getting rid of emission control relays and wiring harness

[hdhardyb]

In my 1970 280 SL (manual transmission) the emission control stuff had been largely inactivated over the years: two-way valve removed and vacuum coming directly from throttle body.  However, the wiring harness and relays were still there with lots of useless cables hanging around (picture "ec_before"). I wanted to clean up the engine compartment and get rid of all those useless cables. At the same time I wanted to keep the fuel shutoff, like in a 1969 car.
 
It turns out that this is easy to do, just by cutting and re-connecting two wires. The pictures in the attachment show what I did. Happy to provide more details if this is of interest. The car is now wired exactly like a 1969 model with minimal emission control (just fuel shutoff, see Fig. 3.78 in Haynes). The fuel shutoff actually works better (somehow quicker) than before. This may be because the 1970 wiring through the additional relay causes some time delay.

Picture "ec_after" shows how it looks now, after some cleaning. The emission control harness and relays are stored in a safe place, just in case the next owner wants to re-install this stuff (which I doubt).  Quite happy with this little winter project!

[Leester]

That really tidies (tidys?) that area of the engine compartment up nicely. I'm a good ways off from that job (since it doesn't even have the engine in it) but I would be interested in which wires you cut and spliced so I can accomplish the same thing when I get there.

Lee

[Benz Dr.]

What are you using for a distributor? The original throttle body is designed to run at full vacuum all the time and is not regulated. If you have the original distributor installed you will only get 10 degrees of advance.

You would need to go to the 051 distributor and a vacuum retard throttle body to get full performance out of the engine.

[hdhardyb]

What are you using for a distributor? The original throttle body is designed to run at full vacuum all the time and is not regulated. If you have the original distributor installed you will only get 10 degrees of advance.

You would need to go to the 051 distributor and a vacuum retard throttle body to get full performance out of the engine.

Yes, exactly, the throttle body had been modified by Gernold Nisius to give vacuum when throttle is closed only, just like a '68-'69 model. This had been working very well with my original 062 distributor and now works even better with the 123 distributor (setting "8"). Getting the correct total advance of 30 degrees or so.


 

[hdhardyb]

That really tidies (tidys?) that area of the engine compartment up nicely. I'm a good ways off from that job (since it doesn't even have the engine in it) but I would be interested in which wires you cut and spliced so I can accomplish the same thing when I get there.

Lee

here are some more details. As I said before, this applies to the wiring in a 1970/71 manual transmission 280SL.

The emission control hangs on a wiring harness with four wires in it. First, remove the insulation in the area shown in the pictures. This will show the four wires, which I numbered 1 - 4:

1, 2: ground wires
3:  comes from throttle switch
4: +12V from fuse (red/black wire)

I numbered a fifth wire (5) which is grounded and goes to the transmission switch (3rd/4th gear).

- disconnect 1 and 2 from ground
- cut 3 and 4
- you can now remove the whole emission control wiring harness with the relays.

If you want to keep the fuel shutoff function alive, and wired exactly like in a '68/'69 model, proceed as follows:
- disconnect 5 from ground
- connect 5 with 4
- connect 3 with the fuel shutoff solenoid on the fuel injection pump

The second picture shows how it looks after these steps. The black wire on the left goes to the fuel shutoff solenoid.

Hope this is clear. It is really very easy.