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  #1  
Old 08-28-2009, 12:56 AM
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run on wierdness

Hello,
I have been on this forum only occaissionally. Wonder if I could get some advice tonight.
Yesterday I couldn't get my 1979 300SD to shut off. After turning and removing the ignition key she just kept going. I was able to use the emergency shutoff by briefly over-revving then pushing the lever to finally kill the engine. The manual says this is the fuel solenoid malfunctioning. A friend suggested there might also be an issue with the vacumn pump. Can someone tell me how I know which before I start diagnosing by parts replacement?
TIA

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Old 08-28-2009, 12:58 AM
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This is a common problem. You have a vacuum leak. Get a vacuum tester pump, search for a map of your vacuum lines and start diagnosing. Start at the shutoff valve on the IP.
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Old 08-28-2009, 01:04 AM
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Yes. Pull the vacuum line off the shutoff valve with the key off and the engine still running. If you get plenty of suction at that line, then you know it's the shutoff valve. In the very likely event that you don't get strong suction at that line (21" Hg or thereabout if you have a gauge), then you should check at the vacuum pump. In the also very likely event that you get plenty of vacuum there, you then know that you have a leak in the system and can start looking for it.
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Old 08-28-2009, 01:34 AM
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There is no fuel solenoid. The shut off is vacuum actuated. Pull off the brown vacuum line from the shut off valve on the back of the injection back between the pump and the oil filter housing. Put a few feet of rubber vacuum hose in its place. With the engine running, suck on the hose hard two or three times. If the engine shuts off, the shut off valve itself is working fine and the problem is elsewhere in the vacuum system. If the engine doesn't stop, the shut off valve is bad and needs to be replaced.
If the shut off valve is fine, you'll have to troubleshoot the vacuum system to figure out why adequate vacuum is not getting to it when you shut off the key.
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Old 08-28-2009, 02:28 AM
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thanks for all the replies. I'll start going after vacumn this weekend. If its not the vacumn pump, will I just be replacing old hoses to fix the problem?
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Old 08-28-2009, 04:02 AM
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Quote:
Originally Posted by greendream View Post
thanks for all the replies. I'll start going after vacumn this weekend. If its not the vacumn pump, will I just be replacing old hoses to fix the problem?
If it is a bad shutoff valve as mentioned above, you need to be certain you follow the right procedure to replace to avoid a run away engine. Go to the DIY section and do a search for pictures and instruction details.
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  #7  
Old 08-28-2009, 11:28 AM
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There are virtually unlimited possibilities for vacuum leaks. Vacuum lines themselves rarely fail. Fittings and diaphragms fail pretty frequently. If you still have power brakes, your vacuum pump is ok.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 08-28-2009, 11:39 AM
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Yes, I finally had to disable the door locks on the CD.
If there is any oil in the vac line, it's time for a new shut off actuator, even if it does shut the engine down.
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Old 08-28-2009, 12:08 PM
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Do yourself a favor and get a Mity-Vac or similar hand-held vacuum pump. Then starting at the vacuum pump - which should pull about 21"-22" Hg - work your way back through the system. I am currently going through this process myself. The vacuum pump is good as is the fuel shut-off valve (I can pull vacuum - I think it was only about 7 or 8" HG - on it and get the engine to shut down. This makes me believe that my ignition switch, but haven't had time to chase it down yet. My locks are also problematic, so could be a related issue. If I get the chance I will do more digging and post my results. Good luck!
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Old 08-28-2009, 12:55 PM
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If you think the problem is in the door lock circuit, disconnect the yellow vacuum line near the firewall on the left side under the hood and plug the fitting with a golf tee. I disconnects the whole locking circuit from the system. If the car shuts off fine when you do that, you've isolated the problem to the door lock system somewhere.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #11  
Old 08-28-2009, 04:12 PM
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Quote:
Originally Posted by kerry View Post
If you think the problem is in the door lock circuit, disconnect the yellow vacuum line near the firewall on the left side under the hood and plug the fitting with a golf tee. I disconnects the whole locking circuit from the system. If the car shuts off fine when you do that, you've isolated the problem to the door lock system somewhere.
I tried that on mine, but it didn't cure the no-shut-off problem. thinking mine is in the ignition switch, but need to investigate more.
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  #12  
Old 08-29-2009, 04:21 AM
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check the shutoff valve. pull a vacuum on it and see if it holds it. if no, replace it.
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Old 08-31-2009, 02:07 AM
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Quote:
Originally Posted by Skippy View Post
Yes. Pull the vacuum line off the shutoff valve with the key off and the engine still running. If you get plenty of suction at that line, then you know it's the shutoff valve. In the very likely event that you don't get strong suction at that line (21" Hg or thereabout if you have a gauge), then you should check at the vacuum pump. In the also very likely event that you get plenty of vacuum there, you then know that you have a leak in the system and can start looking for it.

I followed this instruction and it worked like a charm. Now I can stop the car with my vacumn gauge hooked up to the vac line i ran through the firewall. I just need to trouble shoot the system till I find the problem.

Question: the brakes were acting a little strange. Could this be a sign the vacumn pump is on its way out?

Is it possible to overhaul the whole vacumn system, just replace all the diaphrams etc?

thanks for the help.

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