Need Help Identifying A Vacuum Line

[Apodman]

I'm sure I have a vac leak on the 280E(M110) given the rough engine running at idle only when fully warmed up. I'm not ready to invest in a MityVac, though I acknowledge I may have to.

The main vacuum line to the brake booster looks good, though I don't know how functional the in-line check valve is.

What is very obvious are cracks on the rubber joint coupler at the end of the medium-sized orange vac hose that comes off the exhaust manifold. It ends at what appears to be a vac distribution point. This is a short cylindical box next to the distributor, where smaller lines are attached to the same "box" as the orange medium-sized line. The smaller lines look like door lock lines and heater control lines.

What is this orange line, what is this distribution box and could the cracks in the rubber coupler be enough to create poor idling characteristics? My Hanes manual is not the least bit helpful with this.

Thanks, Alex

[ctaylor738]

The orange line is the vacuum supply to the EGR valve. Above a certain temperature and RPM, the vacuum opens the valve and allows exhaust gas to flow into the intake manifold. This needs to work right for the engine to run well.

The valve needs to have good vacuum to work right.

If your EGR valve is sticking open at idle, then that will cause a large vacuum loss at idle. Similarly, if the control mechanism is not working right, then it may be allowing the valve to open at idle.

What year is your 280E, and what color is the data plate on the radiator crossmember, because the setup and testing procedures changes in 1980.

[Apodman]

She a 1978, but built in September of '77. The plate is body color, if this is the one you're speaking of.

So what you're saying is the EGR valve is what I am describing as a distribution box? "This is a short cylindical box next to the distributor, where smaller lines are attached to the same "box" as the orange medium-sized line."

In the short term, I can seal the rubber coupling union. I'll order a replacement today or tomoroow. Do you have a better name for that rubber piece?

Thanks for your patient explanation.

Alex

[ctaylor738]

OK - looking at the diagram for a 1977-79. What you may be looking at is the "vacuum transducer" which is sort of the hub of the vacuum part of the emissions system. You should see the following lines:

Black - to thermovalve via checkvalve
White - to upper intake manifold
Brown - to exhaust manifold
Orange - to EGR valve (sits on the exhaust manifold)

I am getting this out of the M110 engine manual, which I only have in hard copy. If you want me to fax you the test procedures, send me an email with your fax number - ctaylor738@aol.com.

[Apodman]

Chuck,

Thanks for your offer. I can get access to a MB M110 Engine Manual this weekend(brother-in-law's), so I'll take a look then. Once I seal-up the connecting piece, I'll know if that was the root of the rough-idle problem. I'll let you know.

Alex

[autozen]

You've spent all that money for that stable of cars you've listed and you can't spring 35 bucks for one of the most valuable tools in a professional mechanic's tool box? I'm confused.

Peter