93 Honda Civic Mileage gone bad

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Elle found a place to get OEM on-line at a nice price for early models. I thought I saved the link but maybe she'll see our plight and repost it.
Mike
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the O2 sensor is

miles. I doubt many

all expect to

on or not). If

we suspect it, I

done with it.

party sensor

early models. I

and repost it.
https://www.automedicsupply.com /
I bought one for my 91 Civic from these folks about a year-and-a-half ago. Good service. No problems. I think their prices are competitive for more recent models, too.
From my reading on the net last year, people say to only buy OEM. Aftermarket are not as reliable.
For the original poster: Check that timing! I monkeyed with mine a bit a month ago, and I think it's why my mileage dropped a bit below 40 mpg on the last three tanks. So darn hard to see the timing marks lined up, especially with middle aged eyes. Or I didn't let the car warm up enough.
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wrote

Thanks much for the URL. I looked,and they did not list the 94 Integra GSR motor,just the RS,LS,SE models. I suspect the O2 sensor would be the same,though. Also,quite a big price difference between the OEM sensors and the universal.I guess you would have to "adapt" the wiring on the uni sensor.(no connector match)
--
Jim Yanik
jyanik
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In my experience, universals come with crimp splices to re-use the connector of the OEM.
Mike
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| > the best thing to do is put in a new one and be done with it. Then why not buy new car & sell off old car ? I heard [i] japs export all their cars >5yr old, in whole or as components, to less developed countries with lower labour cost [ii] in Japan, new cars are cheap & repair costs high. Doesn't USA have the same situation ?
| will a 3rd party sensor suffice? only if it has the same capacitance value ( usually in H i.e. micro Henry ) as the OEM part, so your ECU will not detect any difference
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UH,microhenry is an INDUCTANCE measurement,capacitance is in microfarads,or picofarads.
the O2 sensor might be rated in millivolt output (per oxygen unit).
--
Jim Yanik
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Right about the units, and the output is rather a moot point. The capacitance is immaterial, since it is used as a DC device. All use the same chemistry and are as very nearly identical, with the exception of the heater characteristics. Even at that the heaters are all 12V DC.
The essential characteristics (as I understand them): *open circuit when cold, they are biased to 0.45 VDC to signal an inoperative condition *once they reach something like 450 degrees, they become conductive. If the exhaust has enough CO compared to the outside air, the device becomes a fuel cell and the output rises to approx 0.9 VDC. If the exhaust is lean, the output drops near zero (about 0.1 V is the figure usually given).
If the mixture is close to correct initially, the ECU drives the mixture back and forth across the transition point as rapidly as the feedback allows - thus the need for rapid response. Seven transitions per second is considered good, but I don't have a good handle on how slow is really considered bad. Maybe four... three?
Mike
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Low mileage => more gas or more work by engine for a given baseline hmm ...
I presume you have ruled out obvious driving changes such as altitude/distance/less hwy/more city/lead footing/avg speed etc...
is that automatic tranny ?
- have you noticed an increase in RPM per given cruising speed ? that is at 60 mph you used to be at say 2500 rpm now you are at 3000 rpm ?
- any chance your transmission is the problem maybe you lost 4th/5th gear ??
- if manual are you forgetting to shift into 5th ;)
- since a vtec any chance your engine stuck in vtec high rpm performance mode ? or something wrong with vtec system ?
- has the CHECK engine light come on or blinked recently ? considering VTEC function is controled electronically (ECM function) could be VTEC malfunction > you could try running self diagnostic and look for system error codes ? > maybe try reseting the ECM

i have '93 Civic Si same engine and have never really seen (> 31mpg)
maybe the VTEC was broken before and now it works ?

