Everything went wrong all of the sudden!

[turkishcoffee]

Help me with my laundry list of issues. I've got a 78 240D that I like to keep in mint condition so this is very unusual. FWIW I'm pretty inexperienced working on cars and just learn as I go so go easy on me

1) Vacuum issue. A little while ago I got home and my engine wouldn't shut off. I noticed that with the driver's door unlocked it won't shut off, with the door locked everything works fine. All of the other doors can be locked or unlocked and it doesn't matter. Today I took a vacuum gauge and started checking everything. I pulled the 3 tubes out of the vacuum switch in the driver's door and tested each one. The yellow and green one on the front held no pressure, but the others did. I tested the valve itself and when I put the gauge on all 3 positions it would hold vacuum while locked and not at all while unlocked. Does that mean it's a bad switch? Also when I unlock it there is a hissing noise from the switch. OR, do I need to start tracking down a leak in that yellow and green tube?

2) Locks. They've been working fine until today. I tried to manually lock my driver's door and the tumbler feels jammed. I can lock and unlock all the doors fine with the plungers but it's almost like my key is wrong. Today I unlocked the trunk to get something out and when I closed it, the trunk locked and is now totally jammed. I can't get into the trunk at all. Is this related to the vacuum issue?

3) Fuel burn. Since I bought my car it has consistently gotten 26mpg. I noticed that my fuel gauge was down at 1/4 even though I just filled up and had only driven 180 miles. 12 MPG!! I figured it was the gauge but I put fuel in it and it actually took 15 gallons. My first thought was a leak but I don't see any fuel leaking. Second thought was the odometer but the trip odo seems to be working accurately. Did someone siphon fuel out of my car? If it went from 26 to 12 MPG there would surely be a change in smoke or power output right?

[Blazemaster]

Not sure if these are what your problems are, but here are 2 things on my 81 300d that I just took care of, and has to do with your symptoms.

1st are the vacuum lines under the hood that come out of the firewall near the oil filter canister. Whenever I change the oil in my car, or mess around in this area I always by accident pull the green hose loose, and the car wont shut off. The green one is a little loose on my car, so it is the one that gets pulled out easily.

2nd I just repaired a fuel leak in my car, because I noticed my gas mileage was very low and I also noticed a large pool of diesel on the ground when I came out from the grocery store. It took some searching to find the source, but eventually saw it was right in front of me. The fuel line that goes between each injector(the braided stuff) was leaking on the injector all the way in back, #5. I actually had some of this hose because I just replaced it on another 300d.

These are 2 things to easily check

[BenCohen-300TD]

Hi Turkish, I'm not one of the heavies on here but:

1) It sounds to me like you're on the right track with your vacuum trouble shooting. In order to decide if your problem lies in the switch, it sounds like you can just block off the switch, plug the lines going to it, and try to shut down the car. If you still have trouble shutting down the engine even when the switch is blocked off completely from the system and all the lines are stopped up, you probably need to keep exploring along your yellow and green lines. Otherwise, find a new switch.

2) I would try the simplest thing first with your locks and spray some dry-film lubricant in there. (unless someone on here strongly recommends against it for some reason.) I've had similar problems with key tumblers and this always fixes it. The trunk is probably something special. Not sure what to tell you there.

3) Simplest stuff first: are you driving anywhere unusual (like the city for the first time in this car) and are your tires all adequately inflated? That is a big jump in fuel economy but, as someone who drives both in the city frequently and on long trips on the highway (in an '79 NA 300TD) I'd say it is possible that it could just be environmental. My mileage is around 25 on the highway and much less around Brooklyn, maybe 17 or 18. Someone will also probably ask you if you've checked your air filter etc. The gas filler door should lock with the car doors, so it's unlikely someone got to your fuel.

Oh and Blazemaster has a good point, those injector return lines always pop off for one reason or another. It's a good place to check.

Hope there is something useful there,
Ben.

[Zacharias]

I won't address the vacuum stuff, except to say that it seems like you need to get hold of a vacuum tester (hand pump) and start troubleshooting.

On the outside door lock, try squirting in some silicone lube and then gently work the key back and forth.

The trunk lock should work with the key, regardless if whether the vacuum pod is functional. It may be jammed or just getting odd with age. Try thumping on the trunkid firmly, over the lock area, as you gently try to get the key to turn.

On the fuel mileage, two things come to mind. First that your odometer may be running slow. Second, you may have got a tank of especially skanky "winter" diesel. Or both.

It is likely you would smell any leak large enough to produce a huge drop in fuel economy.

[Junkman]

Ask Professor Google for a vacuum diagram for your car. You need to know what the lines go to. Vac starts at the vacuum pump and branches. You can disconnect and plug and/or use a hand pump on the individual circuits. Having the diagram will go a long way towards explaining which lines hold vacuum.

[charmalu]

This vacuum diagram might help you

W123 Vacuum InterLock Diagram

Your odometer might be slipping which is a common thing.

How to Repair Your Broken Odometer

I had a problem, I got the number wheesl off for the mielage. Had it apart several times
trying to keep it at the correct mileage.
Finally thought why not file off the flats on the shaft for the grey cogs?
Filed them off, pulled out the shaft. then move the wheels, slide in the shaft
and replace the cogs as you go.
The used a piece of wire smaller than the shaft, Removed a short piece of insulation with a wire stripper
then slipped it on the shaft. Been working for several years.
The shaft really does not spin.

When I installed the 150MPH spedo in the 240, this is what I had to do to reset it to the current mileage.




Remove your first aid kit, and under it is the fuel sending unit.
Use a 46mm or 1 13/16" socket to loosen the sender.
Lift it out and clean it, it is probably gunked up with crud.

Fuel Sender 85 300D- Cleaned (Pics)

Fuel Sender 85 300D- Cleaned (Pics)


Charlie

[Diesel911]

Are you useing the Key on the trunk lock?

Should be a vacuum diagram here: Door lock issue

Besides leaks winter fuel does not get the same milages.