I've read some discussions where people felt over time the O2 sensors can become less accurate without throwing a code.
I know a lot of folks here change knock sensors when they change coolant. Spark plugs get changed as a maintenance item.
O2 sensors are exposed to heat cycles. Just curious what people think. change them, or wait for a code?

 

Change them. They drift over time and they are probably pretty old by now.

 

Alot of people say change them, much like spark plugs but I'll tell you what. I pulled my plugs this spring and they looked so good I just cleaned them, put anti-seize on them and put them back in. As for O2 sensors, if mine are degraded I sure can't tell by how my car runs. Apparently she likes old plugs and sensors. It runs too well to dick around with it. Your results may vary. My car is a 94 auto.

 

The oxygen sensors were originally designed for a 2 year, 50,000 miles service intervals. They should not be left alone until they fail. Testing them is hard without an oscilloscope because the signal is supposed to alternate from Lean to Rich and it is hard to see without the proper equipment. As they get older the signal looses some of the peaks on both ends (top and bottom). It oscillates between back and forth from very low signals to almost .9 volts on the top, the older sensor might give you an .85 in place of the real .9 and it gets worse as it ages. The delay in the signal as it ages has a bad effect on the Engines performance.

I replace my O2 sensors every five years now as the 2 year rule seems kind of dumb on a less frequently driven vehicle. If you have more than 2 you probably have O2's after the catalytic converter to verify the converter is working properly. The sensors before the catalytic converter are the critical ones as they control your fuel mixture.

If you replace your Oxygen sensor you can get better mileage and performance! Older sensors have a bad habit of cooling off while idling for any long stretch and that pops your engine into "Open loop" until you start moving again and then it heats up and goes back into "Closed Loop" and comes back on and is usually noticeable to the driver.

We buy Corvettes for the performance and when you drive around with old worn out O2 sensors you are loosing some of the performance and wasting gasoline.

To me an O2 is just like a air filter or oil filter or any other replaceable part that wears. Why sacrifice gas mileage and performance to save $25 on a O2 sensor? O2 sensors DO wear out, don't wait for it to happen at the wrong time just replace them on your own schedule.

Best regards,
Chris

P.S. The Knock Sensor is not considered a wearable part, to my knowledge. The Oxygen sensor is a wearable part.

 

That is all very odd. I have never heard about changing knock sensors with coolant.

As for your plugs, good to hear she is running right and they looked clean. Did you check the gaps? They can burn open without ever fouling. You can wait until you have a miss to replace them I guess, but PM is supposed to be work done ahead of failure/issues.

O2 Sensors should be replaced regularly. Like a lot of items, the schedule is probably a bit ahead of what actually needs to get done, but being that most of our cars are hobby cars we will probably never see those miles. I doubt I will put 50K miles on my C4 no matter how long I keep it. I usually change mine every 3-4 years if I keep one long enough. Just in case.

 

O2s tend to go bad gradually when they get old, and people notice a drop in MPG, but they don't end up triggering a code until they're really bad.

They are a maintenance item, but a hard age or mileage limit is difficult to put on one. 50K is a fine interval but if everything else is in good order and she's kept tuned, 100+K would probably be fine.

 

IDK about the LT1 motors but the L98 is screwed into the block. If you want to back flush the block, wouldn't you take that and the oil cooler hose out to stick a garden hose in it? It;s cheap enough that you can replace it instead of getting whatever anti-seize they use and put it back. Although it does go through some sort of test at startup so, not sure which way to lean.

I don't buy the long life plug since it don't like to leave it in the block to chance a stuck plug. So if I have to take it out to inspect, might as well get new ones. I do daily drive it as long as there is no snow unless I feel like having something more luxurious than the C4.

As to the O2 sensors, by the time it breaks, it has wasted a lot more in gas mileage so why not change it every so often? Kinda like brake fluid. Flush it every even year so it is easy to remember. I'd say every 5 is an easy way to remember.

