My 200K 1980 300SD has been parked for three years due to a vacuum pump failure. I have been driving my 420SEL in the meantime, but it is coming up on time for a timing chain replacement, and has developed a few other irritating habits such as a growing promiscuity with any old gasoline pump that it can find along the highway.

I had parked the 300 because I grew tired of having to manually shut off the engine, and was too busy at the time to attempt to make the needed repairs. Now that I want to go back to driving the diesel, I have a few issues. Though I have replaced the vacuum pump, and it is drawing (pulling?) 16 in/hg of vacuum, the engine still will not shut off at the key. Is there any sure way of testing the engine shut-off valve before I spend the money to buy a new one?

Also, the engine runs rough at idle with lots of vibration. Some of that may be related to leaks in the injector return hoses from their sitting and drying out, but I have ordered replacement hose, and will install it as soon as it arrives in a few days. So, that leads to another question: Whether or not I end up changing out the shut-off valve, and after replacing the injector return hoses, what should I do next if the rough idle continues?

Thanks in advance for any suggestions.

UPDATE UPDATE UPDATE UPDATE UPDATE UPDATE UPDATE UPDATE UPDATE UPDATE

It is now Friday afternoon. I had forgotten that she who must be obeyed had a Dr.'s appointment this morning, so I did not get to do any troubleshooting on the engine shut-off valve until after lunch. The good news is that, when I applied vacuum using my hand-held vac pump attached to the stub on the shut-off valve, the engine shut off as it should have ten times in a row. I was careful to watch the guage on the pump, and the engine was shutting off at between 8 and 10 in/Hg; mostly leaning to the lower range. I had reported that the engine vac pump was pulling 16 in/HG, so my conclusion was that there must be a vacuum leak somewhere in the system that is causing the shut-off valve to get less than the 8 to 10 in/Hg that worked it with the hand pump. The first things I checked were the relatively small check valves that attach at different legs of the 4-way rubber vacuum manifold. Both those check valves held good vacuum with no problem. I then attempted to test the other three check valves in the vacuum line leading to the brake booster. These consist of three larger check valves -- two in-line ones and one that comes off a tee and is an "elbow", 90-degree type. All of these check valves are attached to the thicker and much more rigid vacuum line, and I cannot, with reasonable pressure, get the lines off the ends of the check valves. There seems to be a great possibility that I could easily break one or more of those check valves if I get too enthusiastic about pulling them loose. Next question: How in blazes can I coax those check valves out of the hoses so that I can test them, AND, can anyone tell me of any other lines that I should check and the proper method of doing so? Thanks again for any help or suggestions.

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1980 300SD 146K miles.

Either use a Mity Vac to pull a vacuum on the shut off valve to see if it works, or get a piece of vacuum hose, put in on in place of the brown vacuum line and suck hard on the hose. Three good sucks should shut off the engine. If it doesn't the diaphragm in the shut off valve is probably bad.

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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

Testing for vacuum at the shut-off diaphragm would be the 1st step.

Then applying vacuum to that diaphragm w/ engine running should show where you have a problem.

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Mine shut off at 10 inHg with a mity-vac, but not with the key. I did have oil in the line to the ignition switch, replaced the shut off actuator, the engine stops with the key now.

16 inHg sounds low, check both forward nipples independently while the other is plugged off.

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83 SD

84 CD

Thanks for the replies, so far. If 16 in/hg is too low, is it a foregone conclusion that the pump I installed needs a rebuild or replacement? What would be the proper vacuum? I'll be out early tomorrow morning testing the vacuum line to the shut-off valve, the trying to close it using my hand-held vacuum pump. If the valve works okay using the vacuum from my hand-held pump, then I now know to look for oil in the line from the ignition switch; right?

Question two dealt with why I am getting rough idle, and I did mention that my injector return lines are very leaky. I will replace them as soon as the material arrives, but can anyone give me any other advice as to what I might be looking at if new return lines do not stop this problem. The engine idles at about 800RPM, but there is very significant vibration while sitting still. Once I engage the auto trans into D, the engine smooths out just fine.

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1980 300SD 146K miles.

One of the two nipples should give you ~15 inHg, so check the other nipple with that one plugged off.

There may be a check valve in the main vac line.

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83 SD

84 CD

Oil in the line typically happens because the diaphragm fails in the shut off valve. If it's working ok, there's no reason to look for oil in the line. You should look for leaks in the system if the shut off valve is working ok. Vacuum should be higher than 16 at sea level, more like 21.
Vacuum set up on a 79 SD is different than the 123's. There are two lines coming from the pump, not one like the 123's. Maybe the 80 SD's are similar. I had a leak at the small line rubber union at the pump.

Vibration could be worn motor mounts and engine shocks.

__________________
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

There is only one (1) line coming out of my vacuum pump, not two. I suppose the used pump that I just installed must be weak if the optimum vacuum should be 21 instead of 16 in/Hg, though I have read several posts that claim 10 in/Hg will work the shut-off valve okay. Should I try another vacuum pump R&R? Almost forgot to ask: Would a bad check valve at the vacuum pump cause my vacuum to be less than optimum?

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1980 300SD 146K miles.

Earlier today, I edited my original post to include the results of my shut-off valve testing. Please take a look at that original post, and let me know if you have any suggestions. Thanks.

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1980 300SD 146K miles.

What is missing in the testing I have read is what type of Vacuum (a reading from the Gauge) are you getting from the Brown Vacuum Tubing that hooks up to the Vacuum Shutoff on the Fuel Injection Pump. Sick that tube into your Mighty Vac and turn the key off and see how much Vacuum it pulls.

Find some way to connect up you Mighty Vac directly to your Vacuum Pump to see if there is enough Vacuum at the Pump.

Ther is also A Vacuum Shutoff Valve located on the Steering Colum Lock. That is what is actuated by the Key when you turn it. The 2 Vacuum Line connections could be having a problem or the Valve itself could be no good.

To test to see if it is a leak in your Door Locks or your Climate Control you need to plug off the Vacuum that goes to them. That will I believe leave you with only Vacuum going to your Shutoff and the Transmission Vacuum Valve.

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84 300D, 82 Volvo 244Gl Diesel

Two very common sources of vacuum leaks are the door lock system and the climate control system. Push the off button on the climate control and plug the yellow door lock system line at the firewall. (unplug the yellow line and use a golf tee in the line upstream towards the vacuum pump). If thf engine shuts down you'll know the problem is in one of those two systems. Don't mess with the check valves until you checked the vacuum in the other systems. The problem with a leak is typically a failed vacuum diaphragm 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

I have not read of the Injector Fuel Return Lines causing a rough Idle.

My first thought would be an Air Leak, if you still have that old style Hand Primer with the shiny Aluminum body on it that would be the first suspect. After that for a few dollars you can change the 2 Fuel inlet Hoses with 5/16" Fuel Hose from the local Auto Parts store (it is rated for Diesel Fuel); changing the Plastic Primary Filter will also eliminate it as a source of an Air leak.

After that I would be thinking Injectors and/or Valve adjustment.

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84 300D, 82 Volvo 244Gl Diesel