For months I've been reading every thread, DIY, and diagram there is on vacuum issues. I finally did a bunch of testing today, and now I'm only more confused. I did find that my entire door locking system is completely in tact. The only reason it doesn't work is because it's not getting vacuum.

On my 83 300D, there are two vacuum lines branching off the main line to the brake booster. One is brown and goes to the ignition switch. The other goes into a 5-way branch that supplies the tranny (black), the HVAC (green), the door locks (yellow, split valve), another black that goes through the firewall and is capped off in the cabin (why? I have no idea), and finally a branch to the injection pump. Correct me if I'm wrong, but this is how I understand it so far.

When I start the engine, there is plenty of vacuum going to the brake booster (like 22-23" Hg). I also checked the vacuum just before it branches into the 5-way split and verified that there is still 22-23" Hg at this point. Now, with the engine still running, I check each destination point, one at a time, on the 5-way branch.

Green (HVAC) - no vacuum
Yellow (Door locks) - no vacuum
Black (Tranny) - no vacuum
Black (capped off in cabin) - no vacuum
Injection pump - full 22-23" Hg present with the other 4 capped off

So, this leads me to believe that my door locks are not working because they get no vacuum. This also makes me believe that my tranny shifts hard because it gets no vacuum either. Now, why is it that all my vacuum is being consumed at the injection pump?

I checked the connection for leaks, it all looks good. So, does this mean my injection pump is bad or there is a vacuum leak beyond it? What would I test beyond this point?

seabrighter,

Someplace U have a leak. Try removing one line at a time from the 5 way connector, plug the hole and see if the other lines now have vacuum. Then do same to 4 other lines. U should come across one that doesn't cause the othes to read zero vacuum and that will be the one to search for the leak.

P E H

The black line into the cabin is a vent line. It should not be capped.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

This is one of the things that confused me. How can you have an open vent line in a closed vacuum system? Isn't that basically the same as a LEAK? If I were to uncap this line, it would just be wide open and then how would the system have any vacuum at all?

This is exactly what I did, as I tried to describe above. It's the IP that's the culprit. What I don't know is how I check for leaks beyond the point where the IP connects to the 5 way branch. I don't know enough about the IP in terms how it uses the vacuum, and where in the IP system that vacuum could be leaking from so much that it draws all the vacuum from the 5-way system.

Where are the vacuum connections on the injection pump? Do U have a 617 engine?

Maybe yours is different than mine because its newer, but mine has a vacuum connection to the transmission vacuum valve and to the engine shut off . It there a tri- connector with a platic ring on one leg going to the vacuum valve?

P E H

Is it connected to a check valve under hood?

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83 SD

84 CD