I usually get about 28-30 , maybe your foot is heavier now :)

using different grade oil (factory recommended) or any new additives ?

ah ha ! thought i had an idea

HTH
most of this was out of Factory Service Manual, a very good book if you like to work on the honda i do not know how chilton/hayes etc compare but the Honda Service manual seems very good
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Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder by oil pressure. RPMs go up = more pressure. at a certain point, the pins slide in and the intake valves use a different cam lobe. I checked when I adjusted the valves, they weren't stuck. But I doubt one VTEC being stuck on one cylinder would change the mileage this much.
Driving habits have not changed.
Nope, Oil is 10w30, hasn't changed.
I have the Factory Service Manual, it's pretty useful.
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Danny Beardsley wrote:

the vtec /is/ applied by oil pressure, but the oil is "switched" on and off from the oil channel by an electrical solenoid. that is in turn controlled by the ecu. simple oil pressure control is subject to too many variables to be reliable.

non-activating vtec is /most/ unlikely to be the cause of declining gas mileage.
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that is what i am talking about, i wish i had read this before posting my rebutal

non-activating may give better gas mileage ?
i was thinking constant-activation, either VTEC solenoid stuck in high rpm mode, which i supppose effectively becomes manual oil pressure control (is that a trick to get lower mid-range performance out of VTECs ?)
or the ECM signals causing VTEC engaging are maybe engaging high rpm mode a bit lower than factory design specs. say engage VTEC at 2500-3000 rpm instead of 4500
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Rob B wrote:

ecu's/ecm's do not get it wrong. they either work, or they don't. and these honda ecu's/ecm's are spectacularly reliable.
of there /is/ a vtec problem, it's more likely solenoid or wiring.
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Thanks guys for the VTEC info... I'd always wondered how oil pressure was stable enough to engage something at a specific RPM. I guess I better read the factory manual a bit closer. I'll find some way to check the solenoid.
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maybe i misunderstand ...
you completely by passed the *EC* (electronic control) part of VTEC variable valve timing and valve lift electronic control system
The mechanics of the VTEC engaging is hydraulic (oil pressure) via the VTEC oil solenoid which performs as you describe *BUT* the control of the VTEC engaging through VTEC solenoid is the ECM which is electronic and uses several measures to control VTEC solenoid operation {rpm, load, temp, speed }

and engine would probably vibrate, seem unbalanced i was thinking about VTEC solenoid or ECM control signal which would affect all the cylinders

well my VTEC electronic info comes from page 5-9 "switchover from one VTEC profile to other is controlled electronically"
so i am just suggesting that one cause for using more gas (your %25 drop in fuel economy) could be fault in the VTEC control, for instance if the VTEC solenoid is stuck in high rpm mode all the time then you would be using more gas, of course i suspect there would be some other symptoms like low rpm and low end rough starting and rough idling, but once you get into 2500 rpms or so it would just seem like great performance
I like the HO2S idea too but there should be some performance problems there as well like rough idling or stumbling or some noticeable performance problem associated with richened air mixture
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Thanks for the VTEC info... I'd always wondered how oil pressure alone was stable enough to engage something at a specific RPM. I guess I better read the factory manual a bit closer. I'll find some way to check the solenoid.
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Danny Beardsley wrote:

Doesn't matter how you drive it. You should still be getting better mpg's.
I second elle's opinion about the oxy sensor(s). The engine computer no longer gets realistic data from the oxy sensor and is running in default mode.
dan
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dan wrote:

id third that. its pre OBD2, so it isnt going to throw a code. if you have 2 sensors, id replace the one *before* the catalytic converter.
on my 98, it went and threw a code. it also ran like crap/stalled at idle.
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Sounds resonable, but then the Check engine light would be lit if the sensor were failing... Well, "should" be it.
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Danny Beardsley wrote:

i dont think itll light up the check engine lamp on a pre-96/OBD2 car. might not even throw a code. but the O2 sensor definately has an effect on the mileage, and by 200k miles with the original sensor, its time to replace.
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Danny Beardsley wrote:

id do a compression test and replace the O2 sensor if its the original one. its due, and directly effects emissions. if its bad, the engine could be running rich. is the tailpipe sooty? were the plugs black? grey? tan?
a small factor could be tire pressure. another factor could be brakes dragging. jack up each wheel and see if they spin freely.
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