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  #1  
Old 09-19-2008, 11:03 PM
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Help on runnaway diesel (vacuum leak)

i just recently bought an 85' 300TD.
the car is fine and runs great, i started having problems with the car a couple of days ago, the car will not turn off when i take the key out of the ignition, i have to pop the hood and choke it off...and my door locks are not working either, i have to push down each one....
the previous owner said the vacuum line from the transmission was bad and leaked, i changed that line but im still having the same problem, i dont know how i can specifically find the leak.
Help would be Great..
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  #2  
Old 09-19-2008, 11:31 PM
compress ignite's Avatar
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Deceased Vacuum Pump (?)

Yeah,Wellllllllll, You'll get lotsa looks at your post with the "Tag Line" you're
using for a "Header".[Runaway Diesel is one that You Cannot Shut Off...
Hence the "Runaway" term ...result is usually Catastrophic]

It remains to be seen if anyone will reply (Kinda like you're crying "Wolf")

1.Mityvac ($26.00 @ Autozone) [Vacuum testing device]
2."Search" and "Advanced Search" portions of the Forum.
3.Better Yet ask if anyone has the Vacuum Diagram for your model so you
can begin testing.

Good Luck!
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  #3  
Old 09-20-2008, 01:04 AM
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Thanks alot
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  #4  
Old 09-20-2008, 01:13 AM
ForcedInduction
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CI gave great advice.

"Runaway" is where the engine revvs out of control, usually to destruction, on an external fuel source (engine oil for example) or injection system malfunction.

Your case is just a "Won't stop when it should" event. You can take your time to press the STOP lever and it will stop without any harm. A true runaway must have the airflow quickly blocked before the engine destroys itself.
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  #5  
Old 09-20-2008, 06:41 AM
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Marine Engineer (retired)
 
Join Date: Aug 2006
Location: West Virginia
Posts: 1,268
Arrow Runaway Diesels

Folks,

When using the term "Runaway Diesel" it is as stated ...a complete lack of control of the engine, and a continual acceleration until engine death .....generally this condition is caused by bad rings, or valve guides, and the engine consuming it's lube oil as fuel.....not a stuck FI Pump.....the FI Pump has an internal governor that should prevent any overspeeding of the engine.

SB
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  #6  
Old 09-20-2008, 01:59 PM
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Go to this site for step by step help. http://dieselgiant.com/mercedesvacuumtroubleshooting.htm
Make sure solid brown line has good vacumn, thats ign switch vac supply line and brown with blue line is shut off. Get some golf tees and plug off the door locks and HVAC vacumn lines, they are the most prone to have leaks, and it probably will turn off. Then you will have time to fix the problem leaks. Wife will never drive if she has to lift hood.
Good luck.
Phil
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  #7  
Old 09-20-2008, 04:45 PM
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Welcome to the site.
Now that I have been courteous and polite, welcome to the most easily searched problem on this website.
You have a vac leak robbing vacuum for your shutoff function. I commend you for listing your car and year. Take a golf tee and plug the vac line to the green line near brake booster going through firewall. {tee in the rubber connector to the green line} Let car run for a couple minutes and see if it shuts off. Do same with both the yellow and the yellow/gray.
These are the most common sources. {green line is to climate control vac. stuff/ yellow to door locks and yellow/gray to vac reservoir}
You need to invest in a Mityvac for future troubleshooting. If neither one of the above fixes your issue then you have a leak elsewhere I imagine, and the '85 models have about 3-4 times the vac lines of the other years.....
If either one of the above lines being plugged does resolve your shutoff issues you will still need the Mityvac for further troubleshooting. The brown line near the green and yellow goes to your ignition switch then from there to the injection pump. That is your shutoff "circuit"....
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  #8  
Old 09-20-2008, 09:22 PM
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Thanks for all the help and advise, i plan on trying to resolve this problem this week.
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  #9  
Old 09-20-2008, 11:17 PM
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Welcome

Hey Man,

Welcome to the site. I had the same problem on my '82 300 CD. Turned out to be a leaking boot on the lock vacuum actuator in the passenger door. One thing that helped track it down was that the car would shut down normally when driven for a while with the doors locked - the leak was on the un-locked side - Clued me in that the leak was in the locking system.

Be happy to help you track down the leak. Need to know how familiar you are with the vacuum system.

Others have suggested you search the site's archives for help. You'll find lots of good information there.

Later!
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  #10  
Old 09-21-2008, 12:19 AM
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Location: Newton NJ
Posts: 163
well runaway diesel got my attention!!!!

my first question is how are your brakes??? Is the pedal harder to push to get the car to stop? One or two leaking vacum elements usually wont cause the engine NOT to shut off.

Does your HVAC controls work? They too are controlled by vacum on this car. Everyone who owns a Mercedes of this vintage or older pretty much buys a mity vac as a matter of fact since they ALL have vacum issues. It is as handy a tool as a regular or philips head screw driver for these cars.

If your brakes are harder to push to get car to stop.. I'd start with the vacum pump as a potential problem. How many miles on your TD?

The modulator line going to the trans should not disable the engine shut off either. Welcome to the world of the Mercedes vacum!!!
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  #11  
Old 09-21-2008, 02:23 AM
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vacuum leak

Quote:
Originally Posted by ndnballa011 View Post
i just recently bought an 85' 300TD.
the car is fine and runs great, i started having problems with the car a couple of days ago, the car will not turn off when i take the key out of the ignition, i have to pop the hood and choke it off...and my door locks are not working either, i have to push down each one....
the previous owner said the vacuum line from the transmission was bad and leaked, i changed that line but im still having the same problem, i dont know how i can specifically find the leak.
Help would be Great..
I worked on a couple of diesels looking for vacuum leaks the hard way. Without a mityvac. Anyway both cars had bad shut off valves. Your problem could be this little guy attached to the ignition lock cylinder.
Have to take out instrument cluster to see it. If you are nimble enough, you can change it that way. I had to lower the steering columns.
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