Interesting problem on my w126 euro 280se:

Recently looked at my pressure control regulator (aka warm-up regulator) and found that the intake manifold and atmospheric pressure connection was connected wrongly i.e. switched around.

Prior to this discovery, I had decent fuel consumption (6-7km/L) and a slight warm start difficulty. On testing the device with a vacuum gauge, I found that it leaked. At present I have not located a new or satisfactory used part, so it was put back but with the connection rectified.

The good news is that my warm start is now perfect. The bad news.....fuel consumption is down to 5km/L.

Looking at the mechanical fuel injection set-up, the pressure regulator looks to be one of the few devices which can alter the mixture and hence lambda. I am puzzled that a reversed vacuum/atmospheric connection should give a "good" mpg, and a correct connection, albeit with a leaking diaphragm, a bad mpg.

Will appreciate if any light can be shed on this.

My understanding is that a reversed connection connects the intake manifold pressure (vacuum) which displaces/sucks the diaphragm down and reduces the spring tension and hence reduce the control pressure leading to a rich mixture and higher consumption. Why is the reverse happening?

Thanks

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1983 w126 280SE - daily drive
1983 w123 200 - sold