Ox sensor cycle time

[panelman]

It's maybe a bit of a simple question for here but....what should the duty cycle of an Ox sensor be?

Mine cycles between 0.2 and 0.8 with a peak to peak time of about 8 sec

I had it in mind that the cycle time should be about 1 sec rather than 8

Comments welcome

 

[franzh]

The actual cycle time can be very fast (sensor reaction time). I have seen it detect an individual lean cylinder, using an lab-scope, not a handheld scanner or DVOM. I think what you are seeing is the reaction to the fuel management system, at idle. The sensor can only react to the fuel mixture it sees after combustion. If you speed the engine to 2000 rpm, I would suspect your cycles would shorten.
Franz

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[Chumley]

Assuming you mean how often per second the ECU - O2 sensor feedback loop should tweak the mixture lean/rich/lean . . . that causes the O2 sensors voltage swing . . .


Older type single wire unheated O2 sensors should cycle at least once per second with the engine at idle provided the O2 sensor is warm and the system is in closed loop. At least 3 times per second at higher RPM's provided everything in the feedback loop is working properly.

The newer type 3 and 4 wire heated O2 sensors in OBD I and OBD II closed feedback loops should react more quickly than the single wire sensors throughout their operating range.

As the O2 sensors age, or become contaminated, their reaction time generally slows down causing the emission levels to rise.

A good fresh O2 sensor all by itself can detect changes in exhaust O2 content and respond with a voltage swing within a few hundreths of a second but the entire feedback loop usually doesn't need to be that responsive. It's based on the load/unload time of the catalytic converter(s)

Chumley

 

[panelman]

Thanks for that....car is a V6 Audi, too old to have OBD. It has one (three wire) sensor for each bank which is fitted before the cat(s).

Seems like the consensus is it's way way too slow so time to change them. What sort of lifespan is normal? These are "only" 11 years/120,000 miles old

 

[NickE]

That sounds about right for the life. (at least in my experience.) My VW jetta needed a new one (I think single wire) after ~80k mi (OBD I 1995).

 

[Chumley]

Panelman: Yep, if your O2 sensors are the originals, chances are they're tired, especially if you have noticed a recent decline in fuel mileage and the engine uses more than about 1 qt. oil per 1500 miles. According to Bosch, they are 100,000 mile maintenance items. Don't wait too long, on V6 Audis, old O2 sensors are well known to cause the catalytic converters (over $400 each) early demise.

Chumley

 

[panelman]

Thanks for that everybody

and finally.....are all sensors the same?

ie can I just buy a pair of cheap generic bosch sensors and splice the cables or do I need to bend over at the Audi dealer?

 

[Chumley]

Panelman: Well, that depends on who you ask. All O2 sensors are not the same quality. Wrong question though.

A better question is, "Considering my 11 year old Audi V6, what is the best value for my dollar that will function properly and "chances are" won't cause any further issues? If that is your question, (which I suspect it is) then, yes, you can use the Bosch 13913 Bosch generic O2 sensors, splice them in, and save several hundred dollars over the OEM Bosch O2 sensors purchased at the Audi dealer or other aftermarket sources. If you live in an area highly subject to corrosive environments, are subject to regular biannual emission checks, do a lousy job of crimping/sealing the splices and as a result fail your emission tests and/or cause your converters to head south, well, you've been warned. Me, I use the generic Bosch sensors all the time.

The Bosch OEM O2 sensors are pricey but pretty much dummy proof. The Bosch universal sensors, less so, but with good practice, usually work fine.

Chumley

 

[panelman]

Chumley

Thanks for re-phrasing my question and your other posts

Dollars is wrong, I have to pay for things in pounds (or body parts at the dealer) and we have an annual emissions test. On the other hand I make my living joining cables together so that they stay joined together so splicing the 13913 to the audi loom should be no problem.

Thanks again for your help