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  #1  
Old 03-12-2012, 12:06 AM
Masterblaster426's Avatar
Masterblaster426
 
Join Date: Mar 2012
Location: Central Kentucky
Posts: 2
1977 240D hard to shut off.

Hi guys, Im sure this is a regular problem here, but I have not found a discussion on it in a quick search.
The car doesn't want to shut off.
I have found the best way to shut the motor off is to raise the rpms with a quick stab to the "gas" pedal and turn the key to the off position.
Otherwise, the motor will kinda "want" to shut off, but doesn't.
My first instinct is the ignition switch may need to be replaced.
The car has 180K on the crate motor. and 300K on the body.
My firend who has a 1983 300D has the same problem with his.
Ideas anyone?
Thanks ...and a great website!!
GCSS

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  #2  
Old 03-12-2012, 02:03 AM
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Location: Shelbyville, Tn
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Welcome to the forum.

Check your engine stop switch drivers side of the valve cover. If that works you probably have a vacuum issue with the ignition switched vacuum.
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  #3  
Old 03-12-2012, 03:15 AM
fashion victim immunizer
 
Join Date: Feb 2012
Location: oakland
Posts: 930
check the shut off valve on the back of the injection pump.

you'll need a mityvac or similar vacuum pump/tester. pull some vacuum on the pump, if the car shuts off then the valve is good and you'll need to trace the vacuum lines back until you find the leak. i dont remember exactly how much vacuum the valve needs to activate but I believe it's not a lot, i think 10 or 15" or something.

it's possible its the vacuum switch at the ignition. someone else would have to chime in on how to check that. my guess would be, turn the key to "off" and then apply vacuum to the supply line to the ignition vacuum switch. if it doesnt help or "slows" things down, it could be a break in the line or a bad ignition shutoff switch.

the vacuum circuit is should be easy to troubleshoot, because at least on my 81 300D, it's basically its own circuit. it should be supplied directly from the brake booster hose, and the line are brown. a brown line should go from the booster supply into the car through the firewall. another brown line should come out from the firewall and go to the shutoff valve on the back of the injection pump.
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Old 03-12-2012, 10:06 AM
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Join Date: Aug 2011
Location: Carolina
Posts: 1,542
If you perform the test described in the previous post and find that the shut off valve is good, You can test the switch by just putting your mighty vac in the same "circuit" but before the switch. I would guess that your problem is due to a bad shut off valve. I had to replace the original in my '78 just last December. its a bummer because ita take like 30 min to change it out but the part is gonna set ya back 'bout $100-$178. A bad Ignition Switch would probably be worse.

I would also insure for proper function of THE vacuum pump while you're at it. Its not impossible that you could have an "over all" vacuum problem. do you have problems with any of the other vacuum related functions with your car?
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  #5  
Old 03-12-2012, 02:06 PM
fashion victim immunizer
 
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Location: oakland
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excellent, i always forget the mityvac can be "tee"d into the line. that would definitely be the way to check the ignition valve
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  #6  
Old 03-12-2012, 09:22 PM
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Here's one..


eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
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  #7  
Old 03-13-2012, 12:17 AM
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Join Date: Dec 2011
Location: Honolulu, HI
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Quote:
Originally Posted by Masterblaster426 View Post
The car doesn't want to shut off.
This is actually a feature, not a problem.

It is merely living up to the anecdote that "Old Benzes won't die, they just keep on running..."


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