New 1993 Civic VX owner - O2 question

[93civicvx]

Hello,
Been reading a lot on the forum regarding O2 sensors - which one to buy, costs, wiring types etc etc...

The VX I picked up in Dec of 2010 has/had issues that I am methodically working my way through...
One of them was the dreaded runs like crud/sputters/misses etc.

The bench mark was the 1st tank of gas that yielded 35.5 mpg.
I found that ALL 4 tires were under inflated - 19,19,23 & 29 psi. I inflated them to 45 - 50 psi.
I unplugged the O2 sensor and it runs like a champ now !
With these changes, it yielded 45.6 mpg on the next tank. Based on what I've read, there's gotta be more in there
I know that driving habits are key as well, which I am being VERY conscious of.

My question is, how much does an O2 increase mpg ? Has anyone ever done an comparative analysis of running a tank with the O2 connected vs it disconnected to see the actual mpg increase/decrease ?
Bottom line is I'd like to know how long the pay off would be if I ponied up for one.
As a side question, whats the down fall of NOT having the O2 connected, aside from decreased mpg ?

Thanks for listening and hopefully responding !

Douglas

[tim3058]

The O2 itself may not be the culprit, but by unplugging it the ECM goes into a preprogrammed loop, and no longer considers input from any sensor, regardless of which ones the actual "bad" sensor. There's good info on here about testing the O2, and Haynes manuals have a good section on testing the other sensors.

My car had the same sputtering issues when I got it. Replacing the O2 did nothing for the sputtering. We went through the wiring and ECM pins checking connections and the previous owners ghetto-wiring and must have bumped something into place without knowing it cause its been fine since.
When my CEL comes on, my mpg immediately drops from high 50s to mid-30s mpg hwy (in summer), if thats any help. I'd suggest checking your wiring/connectors.

[93civicvx]

Thanks for the info ! That is certainly not what I would have expected but great info that is "thinking outside the box" for sure !
Be nice if I could find someone who has our car ( 92 -95 VX ) and try their O2 for a mile or two to see what affect it has on the issue... Just to proof the O2 and then proceed with the wiring testing from there which will likely take considerable time...

[tim3058]

Originally Posted by 93civicvx

Thanks for the info ! That is certainly not what I would have expected but great info that is "thinking outside the box" for sure !
Be nice if I could find someone who has our car ( 92 -95 VX ) and try their O2 for a mile or two to see what affect it has on the issue... Just to proof the O2 and then proceed with the wiring testing from there which will likely take considerable time...

Testing the O2 doesn't take too long, if I remember right it basically requires a couple probes into the wires, start it up cold and check voltage, let it warm up, check voltage again. If both values are within a range, the O2 is ok, if not, replace it.

Welcome to the site by the way.

[93civicvx]

Thanks for the follow up and Welcome !
That makes sense and shouldn't be hard to verify.
BTW, I found the Honda service manual ( 92 - 95 Civic ) in PDF on a site called hondahookup. You have to join the site, which is free, then you can download it. I searched for a number of nights before I found it, but was stoked when I did as most places charge a fee for it !
It's already helped out tackling some other issues and I am sure it'll show me what you just stated ( voltages to look for ).
Thanks again !
Douglas

[93civicvx]

Hello,

Is it necessary to reset the ECU when installing a new O2 sensor ?
I took my '93 VX to Honda to inquire about it running crappy and they stated I needed a new O2 - to the tune of $541 !!

They said to disconnect the O2 for the time being, so I did and it runs GREAT !
With the O2 plugged in ( NO CEL ), I get 35 mpg, with it disconnected ( CEL present ), I get 42 - 46 mpg !!

I performed a continuity check of ALL the O2 wires from the plug in the engine bay to the ECU pins - ALL check good...

So, after much research, I bought one for $159 off ebay ( 1992 - 2001 HONDA CIVIC O2 OXYGEN SENSOR FRONT | eBay ).

Upon installation, it behaved the same as the old O2, so... I was wondering, is it necessary to reset the O2 ?

[War_Wagon]

Ummm I'm no expert but I am pretty sure the VX has a wide band O2 sensor, the one you got on ebay appears to just be a normal one. It says it fits your car in the ad, but I always thought the VX had a different one that would read further into the lean scale so it could put the lean burn into effect.

[robertsvx]

Looks like 93civicvx has a california emissions vx.They come with the 4 wire o2 instead of the 5 wire wideband. Also has different ecu. Maybe check the VIN# & ecu SN to confirm previous owner didnt swap something out. I can confirm that if you unplug a 5 wire o2 vx it will definately get worse gas mileage then being plugged in.

[93civicvx]

Sorry I didn't list the VX type I have - it's the Federal version with the 5-wire O2.
I have found a new Honda OEM 5-wire O2 for $361 - far less than the $540 that Honda wants for it at the dealer !!

I did end up resetting the ECU by removing the 7.5 amp fuse ( Memory ) for a number of minutes.
At first, I thought that that was the trick as the car drove for about a mile and a half before crapping out and running rough/sputtering/missing etc. As opposed to the time I I tried the n $159 O2 and only got 2 houses away from my driveway before it sputtered and coughed.

Even with my O2 disconnected, my last tank was 46.5 mpg.
I know with a functioning O2, it's gonna push me into the low 50's mpg !!!!!!
Gotta love it !
Thinking that if the gas prices keep heading up, I'll need to park the car in a locked vault, as it becomes more and more valuable as gas prices rise !! LOL !!

I'm gonna go back and pick the Honda dealers brain about the O2, as they are the ones that said it was bad.

I'll keep you guys posted as to what ends up working for the little O2 finicky VX !

[robertsvx]

I think 46.5mpg is great with o2 unplugged.Thats what i get city/hwy mix mountain roads.I know my mpg is in the 30's with a cel for o2.Something else might be causing it to sputter when it hits lean burn other then o2. Let me know if you figure it out