I decided to replace my primary O2 sensor, first in an attempt to cure my ever-frustrating low-rpm hesitation problem (more on that later), and second in an attempt to reduce fuel/oil consumption, and maybe get an improvement in power & driveability. I never got a CEL indicating it as malfunctioning, but it’s widely speculated that the tolerances for O2 sensor performance by the Honda ECU are quite low. Since the primary (upstream) O2 sensor on our car is solely responsible for changes in the short term & long term fuel trim, as well as the closed-loop situations that we drive in 99% of the time, I figured replacing mine after almost 100,000 miles would be a good idea.
The procedure is really very easy, but I figured if there’s a how-to on changing your oil, this might be of use to someone. On a 1 to 10 scale of difficulty (ranging from an oil change to engine swap), I rate this job a 2, only for the small amount of wire splicing needed. If you splurge for the more expensive application specific sensor w/ the harness all ready, this job is a 1. I estimate an hour & a half of work from start to finish, taking your time.
And of course, all the standard disclaimers apply . . . . information is not guaranteed to be accurate, do this at your own risk, I’m not to be held responsible if you die trying to do this, blah, blah, blah.
Parts needed:
-
Universal 4-wire Walker O2 sensor kit from
www.oxygensensors.com ($59 shipped)
Tools needed:
-jack, jack stands, & blocks; or
ramps & blocks.
-22mm O2 sensor socket(s) – I rented
this set from Autozone for a $15 deposit.
-various
wire splicing & soldering tools
-breaker bar & ratchet
-torque wrench (not required, but recommended)
Original sensor removal:
Once you get the front end in the air (using all standard safety precautions, of course), crawl underneath and you’ll see your
target just in front of the catalytic converter.
Go ahead & detach the
wiring harness for the primary sensor
(the blue one), and unclip the wires from the little hook holding it.
Given the mileage on my car and the fact that it’s been daily-driven through no less than 7 (probably 8) New Hampshire winters, I didn’t fool around & had my trusty
24� breaker bar on hand with the O2 socket set. I’m glad I did, because even with all that leverage, it took some maneuvering to get enough torque on it to break it free. I used the deep socket from the kit on the original sensor. Once it was loosened a couple turns with the breaker bar I swapped to a standard ratchet to crank it the rest of the way
out.
Here’s some
pictures and
side by side comparisons of the old sensor vs. the new. A pretty impressive amount of carbon & crud built up on the original NTK one.
Wiring the new sensor:
The universal kit from
www.oxygensensors.com is really nice. It comes with surprisingly comprehensive directions & all the crimp connectors & shrink tubing you need.
From here you have to figure out what wires match up with eachother. I found the
page with the Honda/Acura harness diagram to not be very useful – it didn’t match the original NTK sensor. But looking at the
first page of the instructions (also linked a couple posts down) I was able to figure out what wires matched up with eachother (basically, a universal type “A� harness matching to a universal type “B� harness). There’s 2 heating wires of the same color, one wire for the ground, and one wire for the signal. A little common sense & some time spent double-checking yourself, and you shouldn’t have any problems figuring it out.
Make sure to get the shrink-tubing on the wires before you start crimping & soldering. And
make your cut so you’ve got an extra 3-5� of length to play with. It would pretty much suck for it to end up being too short.
Here’s a
few pics of the re-wiring process. The instructions recommend a “stagger� splicing, so that all the splices aren’t at the same point in the harness – probably for strength purposes.
No DIY project is complete without a minor screw-up, and this was mine – I forgot to fit the protective wire loom onto the harness before I soldered it up. So with a couple lengthwise cuts and some electrical tape, I managed to
get it on fairly well.
Reinstallation:
This is a no-brainer, just put it back in the way it came out. The O2 kit comes with some high-temp anti-seize stuff, make sure to get that on the threads before it goes in if you want to have some chance of ever getting it out again. I wasn’t able to use the same deep socket on the Walker sensor as I was on the NTK, as the new one was a little bit longer. But the kit had
another socket that worked – not as convenient, but it worked. Torque it down to 35 ft/lbs. If you don’t have a torque wrench, it’s not the end of the world – you should be okay just tightening it a firm but reasonable amount. With a standard 7 or 8 inch ratchet, you’ll need a fair amount of force to get to 35 ft/lbs.
Then just reattach the wiring harness, and clip it up out of the way. Here’s your
final result . . . .
Impressions:
I know subjective impressions on jobs like this are practically worthless, but bottom line, the car feels better. Smoother throttle response, and perhaps some more power. Slightly more concrete evidence of improvement is that the amount of black smoke coming out the tailpipe on hard redlining runs has been greatly reduced (i.e. it's no longer mistaken for a diesel). So hopefully that means it isn’t running as rich as it was before at WOT, which should mean more power & better fuel consumption.
On the tank before the replacement, I got just over 21 mpg, which was all “city� driving in some stupidly hot/humid weather (95+, 75%+ humidity). But my “city� driving is commuting back & forth to work, 4 or 5 stoplights over a 7 mile stretch, ranging from 30-45 mph.
With the new sensor, I just got 28.5 mpg on a 99% highway trip. A/C running full time, and the cruise control set @ 73 for 90% of the trip. The other 10% was pretty hard VTEC’ing, 90+ mph squirts, hard on-ramps, Boston traffic, etc. I’ll let you all know in a week or so how the mileage compares now that I’m back to my standard commute.
I‘ll also see if oil consumption improves, although I doubt it.
As far as the hesitation, it hasn’t happened since I put the new sensor in (about 500 miles). Note that I’m
NOT saying it’s been cured. The jury will be out for at least another month before I allow myself to believe it’s gone . . . . it’s gone AWOL before, only to return with a vengeance. Just a quick run-down, though – 100% stock engine, all regular maintenance is up to date, only does it on part-throttle, low-rpm situations, and it basically feels like I’ve gotten off the throttle for a second or two when I really have not. A passenger would never be able to tell it’s happening, and a mechanic would never be able to recreate it - it’s fairly subtle if you're not familiar with the car. And it happens very unpredictably – maybe 1 out of 10 times. In my efforts to pin it down, I’ve already replaced all the ignition components, fuel filter, TPS sensor, & MAP sensor.
Anyway, hope this helps someone, I’ll update this as there are developments in the mpg & hesitation departments.
