[Diy_efi] Re: EMS inputs/output?

huw scourfield huw.scourfield at lineone.net
Thu Aug 1 22:38:19 GMT 2002


Yes sure, as I understand it the ecu has to force the mixture rich/lean in
order to read the "average" high and low voltage from the narrow band
lambda, this is because of the nature of the output curve of the sensor - it
is sometimes known as the "switching" sensor, and is only usefull around
lambda.
True open loop control is only achievable with a wideband sensor, however,
there is supposed to be an issue with the requirement of rich/lean mixture
for the cat to work.
    Huw
----- Original Message -----
From: "alex averbuch" <averchoob at hotmail.com>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, July 30, 2002 4:53 AM
Subject: [Diy_efi] Re: EMS inputs/output?


> Cheers Huw,
> What do you mean when you say that the "EMS constantly sends the mixture
> rich/lean"?
> Does the EMS actually tell the injectors to apply a rich mixture and then
a
> lean mixture, twice every second?!  That sounds primitive to say the
> least... wouldn't this method restrict the engine's performance to a
> considerably?
>
> Would you be able to explain, in more detail, why the EMS does this?
>
> Alex
>
> >
> >for lambda to work - (at least a narrow band sensor, a wideband is
>totally
> >different), the ecu constantly - at the rate of around once or twice a
> >second - sends the mixture rich/lean. The lambda sees this as a
> >square->wave
> >with varying mark-space ratio, the electronics then does some maths and
> >signals rich or lean and compensates accordingly. This compensation is
>an
> >adjustment of the "mapped" or pre-calculated fuelling - the open loop
> >fuelling. The reason for this is that a std lambda is a narrow band
> >instrument that only really works around stoichiometric, a wideband
>lambda
> >can work over a wider range and thus would not need the alternating
> > >mixture.
> >    Ping sensors can be very simple accoustic sensors, but to filter >out
> >unwanted noise a complicated dsp chip is usually used, this is normally
> >"gated" with the ignition signal to ascertain which cylinder is >pinging,
a
> >project on it's own I'd say!
> >    Dwell is the time the coil is charged by the battery, it is >normally
> >longer at cranking or low battery voltages and is controlled
> > >electronically
> >to prevent overheating the coil at low engine speeds.
> >    Huw
> >
>
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