Emission Control System

[TEJOLX47]

Dear Pagoda lovers,

My car is a US 280 SL and therefore has an Emission Control System (ECC)
I struggled to understand its functioning over the time and have published a few tips in the Manual but recently asked for help to Duane Mariage who has a channel on YouTube for car electricity and electronic.
Duane decoded most of the ECC diagram in a film you can find on https://www.youtube.com/watch?v=-PzvtA03RGA
I hope you will enjoy.
Kind regards
Francisco

[Peter van Es]

Excellent explanation. I'll add this to the Tech Manual: https://www.sl113.org/wiki/Electrical/EmissionControlSystem

[jeffc280sl]

This truly is an excellent basic explanation of the emission control system.  I wish it was available 10 years ago when I was into figuring this stuff out myself. 

A couple of things come to mind.  The manual transmission version is different because it does not have a hydraulic transmission pressure sensor.  There are some switches located on the clutch and elsewhere to sense when the car is in a deacceleration mode. 

The speed relay box was not described in the presentation.  The wiring diagram does not describe the internal workings of this device.  The BBB has an explanation if you care to try and understand its function

I suspect most of the systems do not work today as designed.  Any number of failure points can render the system ineffective.  I have bypassed this system to simplify and improve performance.

 

[Benz Dr.]

If you disconnect the late USA emission system on a 280 SL you should also go back to the early ignition distributor ( 051 ) and the early throttle valve assembly. The late system employs a vacuum switch over valve and with that system not working you will only have about 10 degrees of distributor advance. A lack of power and heavy fuel consumption will be your results if you leave the late system disabled.

[jeffc280sl]

The Benz Dr is always thoughtful and correct.  I have switched to the 123 Ignition system on my SL with the factory throttle body

[dirkbalter]

If you disconnect the late USA emission system on a 280 SL you should also go back to the early ignition distributor ( 051 ) and the early throttle valve assembly. The late system employs a vacuum switch over valve and with that system not working you will only have about 10 degrees of distributor advance. A lack of power and heavy fuel consumption will be your results if you leave the late system disabled.

If have done exactly that on my 280 and it works like a champ. (051 distributor, 68 throttle body)

@jeffc280sl. When you say factory throttle body, are you using your original throttle body (70 ECC type) or an earlier throttle body with the 123?   

[Benz Dr.]

Actually, you can use whatever throttle body you want to but keep in mind that both the throttle body and distributor must be compatible. I have a VA throttle body on my engine to comply with my VA 300SE distributor.  The distributor didn't work so well until I figured out what was wrong with it. 

[dirkbalter]

If you use a 123 distributor with the original EEC throttle body, don’t you need the vacuum switch that turns off vacuum at rpm to work properly?
And, isn’t the vacuum switch part of the ECC system that you want to get rid of?

That’s where I got stuck and decided to switch to an earlier style throttle body.

I was reading up on the 123 system at that time but couldn’t really figure out if it can be programmed to operate original throttle body without the vacuum switch?

[Benz Dr.]

I'm not that familiar with 123 settings but regardless of that, you still need to match your throttle body to your distributor mode of action. The constant vacuum throttle body is designed to only work on the USA version emission controls. The most common throttle body is a VR version and that's the one I would look for.

[dirkbalter]

I'm not that familiar with 123 settings but regardless of that, you still need to match your throttle body to your distributor mode of action. The constant vacuum throttle body is designed to only work on the USA version emission controls. The most common throttle body is a VR version and that's the one I would look for.

Yes, I understand and agree.

[kampala]

Dirk

You are correct.  In order to use the 123 with a USA emissions system, you either need the two-way valve system working or you change/modify the throttle body to work with the 051 dizzy and set the 123 according to an 051.  This is what I did.

This said, others have just installed the 123 on these USA emissions models and not changed/modified the throttle body and just adjusted the linkage to compensate.  It seems to work but idle is typically higher. 

Another option is to use the programmable 123 and make a custom curve.  Have not done that.

[Benz Dr.]

The VR 051 distributor has 20 degrees of mechanical advance and 10 degrees of vacuum advance. Both are mechanical functions with one being controlled by flyweights and the other by a vacuum cell and a pull rod. These two movements will give you a full advance reading of 30 degrees and that can be fine tuned by turning the pull rod in or out. The actual advance curve can be changed a bit by altering the flyweight return spring pressure so that you can have an early or late advance curve.
Setting your ignition timing to 8 degrees BTDC at idle should give you 38 degrees of total advance. This is for the 051 distributor only. Other units will have difference advance curves and in some case, different functions.   

[dirkbalter]

Dan,
You advised and guided me on thru that a while back. Works great for me.

Oz,
Yes exactly. Since I could not get my valve to operate, I tried to find out if it’s possible to create or program a curve on the 123 that works without any vacuum input to the distributor. In other words, it only responds to RPM input.
Eventually I gave up, got a different throttle body and rebuild the 051 distributor from my 230. I am following these threads with interest because I will need another distributor soon.