Finally passed my California smog

The previous test results labeled my 93 S-10 Blazer as a "Gross Polluter". Hydrocarbons (HC) were almost 4 times greater than the maximum permitted while Carbon Monoxide (CO) was almost 7 times greater than the maximum limit. Black smoke was belching out of the exhaust pipe and mileage was so bad you could see the gas guage moving downward as you drove.

I really should'nt have done the smog test because it was obvious that something was wrong but I thought that adding a little fuel enhancer and some freeway time would blow out the cobwebs in my engine. WRONG!!

Two major repairs (possibly related) solved the problems of RICH mixture and inability to start. Replacing the "spider" and "nut kit" fixed the RICH mixture and replacing the fuel pump solved the starting problem.

The reason for this post is that if others have similar problems, put a little more highway time on the system than I did. I barely passed the 15 MPH HC test with a measurement of 88 (max 90). The smog tech said that there probably was a lot of carbon in the exhaust system to result in a high reading.

I was afraid that my catalytic converter may have gone south because of the carbon but it did not. The tech said that it was because my engine does not have an air pump and some other stuff that the carbon would not effect the Cat. which it didn't.

Another thing I would like to mention is that I did not mess with the oxygen sensor. A lot of folks replace the O2 sensor thinking it will solve their problem. On my 93 model, after replacing the fuel injection system, I could tell that the O2 sensor was doing its job because it was regulating the lean/rich fuel mixture properly in closed-loop mode.

You still replace the O2 sensor.

It has been exposed to years of rich conditions which only will damage it.

I changed mine even though they were still "working" and what a difference.

You still replace the O2 sensor.

It has been exposed to years of rich conditions which only will damage it.

I changed mine even though they were still "working" and what a difference.

My O2 sensor was probably exposed to not more than 2 -3 weeks of rich conditions. If it ain't broke ..........

By the way, what was the difference you noticed? acceleration, mileage, smooth idle, etc.? I've replaced the O2s on several other cars that I've owned and never noticed any difference.

Since my last post, I looked this up on Wikipedia.

Common failure modes (of O2 sensors)
Lambda probes (O2 sensors) have a limited lifespan since the exposed sensor element is subjected to high temperatures which causes fatigue over time. Probes become sluggish, failing to react quickly to changes in the condition of the exhaust gases. This can be caused by contamination from the engine, fuel or additives. One common fault is silicon buildup on the probe sensor. A common source of silicon contamination is through the use of silicone sealant in repairing water system leaks. Another common cause of silicon buildup is engine coolant being burnt in the engine's combustion chamber, as is often the case with a blown head gasket. Lead build-up from the use of lead additives or leaded petrol will also damage the probe, as will carbon build-up from excessive burning of engine oil. Phosphorus in the burnt oil is also a specific damaging contaminant (but the phosphorus is part of a very beneficial additive called ZDDP which as of 2005 is yet to be replaced with a less 'damaging' (to the sensor or emissions equipment) yet equally effective (in protecting the motor life) substitute. It would be expected that a probe would last for 3 years or 40,000 miles (about 64,000 km), but it has been observed that probes will last for up to 3 times this length. [Also, oxygen sensors have been used successfully for 2 years of racing with leaded gas when the sensor is put into a non-leaded gas burning vehicle to 'burn' off the lead then putting it back, etc. (from geneberg.com)]

My Stuff
It seems from this info that the O2 sensor is a fairly robust (pardon the buzz word) device if it not contaminated by certain chemicals in the exhaust stream, rich mixture or unburned hydrocarbons not being mentioned.

Based on this information, it would not be unreasonable to replace the O2 sensor since I'm at 100K in mileage but if the engine is running great and it passed California emissions tests, is it really necessary to do it now?

By the way, my 93 S10 Blazer is not OBD-II and has only one O2 sensor. Would that be a reason to replace it since there is less diagnostic information available?

I'm welcome to any Facts? Opinions? Rules of Thumb? Old Wives Tales? that would help myself and others replace O2 sensors when their time has come and not do it as a knee jerk parts replacement response to a mis-diagnosed problem.

But, how many miles are on the existing one?

But, how many miles are on the existing one?

All of them, 100K. As the article says, maybe I'm good to 120K. Possibly more. My point is that I have not seen or heard of a replacement schedule for O2 sensors so what is the generally accepted practice? And for what reasons? An SES light? Failure to pass an emissions test?

I don't think you can tell by driveability that your O2 sensor is bad but then, what do I know!

A slow O2 sensor can cause all sort of problems from hesitation to idle problems.

100k is a good time to change at least the one in front of the cat out. I think you have only one anyways.

Also, you should reset your base timing by unhooking the beige and brown wire under you glove box area under the carpet and setting the timing to zero if it hasn't been done.

A slow O2 sensor can cause all sort of problems from hesitation to idle problems.

100k is a good time to change at least the one in front of the cat out. I think you have only one anyways.

Also, you should reset your base timing by unhooking the beige and brown wire under you glove box area under the carpet and setting the timing to zero if it hasn't been done.

Engine is running very well. Great idle. The only thing I've noticed is a slight vibration when the Air Conditioning solonoid kicks in. More so than what I remember it to be. But then, there's been a hell of a lot of changes since I last drove the car.

Base timing was set to TDC per specs. as you mentioned. This setting was checked as part of the California emissions test.

Well the O2 sensing a false lean and richening the mixture can cause this too.

Just giving you pointers. :)