O2 Sensors

[N.O.C.]

Hey All,

I have located a 2001 Q45 T that I believe might be my next car. The seller said he had the 02 Sensor's replaced. Do you know if this is a one time deal or something that this car runs through routinely? Thanks for any insight.

Karl

[Q45tech]

O2 sensors are much like spark plugs, fuel injectors, filters and knock sensors................devices which wear out and need replacing.

Most things are designed to function for ~~100,000 miles before degrading to the point where the engine runs better with new units than with old ones. Somethings vary with conditions and last longer depending.

O2 sensors degrade by taking longer and longer and longer to switch states.

[paranoidjack]

O2 sensors are much like spark plugs, fuel injectors, filters and knock sensors................devices which wear out and need replacing.

Most things are designed to function for ~~100,000 miles before degrading to the point where the engine runs better with new units than with old ones. Somethings vary with conditions and last longer depending.

O2 sensors degrade by taking longer and longer and longer to switch states.

tech, can you elaborate on this? What does slower "switching states" mean to the average roadwarrior?

[maxnix]

Less precision in the injector timing.

Remember OBD II cars with V engines and true dual exhaust have four, two before the catalytic converters that do the heavy lifting, and two after that do the fine trim.

Why it is always a good idea to replace in pairs as the swtiching rates will be different if one is worn, so everything is a little less precise bank to bank.

[bullittandy]

tech, can you elaborate on this? What does slower "switching states" mean to the average roadwarrior?

I'm not tech but I'll throw my 2 cents in. The sensors read the amount of oxygen in the exhaust and the ecu adjusts the fuel/air mixture accordingly (and probably 10,000 other things), as they age they cannot read the oxygen content fast enough to compensate in for changes.

I would imagine a good analogy would be a old man (like Q45tech-just kidding) trying to hit a fastball.

[N.O.C.]

Thanks for the info, any idea what the charge is on a Q to have them replaced?

[silver2k2]

I didnt know the rears did the fine trim. I thought they simply compared pre-catalytic converter to post-catalytic converter oxygen levels to make sure that the catalytic converter is doing its job

Less precision in the injector timing.

Remember OBD II cars with V engines and true dual exhaust have four, two before the catalytic converters that do the heavy lifting, and two after that do the fine trim.

Why it is always a good idea to replace in pairs as the swtiching rates will be different if one is worn, so everything is a little less precise bank to bank.

[bullittandy]

About $300 for parts and maybe the same for labor-though I did mine myself to save the $.

[maxnix]

Thanks for the info, any idea what the charge is on a Q to have them replaced?

Get OEM from Joe or NTK from http://www.sparkplugs.com, but call to verify as the website is often wrong.

Special wrench required to replace easily. Plenty of posts in IOM.

[Q45tech]

The rear just check the condition of cats as there is a time lag thru the cats that is monitored by rear O2.

Front O2 commads lean ecu responds, injectors lean at next few revolutions, cats responds, 2nd O2 notes the changes and feedsback to ecu, ecu determines cats are still ok. Whole process starts over agin a second later.

If injector is running 1.8 milisecs with 35 psi [cruise] really only about 1.00 millisecs is flowing fuel so a 1% change in fuel flow [14.7 vs 14.85AF] so injector might decline from 1.800 to 1.790 millisecs.

O2 have the capability to suggest ecu changes by +-20% just as MAF do from preprogrammed brand new numbers.

As engines and O2 age normally one might see +- 5% 95%-105% on adaptive fuel trims and still be normal for its age.

+- 10% 90-110% might be cause for concern as likely an injector is dirting up.

Each 4 cylinder bank is separately trimmable but this is still a gross cover up as 3 may be MADE rich or lean to fix one!.....................think about this: 3 cylinders made 3.3% rich to net the bank result of 1 =10% lean

Easy to chart out each O2 cycle and match it with a cylinder to find culprit with digital oscilloscope synced to #1/#2 firing and time delayed until the exhaust occurs and has time to get to O2 [speed distance]

[maxnix]

Easy to chart out each O2 cycle and match it with a cylinder to find culprit with digital oscilloscope synced to #1/#2 firing and time delayed until the exhaust occurs and has time to get to O2 [speed distance]

Seems intuitive that timing (exhaust gas flow) would vary somewhat with rpm, or is that just plain wrong?

[Q45tech]

Sure, 90 degrees between cylinder events obviously happens faster as the rpm increase........................a neat device is nothing but a high temp pressure sensor [microphone that can handle heat] which records the put put from the exhaust pipe with a time base it's software displays rpm and relative peak to peak of each exhaust pulse..................power per cylinder.

Just record the sound on laptop and play back thru a spectrum analyser [software] with fast fourier transform. Or a simple oscilloscope since 4 puffs per rev and 6,000 revs/min = 24,000/60= 400 Hertz or 40 Hertz at idle.

Free download of SA software{http://www.qsl.net/dl4yhf

[AlabamaDan]

Whirl whirl whirl (That's my head as I read this.)

My Q is a little sluggish. I've changed plugs, fuel filter, cleaned MAF, TB, and EGR. I'm going to run some BG44k next long road trip I have.

I wonder if it's related to my o2 sensors?

[Q45tech]

O2 on early Q really only work when warm not at idle.

Like most trim sensors O2 can only shift the mixture a maximum of +-20%.

Sluggish ones might decrease the highway MPG by 10% usual less as ecu takes the average if one works slow.

2.2 mpg pf highway might increase fuel cost by 10% depending on driving style.

Year ago it almost didn't pay when gas was $1 now at $3 [$250 per year or more] it surely does!