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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
500 Posts
Discussion Starter · #1 ·
Hello guys,

Could some one explain how does the Fuel Control Valve work? If I am going to adjust the Fuel and Air mixture, should I do the adjustment while power to the valve is disconnected? I mean, should the engine be running smoothly without the power to the valve then I connect it later. Another question, is this valve should work at acceleration only or not? Any ideas you submit are realy helful and thanks.


Premium Member
560SEC, 190E, Frontier, 240Z
1,334 Posts
I've messed with that valve extensively and have my fuel control system doing very well. I have a wideband O2 sensor installed so I know exactly what it is doing.

* Check your Idle Duty Cycle and set it to about 50%.
* Raise the RPM to 2500 and see what the Duty Cycle does.
* The Duty Cycle percentage needs to go down to the 20-30% range.
This indicates the EHA is over-richening a bit and the comupter is compensating just enough.
* If not, adjust the EHA (search that) right rich, left lean to get the desired result.

For me this results in ~12 air fuel ratio at full throttle.
A little richer than stock setup which works real good.

I've never had drivability problems too rich. But too lean don't go.

I have written a hideously exhaustive (and evidently annoying) thread elsewhere.

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