280 SE EGR valve function and plumbing

[Feather535]

I'm working through the list of possible causes of high HC concentration on a California smog test, looking right now at the EGR valve. Testing the valve on the bench, the red vacuum port, which would be closest to the engine with the unit installed, holds vacuum but doesn't open the valve.  The blue (black?) port holds vacuum and opens the valve.  Is this the way it's supposed to work?

Also wondering about the plumbing.  The apparently non-functional red port is connected to a red vacuum line that appears to be connected to the distributor and the intake manifold; this line has about 10" of vacuum at idle.  The other port is connected to what looks like a thermo switch on the exhaust manifold that has another connection to a brownish vacuum line leading to the vacuum switch on the left fender beside the coil.  Does this sound correct?  It would be great to see a picture of the EGR installed with the vacuum lines.

[daantjie]

You will need to look at the vacuum diagram in the service manual for your model and year.  The anti smog crap evolved over the years so it's very much model specific.

Does your car have a smog pump?  There should also be a vacuum transducer valve with 4x connections on it.  At least on the V8's they had them.

From memory there should be a blue connection on the transducer which connects to a vacuum switch which in turn goes to the smog pump plumbing.  The EGR valve has 2x vacuum connections and I think they run to the transducer as well.

[Feather535]

You will need to look at the vacuum diagram in the service manual for your model and year.

Where is the vacuum diagram?  I thought I remembered seeing it, but now can't find it in the technical section. The link to emission control systems for this car https://handbook.w116.org/Engine/110/14-IntExhECS/ appears to be broken.

This car does have a smog pump and the transducer valve with 3 vacuum lines and an orange line from the exhaust manifold.

[daantjie]

To my knowledge the smog pump only really burns off the over rich mixture during startup and idle, whereafter the output of the pump is diverted to the catalytic converter.  That is the function of the thermo switch in the intake coolant section.

You might need to pull all the smog pump plumbing and check for carbon blockage.   I recall when I yanked mine it was all caked with black soot so it was not working anyway.  There are some bypass hoses as well as a gulp valve and such.  Unfortunately I think you will have to check it all as you are chasing small gains now.

Also check the charcoal canister plumbing.  I don't think it'll affect your readings but I'm not sure.  Fumes stored in the canister are drawn off into a connection on the throttle butterfly.   Here too mine was caked with soot.  Only way is to pull the throttle valve and clean out the bores.

But yes you must have the right vacuum diagram otherwise you will never get it right.  The one I have is for the 6.9 so it won't help you.

[daantjie]

I found this post on Benzworld, may help you a bit as it has some pics:

https://www.benzworld.org/threads/280se-egr-valve-vacuum-line-connection.1514178/

[UTn_boy]

Here are two different pictures.  One for Federal cars, and one for California cars.  I have no idea if your car has California emissions on it or if it has Federal emissions on it.  Nor do I know the year......all would be helpful in the future so as not to send you the wrong information.  The book these pictures are out of is from 1978.  If you have a different year, please say so so I can check that there are no differences and get the correct pictures to you.  Emissions often changed something every year. 

[Feather535]

Here are two different pictures.  One for Federal cars, and one for California cars.

Thanks for the pictures-super helpful.  For reference, I'm working on a California model 280SE, 1977.

[Feather535]

You might need to pull all the smog pump plumbing and check for carbon blockage.

Thanks for the suggestion.  I'll do that.

I expected the EGR valve might be caked with carbon, but it was clean and working as it should.  Also ruled out the charcoal can and evap system.  We'll see what happens with the smog pump. 

The challenge here is that I'm now chasing a number I can't measure and that doesn't affect how the car runs except at the extremes.

[rumb]

There is always "snake oil" to help pass emissions:

https://axleaddict.com/auto-repair/Tricks-to-Passing-a-Smog-Test

CRC makes an additive called "Guaranteed to Pass Emissions Test Formula."

[Alec300SD]

That is the function of the thermo switch in the intake coolant section.

Feather535:  Scale from the coolant can buildup on the thermo time sensor affecting the resistance adversely. Hope this helps.

[UTn_boy]

Here are two different pictures.  One for Federal cars, and one for California cars.

Thanks for the pictures-super helpful.  For reference, I'm working on a California model 280SE, 1977.

I'm glad you stated that it's a 1977.  1977 and 1978 California emission cars were not plumbed/set up the same.  Here is a picture from the 1977 manual for a 1977 280se with California emissions on it.