new Oxygen Sensor and Spark Plugs helped

[proudcapitalist]

Hello,
I thought there might be a few of you out there who could benefit from my recent experiences. I have a 1994 GT (5S-FE) with a manual transmission, which has never given me any real problems. I've taken pretty good care of it over the years, but a few weeks ago prior to getting my registration renewed, it failed a smog test. I don't know if the limits here in Vegas are even as strict as they are in California. I had never failed one previously. The printout showed failure in just one area: "High Speed CO". It was 1.61% (the limit is 1.20%). The tech told me he sometimes sees failure levels much higher than that, which was somewhat encouraging.

I asked him what was the likely culprit, and he said based on elevated levels of CO, the first thing he would try is the front oxygen sensor (the one BEFORE the catalytic converter, not the one after). It is very easy to see and access. He asked if it had ever been replaced... I said I bought the car in 1998 with 43,000 miles, and I never replaced any sensors. Looking at it, and immediately around it, there were no scratches and it appeared to be the original part. He said with most makes/models the front oxygen sensor should be replaced anyway after about 75,000 miles (such sensors are exposed to hellish conditions). I phoned a local Toyota dealership and the person I spoke with recommended no more than 90,000 miles. I did not verify the information beyond what those two people said. My car has 121,000. It has always idled and accellerated smoothly, and I don't get poor mileage or anything (around 25 mpg, mostly city driving... although I rarely check my mileage) but based on their recommendations, I decided to replace the oxygen sensor. I made sure I ordered the original equipment sensor (Denso 234-1053). I ordered online from Amazon which was much cheaper compared to several local phone calls I made. It was very easy to install, partially because it already has the proper connector, without having to splice wire like with the cheaper sensors. Then I went on a test drive and the engine seemed to be a bit more responsive... the accelleration was smoother (not much, but noticeable) ... the early part immediately after shifting/letting the clutch out.

Also, after thumbing through my owner's manual (just the small basic one in my glove box) I decided to also replace my spark plugs, as according to the printed recommendation, it was time to do so. Besides, I figured that could also help "clean up" my emissions, along with other benefits. As with the sensor, I wanted to use original equipment, so I bought NGK 2978 spark plugs. Pretty easy to install, using an extension to get the socket down deep enough (plugs are way down in). Well, not surprisingly, the engine ran even better. Since then, it seems to start a bit quicker, idles smooth as butter, accellerates smoother.. just seems to run better. Note: I don't want to make too big of a deal about this, as it ran pretty well before.. but even a little improvement is noticeable, and surely helpful in various ways. I guess as time goes on, some decreases in performance are so gradual that a person usually does not notice, so when replacing a few things that directly affect the combustion, it IS noticeable.

Anyway, the bottom line for me is... I just had the smog re-test done yesterday, and it passed. I was relieved, but not surprised. Because it was done on the same testing machine as the first test two weeks ago, I assume it was the new oxygen sensor and spark plugs that made the difference. So if YOUR car fails a smog test because of emitting too much "CO" (I can't speak for "HC" or "NOx"... I think those are the other two things they test for, but I'm not sure) you might want to replace the sensor and/or the plugs, based on your car's maintenance history, and advice that you get from the smog technician or your mechanic. I figured that the OE (original equipment) parts would be worth the extra money. Even if you might have one or more other problems contributing to the test failure, if nothing else the new sensor and plugs should help the engine run smoother, get at least a little better mileage, and maybe prevent some other type of problem or two.

HTH,
Mark