My 95 Civic ESi (Philippine domestic version) is similar to the U.S. EX
version, I think. It has a PH16 engine (PGM-FI, 16Valve, 1.6Li, SOHC
non-vtec, ECU code P27) but has no oxygen sensor. This is common
knowledge here, and there is a plug where the sensor should be. My
question is, is this a great disadvantage in terms of mileage? Average
mileage for civics here is 18 to 24 MPG (~8-10km/liter).
Is the ECU always running in open loop mode? Can we somehow buy an O2
sensor and put it in, and if so, will this buy us much MPG-wise?
Thanks so much in advance.
really? can you post a pic? it's hard to imagine the point of running
fuel injection absent the sensor because without it, the ecu doesn't
know for sure how much gas to inject.
presumably, but you may need to do extensive wiring mods. it could save
you significantly in gas.
double check on this "common knowledge" thing - i've never seen any
electronic fuel injection system that doesn't have a sensor - without
it, the ecu is "blind". check both sides of the cat as well as in the
manifold. it would be amazing if one wasn't there somewhere.
Interesting. Early fuel injection systems sold in the US were indeed
open loop designs, such as the Bosch D-Jetronic which was installed on
many late 1960s and early 1970s era Volkswagens and Volvos. Closed loop
came into general use about the same time as three way catalytic
converters did. Late 1970s and onward.
I suppose that it is possible that car makers built open loop versions
for countries without emissions regulations much later than the 1980s,
but I have no idea how it was done or if it is possible to easily
convert such systems to closed loop operations.
Hello again and thanks for the replies. I've posted photos at this
link, if you're interested:
I think this version (ESi, Philippines) is a "stripped-down" version,
if you will, of the EG 4-door coupe (92-95) with a D16Z6 engine, minus
the VTEC. I've been using the service manual for some time now, and all
other parts match. The manual doesn't say anything about other O2
This may have been done to make it more affordable, even though at the
time this was the top-of-the-line model here. Also, the emission laws
here aren't as strict as in the U.S., and back in the early '90's they
were even less so.
Am I missing something here?? Are our civics "crippled"?
John Horner wrote:
it certainly looks that way! john raises the good point about
pre-catalyst injection systems not having sensors [i'd forgotten that -
it's /so/ long since i've seen one!] and you've posted the pics. but it
still amazes me. the cost of a sensor, in bulk, to a manufacturer has
got to be less than $50. it's astonishing that honda would elect not to
use one - maybe there was a legal reason.
getting back to your original question, you can almost certainly
retrofit, but there will obviously be wiring involved and it would
probably require acquisition of a new ecu. interesting project though!
and you may as well go for the vtec while you're at it!
it's a huge bump in the exhaust, round about where the passenger seat
is. but if you don't have an oxygen sensor, you won't have a cat.
regarding retrofit, it's not essential to have the cat. - the important
bit is the sensor.
Again, depends on your local laws. In BC, if the car came from the manufacturer
with a cat, then it must always have a cat. In most of the province, nobody
will usually notice or care, but legally it must still be there; in the
Vancouver area, where we also have emissions testing, the car won't pass if it
originally had a cat that's now missing, regardless of the year.
Actually the emissions laws here *don't* require it. Even today I
haven't seen any cars that have Cats. But regarding retrofit, TeGGer
over at rec.autos.makers.honda says:
"On road-going cars, the primary purpose of O2 sensors and their
associated hardware/software is emissions, not mileage. Any mileage
increase you see (if any), would be a bonus, and would be a
Some race cars use oxygen sensors to improve mileage during a race, but
these are using ECUs programmed for mileage. Stock ECUs are programmed
. . .
You should count yourself lucky to live in a jurisdiction with more
reasonable emissions laws and thus a simpler vehicle. Honda OEM oxygen
sensors and cats are priced in the hundreds of dollars."
I respect TeGGer's responses, but do you guys think he's right on this
one? What if our cars here in the Philippines are programmed for
mileage, instead of emissions as TeGGer says?
Oh, no slight meant there, Matt. I was just making it clear that I'm
not contemplating anything illegal :)
Anyway, I'm somewhat confused by TeGGer's response over at
rec.autos.makers.honda, where he says that the O2 sensor is simply
there for emissions. He's a resident guru there and I'm inclined to
believe him, but OTOH when someone asks about poor mileage, group
posters usually point to the O2 sensor as the culprit. Also, most
references on the net say that the sensor is vital for normal running.
Anyone have any idea on how this ECU was tweaked to run without an
oxygen sensor? How does running in open loop affect things?
Open loop makes the fuel-air mix richer than optimal(for emissions) ALL the
time,just as it does until the engine warms up to operating temperature.You
have to avoid a too-lean condition in -all- operating conditions,to avoid
damaging the engine.
Closed loop optimizes the fuel-air mix for the leanest possible mix -
without- risking a too-lean condition that could burn a piston or make the
motor run too hot.It minimizes the extra hydrocarbons (rich exhaust)that
the cat-converter has to burn up,for best emissions.
You have a open-loop at the start because the catalytic has not warmed up
yet,nor has the motor.(coolant,plugs)
I doubt it would be worth the expense.
Considering you would have to change the ECU in addition. That's big bucks.
If you're looking for better gas mileage,changing your driving habits would
be far more productive,keeping your tires inflated properly.
It's supposed to;it's a failure of the O2 sensor(missing = "open"
sensor),and the control loop is no longer closed,emissions not controlled.
Your car should have a *different ECU* if it does not have an O2 sensor.
Honda kept the same wiring harness for cost and simplicity,but the ECU
would have to have different programming to ignore the missing O2 sensor
and not flash the CEL.
Since Honda solders in their PROMs,ECUs are different.
Thanks, jim. You make a good point.
I'm really curious about this "open" vs "closed" loop mode. Are we
greatly disadvantaged by always running in open loop? Or are we "lucky"
as TeGGer says? Can't an ECU run in closed loop using just MAP, TPS,
TA, etc sensors?
no, it needs to know "lambda", the actual ratio of fuel to air the
engine is experiencing. the only way to do that is with a sensor.
older sensors only detected what's called "stoichiometry", i.e. when the
mix is perfect. newer sensors are "broad band" and detect the range
typically sought, i.e. lambda from 0.8 to 1.2. [the former is lean, the
latter rich - and peak torque.] either way, a sensor allows the ecu to
tune the engine perfectly for its running conditions. closed loop is
the way to go.
if you want to retrofit, you could look at this as a science experiment
and buy a used ecu online from the states. they're typically in the $30
to $100 range for the standard models.
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