"closed loop" is just using feedback from the O2 sensor to continually
adjust input fuel/air mix to optimum. Fine tuning on the run.
"open loop" is just "dump enough gas in to make it run" for a wide range of
conditions. There's no correctional feedback.
Without the sensor measuring at the END of the combustion process,it's not
the "loop" is; input..combustion..output..*measure output*..make CORRECTION
Without the correction,there's no "loop",it's an "open-ended" process.
The closure is the feedback corrections.
Think of the AC and thermostat in your home; you set a temp,and the AC
runs,cools the room,and the TS measures what the room temp is,and when it
reaches your setpoint,it shuts off the AC,and cycles. That's "closed
"Open loop" would be you turning on the AC and running it for 10 minutes
every hour,say on a timer.
The room MAY be close to where you want it,perhaps not.That would depend on
how hot the room was to begin,and how how it is outside.
There's no measurement and feedback control.
Thanks. I think I see now. That since the main output of the ECU is the
injector duration, then the main input (to have a true feedback
"closed" loop) is a sensor that measures the effects of combustion (O2
So I take it you mean that based on the other sensors (MAP, TA, TPS,
PA), the ECU does no fine tuning based on real-time combustion result,
but rather only bases the injector duration on predefined "maps" in its
ROM. So, the ECU does vary the injector duration and spark timing, but
only based on what it "thinks" is best for a given situation, but would
still not be "closed loop". You really need to somehow measure the
exhaust. Is my understanding correct?
This makes sense, but isn't the O2 sensor just another input for the
ECU? Is it any different from the other sensors, that the ECU uses to
vary timing and injection? What makes O2 so special, if the responses
to it are also based on a ROM "map"?
based on the maps and readings of the sensors, including lambda, the ecu
can then compute in real time the precise amount of fuel to be injected.
if you're interested, there's an open source injector project out there
called [charmingly] "megasquirt". once googled, you can read the whole
nine yards about how injection works, even source code an ecu runs on.
Well,the desired end result is complete combustion(a clean exhaust),and
exhaust O2 content is an indication of how well that's happening.
They are real-time corrections,and measure ACTUAL exhaust output.
(if a plug misfires,or a input-condition sensor is inaccurate,this feedback
corrects for it.it also allows for individual cylinders' injectors to be
corrected,compensating for differing air flow thru the cylinders.They are
not necessarily all equal!)
I believe there may be two 'maps".
One for open-loop,and one for when everything warms to operating temp.
The 2nd map would be much simpler,and smaller in data size,or just a
refinement on (or corrections for) the primary map.
It's like the ECU first sets injector duration for the TPS,IAT,MAP and RPM
via the map,and -then- looks at O2S data and fine-tunes if needed (at op
temp) for optimal exhaust O2 content. It also minimizes the work the
catalytic has to do,-and makes it last longer.
It does take some amount of time to balance the loop once a variable is
changed.(like throttle position or intake air temp)
Loop response cannot be instant,there's always some hysteresis,but it's
inconsequential,until the O2 sensor gets "slow" in it's response(degrades).
OBD-II systems supposedly measure this O2S response time and set a trouble
code (and CEL)if it gets too long(or fails),and also uses a 2nd O2 sensor
to back up the first sensor and monitor the catalytic converter's
performance to ensure low emissions.
Uh, hold on there. Few if any modern fuel injection systems monitor
each cylinder and adjust them independently. At best you have one O2
sensor per bank on a multi-head engine. The ECU has no information
about individual cylinders.
I know that some years ago Saab was working on a system which used an
ionization current passed through the spark plug during the exhaust
cycle to try and do the individual cylinder optimization you talk about,
but I don't know if such a thing ever got into production. Certainly
that is not the scheme in use on the majority of vehicles today.
Closed loop fuel injection also does not correct for ignition problems
like a misfiring spark plug.
Well, I can't claim to know exactly how these systems DO work, but I can
hypothesize that it wouldn't be all that difficult for the ECU to get an idea
what's going on with each cylinder individually. Given timing input, it will
know which cylinder is firing when, and a subsequent change in the O2 sensor
reading is pretty easy to correlate to that cylinder.
As O2 sensor input is split up to separate groups of cylinders, as has already
been discussed here, such calculations become even easier...
Tegger commented not long ago on certain Fords having one
oxygen sensor per cylinder. I googled and found support for
Seems perfectly reasonable to me, timing-wise that the ECU
and O2 sensor could calibrate fuel going to each cylinder.
Closed loop is the way to optimize for low emissions and good fuel
economy. Open loop certainly can work. Most cars manufactured before
1980 were open loop systems be they carbs or early fuel injection.
For those countries where leaded fuel continued to be available the open
loop style carried on for a long time.
I'd guess that the Honda programmers would only edit/alter their ECU
program enough to ignore a missing sensor rather then write another
completely different one for mileage.
Some adventurous soul here could disconnect their O2 sensor and see if the
ECU then flashes the "check engine" light. A brief test.
Fuel could also be an issue. In places where tetra ethyl lead continued
to be used as an additive there would be an O2 sensor contamination
issue. TEL was outlawed in the US many years ago, but much of the rest
of the world continued to use it as an octane improver.
That would explain the lack of O2 sensors in countries where the use of
That could be it! Unleaded fuel was introduced here in 1994, while the
EG line was from 1992-95. Is it true that leaded fuel could damage the
If this is the reason, and not cost-cutting, then could I simply, as
jim says, "retrofit" a sensor? (Taking care to use only unleaded fuel,
The ECU is a P27 (OBD-1 EG JDM Civic 1600 sohc VTEC) which I think is
the same as the one used in the EX US version. However this model has
no VTEC, and no O2 sensor. Could they have left the ECU "as is"?
Wouldn't Honda have used a different ECU code if it's not the same one?
I'm just hoping that it is, since it means I could just plug a new
I'm not after the VTEC, just want to save on gas.
Absolutely. Leaded fuels also deteriorate spark plugs, but they are
readily changed. In the days when leaded fuel was the norm in the US,
typical spark plug change intervals were 12-15k miles. Now with
unleaded fuel and slightly better spark plugs the norm is 100k miles.
TEL leaves nasty deposits when it burns. These rapidly build up on
oxygen sensors and ruin it. They also build up in exhaust systems and
on exhaust valves. Oddly enough, the build-up on exhaust valves acts as
a sort of solid lubricant. When the conversion to unleaded happened in
the US, some older cars had very rapid exhaust valve seat wear due to
the lack of TEL's valve lubricating side effect. Other than for exhaust
valves, everything else about TEL fuel is a downside for the motor!
You would need someone who really knows the Honda fuel injection system
in detail to answer that. Perhaps you can get your hands on a parts
manual for your version and the US version and try to compare what is
different from one to the other. Maybe it is as simple as connecting an
O2 sensor, maybe not. The US version is certainly capable of running
open loop in the case of a failed O2 sensor.
Do you have any friends in Honda's engineering department :) ??????
I believe the ECU would be a different model than a US OBD-I ECU,as a US
ECU will set a code and light the check engine light if the O2 sensor
fails. "not present" counts as "failed".(open)
The Euro ECU's program would have to know to ignore the missing sensor,thus
a different ECU. ECU programming is fixed in PROM,thus a different PROM,and
a different ECU p/n.
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