'83 240D - Loss of Engine Power After 3/2 Valve Replacement
 

Hello to everyone... first post here.

I recently acquired an '83 240D with a manual 4-speed (270K miles) as a hobby restoration project. The car starts right up and generally drives well. One issue that I wanted to tackle right away was the vacuum leak that was affecting the door locks. Testing the system, I found that all the parts of the locking system were good, as well as the vacuum pump (24 mmHg). I traced the leak to the 3/2 valve on top of the engine, and got a new valve to replace the worn out one.

I replaced the valve and re-connected the lines just as they had been before (photo attached). The car started right up, idled as it should, and the locks worked great. However...


the car now has a top speed of about 15 miles per hour. :eek: Just no power whatsoever. Unplugging the vacuum line from the 3/2 valve brings back the power, but I lose the locking function again. Obviously, if I then cap that disconnected line, the locks come back, and I lose power again. I don't really know what is causing the loss of power. I guess I'm looking for suggestions on a good place to start to diagnose the issue. :confused: It's my first foray into the MB universe, so I'm a bit of a noob.


Thank you in advance for any guidance.

Plug the line going to the EGR and your problem will disappear. The EGR is on the bottom of the intake.

I had the same issue on my '81 240D. It has no EGR. I had crossed the brown vacuum tubes to the valve on the ignition switch. Running vacuum backwards through the valve on the way to the shutoff on the injection pump. It did not seal that way and was feeding just enough vacuum to the shutoff to cause this.

Thanks for your replies, but no joy with either of these, sorry to say. Plugging the EGR line had no noticeable effect, and swapping the brown lines made it so I couldn't stop my engine until I switched them back. :eek:



I did notice that disconnecting and plugging what appears to be the "altitude fuel adjuster" line (see attached pic) *seems* to bring back the power... I haven't driven it yet, but the engine seems to rev up like it originally did before the valve change) and the locks work. Is it OK to drive it this way? I'm guessing it is, but want to make sure.

The fuel adjuster port should be open to atmosphere. Vacuum is not meant to be applied there. That port gets left open.

I would check the routing of all your vacuum lines overall since that 3 way you capped is missing its appropriate user.

"https://blog.*******.com/mercedes-w123-240d-vacuum-overview" seems to have good images of a starting off point. There are lots of variations and people fiddle with things all the time. Try to see what you have and what you want to get rid of.

Great info; thank you. I had no idea that port was supposed to be left open in the first place. It certainly makes me wonder about the rest of the routing. Time for me to jump in and do some more research.