry for the delay... I was not monitoring this... Yes, it sounds like the vacuum switch is the problem.  This switch is a small plunger type unit held onto the side of the ignition housing/ steering lock assembly with 2 screws.  Easiest to replace it if you remove the assembly (to say the least!).  To (maybe) see it, remove the instrument pod... should be two vacuum lines attached.  I believe there are instructions for removing the ignition assembly on this site. Picture: the assembly without the switch.  (All assembly castings are supplied with the diesel shut-off switch even the gas ones... blank of course.)  You can see the green cam inside the assembly that operates the switch plunger. -Bellamy


From: rsjaffe1 at msn.comTo: mbcoupes at mbcoupes.comDate: Thu, 29 Nov 2007 13:34:18 -0500Subject: Re: [W126 Coupe] Hard starting diesel




Bellamy,
 
You are 100% on target. I disconnected the brown vacuum line that goes into the tee above the rear of the injection pump, plugged it right back in and the car started immediately.  
 
Next question: how difficult is replacement of the vacuum switch at the back of the ignition switch?
 
Thanks,
 
Rich

----- Original Message ----- 
From: richard jaffe 
To: Mercedes Coupes Mailing Lists 
Sent: Tuesday, November 27, 2007 9:21 PM
Subject: Re: [W126 Coupe] Hard starting diesel


Bellamy,
 
Thanks for the info. I'll check that vacuum line tomorrow.
 
Rich

----- Original Message ----- 
From: Mister McGoo 
To: Mercedes Coupes Mailing Lists 
Sent: Monday, November 26, 2007 10:03 PM
Subject: Re: [W126 Coupe] Hard starting diesel
Rich; I read your original message again... you wrote that the engine won't start at all after being shut down. (as opposed to simply being hard to start).  Here's another possibility. Start the engine for a few minutes.  Shut it off and try to start it again.  If it won't start, look at the back of the diesel injector pump for a vacuum line.  From memory I believe it is brown.  Disconnect that vacuum line, reconnect it and try again.   >From your description your problem is quite likely a defective vacuum switch at the back of the ignition switch.  When you turn the "ignition" switch off, the vacuum closes off the fuel to the injector pump.   - Bellamy


From: rsjaffe1 at msn.comTo: mbcoupes at mbcoupes.comDate: Wed, 21 Nov 2007 22:15:02 -0500Subject: Re: [W126 Coupe] Hard starting diesel



Bellamy;
 
Yeah the extra oomph of a 603 would be nice, but I guess one wasn't available when the conversion happened. But it is kind of cool having a two ton tank of an SEC get 30 MPG.
 
I'll check the filters tomorrow. I don't smell any fuel in the engine bay. I wonder if there is some type of timer on the glow plug relay that isn't allowing it to function immediately after the car is shut off?
 
Thanks for the suggestions. Have a great Thanksgiving!
 
Rich

----- Original Message ----- 
From: Mister McGoo 
To: Mercedes Coupes Mailing Lists 
Sent: Wednesday, November 21, 2007 12:08 AM
Subject: Re: [W126 Coupe] Hard starting diesel
Rich; Hah!  One of those rare 300SDC models!  That's quite a conversion!  Too bad someone didn't use an '86 or '87 603 engine with greater power. As you know, most often a warm engine will start fine when a cold engine will not, indicating a glow plug problem.  You have the opposite problem?   Is there any smell of diesel present?  Check for leaks in injection lines or bypass hoses.  The problem may be a restriction in the air filter or the fuel filters.  Do you know when these were last changed?  If you suspect the air cleaner might be clogged, leave it out (or switch with your other car) and see if the problem is solved.  If you don't have any records, I'd change air and fuel filters as a starting point.  - Bellamy


From: rsjaffe1 at msn.comTo: MBCOUPES at MBCOUPES.COMDate: Mon, 19 Nov 2007 21:20:27 -0500Subject: [W126 Coupe] Hard starting diesel


Hello all,
 
I came across an 84 500 SEC that has had the V8 (broken timing belt) replaced with a 617 diesel motor and trans out of an 84 300 SD. If the car has been sitting a while, it starts fine. However, after shutting the car off, it does not want to start again when trying to restart after a few minutes. The starter turns the motor over but it will not fire.  But after sitting for a while, it starts just fine. Is this a problem with the glow plugs? Any ideas? I have not have this type of problem with my gasoline SEC or my 83 300 SD.
 
Thanks,
 
Rich Jaffe

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