 

First I have heard of it TBH. I have always just used a flush product by the instructions, drain the whole system, flush with water, and then re-charge with 50/50 of the "right stuff" for the car. (Green, Red, or Orange). I have never done the full back flush in that manner.

 

How do you drain the system? If you open the petcock, don't you get to drain the radiator and part of the block? I would think some remains in the lower end and "dust" settles if there is anything in it. Supposedly it is a closed system but I don't know if I buy that. People have mentioned of enough build up they have to take the KS out and poke a hole in the crud layer to drain. Can't say it has happened to me but I would like to get as much of the old coolant out as possible. The KS should be torqued to some low value that is specified. Not sure how to reapply the right anti-seize, assuming there is a right one.

 

Part of this may be I have never kept 1 car long enough or put enough miles on one to really have to deal with this. When I had Dexcool in my IROC (PO put it in, big mistake in an old system that is vented) I drained and filled the radiator 4 times before the system was clear. If only taking old out and putting the same in one cycle has been enough...admittedly it is not a full drain and fill but more of a dilute, dump, and recharge procedure. I have never had a cooling system gunk up so bad to force a need to do what you describe.

The worst I had was a 91 5.0 Mustang... heater core was partially plugged. I ran a flush product and followed the instructions, did it twice and refilled with proper coolant and proper mixture. Heat worked again after, dark crap came out both times I drained it, and never had heating or overheating problems with that car for an entire year after - including driving in winter (it was a convertible to boot).

 

Don't know. That is what I have read but I don't keep coolant that long. I dump it every few years. No more than 5. Usually 3. I just felt that draining from the lowest point and back flushing it will stir things up and let it drain out so that is as much as we can get easily.

Never ran a flush product. Although I read MB has a citric acid flush to dissolve crap in the system. I have backflushed a heater core before with the same results as you described. Lo and Behold, we had heat.

 

Not on the vette but the ones in my daily at around 10 years dropped their cycle rate in half according to the tech 2. Supposed to oscillate around 1hz at idle and I wasn't even close to that, they do tend to get lazy and you usually notice by like was said, increased fuel consumption.

 

Yes but few people keep fuel consumption logs so a tenth of a mpg today and another tenth next month loss will go unnoticed. When it drops severely, maybe they might have a light bulb go off and so something. People being what they are will end up shorting themselves in the long run for a small gain today. In the meantime, they make themselves feel better by saying "it runs fine" so no action required.

 

This gets said on these types of boards all the time. The "I used this brand", "I used this style", or "I never touched it" followed by "and it runs fine". Then you ask if they are logging any data and the answer is usually No. So, their computer may be all out of whack compensating, economy may be down 20%, and they are in a location that doesn't do emission testing.... so yea it starts and goes just fine. It doesn't mean it is right.

Heck, I have probably been guilty of that at times.

 

Yea, funny thing is inspection didn't show it either. Fuel trims didn't show it either but I lost something like 2 mpg which is very noticable over a 150 mile commute... the sensors read what was believed to be right so everything looked normal until you saw the graph... which was very noticable. Like a square wave instead of a sine lol.

 

If you log, you know for sure if it is right or not. Problem is what to do when you know what the problem is. As long as you use the butt dyno, you can have something to support your view depending on the way you want to roll. If you want to fix something, the butt dyno says something is wrong. If you don't, the butt dyno also says that. Also, it sounds cool to say you can feel stuff go wrong or if it is right.

 

Just a quick - semi related question.

At WOT doesn't the computer ignore the O2 Sensor Inputs - and go off the tables ? If that is the case, the O2 sensor age shouldn't impact performance.

 

Yes but if you are a race car, WGAS? OTOH, I don't drive WOT as much as I would like to. So it does affect where I am most of the time

 

Yes. But once you come off it it does. You will notice it more in normal driving conditions which is how most people drive....

 

Completely understood !!! My point was just that if the O2 Sensors are "tired" - it won't impact WOT output. I get that "tired" sensors may impact fuel economy, and in some cases - drive-ability - but with respect to "Performance" ... not really !