Hi everyone,

On my 82 300CDT the ignition switch was bad, so to keep the car original I bought one from the dealership...120.00 ouch, ok, I read every thread, got pictures, and voila it is changed works great, no more sticking, but uh one problem...now the car is taking 5-10 seconds to cut off HELP!!! I promise I was fixing something that needed to be fixed! I was'nt doing my, "Gee that looks like something that can take a wrench" routine So what did I touch.?
Also lately (last week to 10 days) the oil pressure guage goes straight to 3 and stays there. All advice and answers greatly appreciated. Also re: the 91 SDL it's a no go Wifee really did not like the color, and the dealer said he must get 10K.

Thanks,

JOe

Did you change the actual ignition switch, or just the locking cylinder?

Just the Cylinder Tango.

There is a vacuum line near the back of the switch that controls engine shutdown. Maybe it was disturbed. Must not be completely off or you would not be able to shut down at all with the ignition switch. Or maybe you have a vacuum leak elsewhere.

Would vaccum cause a problem with the oil guage?
It was operating normally, now it just pegs 3 at start-up and stays there?
Do I have a vac gremlin ya think?

Here is a picture of the ignition switch. See the two vacuum connections.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog2.mercedesshop.com/&cookieid=1DX0L34WQ1DZ1AFT4X&year=1982&make=MB&model=300-DT-001&category=M&part=Ignition+Lock+Assembly

The oil pressure gauge is not affected by vacuum. So the oil pressure reads 3.0 at all rpm's? Meaning that is does not drop at idle?

Nope, worries me... for a while(couple days) it was doing it
and it would jump down flutter at 1.5-2, then upon acceleration hit 3 and stick, it acted mechanical, not fluid for those couple days, now I hit the key, when it turns over up to three and stick?

Joe

Cooler ambient temps will cause higher initial oil pressure, but it should drop at idle once the engine has run long enough to warm the oil.

Do I have a vaccum leak?

If your oil pressure sending unit is bad, the needle will jump to the top and stay there as soon as you turn the ignition switch, even if the engine is not running. Otherwise, it will go up to the top at first, but will go down to the halfway mark with the engine idling at a traffic light, for example, once the engine has warmed up.

This is what my 90 300D did. I replaced the sending unit and now it works fine.

An incorrect connection or a crossed wire to the ignition switch might make the Oil Pressure gauge malfunction.

When a MB Diesel does not shut off, this is usually due to a vacuum line being pulled off or leaking. This is easy to do when you change the oil filter.

Check all the vacuum connections.

It is possible that the oil pressure sending unit has failed coincidentally, but before you buy another one (they are not expensive and connect with just one bolt and one wire), check the wires on the ignition switch.

Good luck!

__________________
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1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

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The shut down problem is likely vacuum related. There is a vacuum actuated shut-off unit on the back of the injection pump. Vacuum is applied to the unit when the ignition switch is positioned to "off." A vacuum valve on the ignition switch assembly opens to route the vacuum to the shut-off unit. If you have a vacuum tester, try applying vacuum directly to the shut-off unit. (It has a single vacuum line routed to it. The unit is a metal cylinder which protrudes from the very back of the injection pump. Not to be confused with the plastic vacuum valve on the top rear of the IP which has two vacuum connections.) If the engine shuts down with vacuum applied to the shut-off unit, you have a vacuum leak somewhere. If the engine does not shut down, then the shut-off unit is defective. Odds significantly favor a vacuum leak. Since you just worked on the ignition switch, I would start by checking the vacuum line connections there. Another common cause of vacuum leaks is the door locks. See if the engine shuts down faster with the doors locked versus unlocked. (I once had a bad door lock actuator and my engine would only shut down with the doors locked.) If you have done any other work under the hood (ie: oil change) which might have knocked a vacuum line loose, that would be worth investigating. Or you could have knocked a line off a vent flap actuator while removing/installing the under-dash panels.

The '82 models use a mechanical oil pressure gauge. An oil line routes oil directly to the gauge. No electricity involved.

Guys thanks for all your help, it appears the vaccum may have just been to discharged to work .
Drove around the block, everything fine there. Oil pressure guage dif story, will work on that and get back with you, first I will do a search to see what I can find, and check out the sending unit.

Thanks to All

Joe