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As the EHA only has a limited effect on the overall A/F mixture, is there a value in percentage that the EHA can affect the mixture?



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Discussion Starter #62
As the EHA only has a limited effect on the overall A/F mixture, is there a value in percentage that the EHA can affect the mixture?
If by “limited“ you mean “small“, I recommend to reread the chapter “Basics“ in post 1. Towards the end of that chapter I said:
“From the above it may also become clear that the air/fuel mixture can not only be ‘micro-adjusted’ (to ‘λ ~ 1 +/- 0.02’) via EHA control, as often assumed, but also ‘macro-adjusted’ ...”

As I explained there in detail, the tiny fluctuating adjustments via EHA control to the (stoichiometric) Lambda range of ‘λ ~ 1 +/- 0.02’ equate, in case of non-ethanol fuel, to an air/fuel mass ratio range of about 14.4 - 15 (14.7 +/- 0.3). That’s a micro-adjustment range of +/- 2%.

But Lambda control is able to correct the air/fuel mass ratio back to that stoichiometric range via EHA control by (in chapter “Basics“ described) macro adjustments of up to about +20% (e.g. in case of a leaking CSV) or about -20% (e.g. in case of a vacuum leak).

During acceleration within the warm-up phase the mixture can be enriched via EHA control by more than 20%. During overrun shut-off the amount of injected fuel is reduced via EHA control by 100% (zero fuel).

H.D.
 

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Great, interesting.

So when the EHA is at "at rest"/volt-less the mixture should be close to 14.7 in "ideal" conditions? (Engine at idle, operating temp, etc.)

Does the KE also adjust for difference in altitude (barometric pressure) via the EHA, or only via the resulting change in mixture measured at the O2 sensor?

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Discussion Starter #64
... So when the EHA is at "at rest"/volt-less the mixture should be close to 14.7 in "ideal" conditions? (Engine at idle, operating temp, etc. ...
Yes … in case of non-ethanol fuel … or a little lower, like 14.2 - 14.3, which is the case after adjustment of the fluctuating EHA current to a mean value of about minus 0.6 mA, unless there‘s a fuel combustion affecting problem.

... Does the KE also adjust for difference in altitude (barometric pressure) via the EHA ...
Yes, it does … either directly & more precisely if the car is equipped with an altitude sensor, or indirectly & less precisely if it‘s not equipped with an altitude sensor.

In the latter case it‘s the o2 sensor alone that induces adjustments. It senses any difference in the ratio between the amount of residual oxygen in the exhaust gas and the amount of oxygen in the ambient air … thus including the effect that different altitudes have on that ratio.

Without any of these sensors (working), the engine would run richer at higher altitudes, because the air‘s lower mass per volume at higher altitudes causes a bigger stroke of the FD‘s control piston per mass of intake air, leading to richer air/fuel mixture. … With (correct) respective sensor input that is corrected via EHA control.

... or only via the resulting change in mixture measured at the O2 sensor? ...
As mentioned in post 51 (and contrary to common believe :wink_2:), o2 sensors can not really “measure the air/fuel mixture“. They generate voltage solely depending on the above-mentioned ratio between the amount of residual oxygen in the exhaust gas and the amount of oxygen in the ambient air … and that ratio depends not only on the air/fuel mixture, but on everything that has an effect on the fuel combustion !

Only if there are no fuel combustion affecting problems (and no holes in the exhaust pipe :wink_2:) a healthy o2 sensor‘s voltage of 450 mV is a reliable representative of stoichiometric air/fuel mass ratio. … That is usually overlooked but important to consider for proper troubleshooting !

H.D.
 
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