Air/Fuel mixture for 280SE 4.5 - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 07-29-2012, 04:17 PM Thread Starter
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Air/Fuel mixture for 280SE 4.5

So on the ECU is the air/fuel mixture control. After replacing a lot of vacuum lines, my car runs differently (which is to say, more rich now). The exhaust smells more like gasoline than anything else. I suspect I'm on the road to solving other, lingering issues as a result (yay me).

Anyone remember which way to turn the knob to lean out the mixture?
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post #2 of 2 (permalink) Old 07-29-2012, 09:34 PM
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Set MCU box in the middle of the clicks.
Then adjust the idle air screw,
If it increases idle speed then it is too rich,
If it doesn't then idle fuel is set.

Then I have leaned the MAP sensor (no more than 1/8 a turn at a time) so that the idle does not increase and achieves a solid low idle speed.

Then the MC|U will respond rich and lean with a few clicks.
This EFI really simulates the older MFI

At least that's the way I observed the response.

when the air screw is turned in, the mixture gets rich because the air is reduced the fuel stays constant.

Of course the timing is set perfect?
Vacuum diaphragm on distributor is good?

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