I'm in need of probably replacing my Oxygen Sensor.
Yet what functions does the Oxygen Sensor control?
And when "does it operate"?
Open loop, cold operation or closed loop, "normal" driving?
Thanks

 

The computer runs in open loop until all of the 3 happen:

1. Engine running for at least a few minutes
2. Coolant over 77 degrees Fahrenheit
3. Oxy sensor warms up

The computer can tell the oxy sensor's warmed up by the exhaust because it starts to see a "changing" value from the sensor. When the sensor's cold, it stays at a certain voltage (I think it's a half volt?)... as soon as the sensor warms up enough to operate, the voltage starts to change- and the computer knows the oxy sensor's ready.

Once all of the above 3 happen, the computer goes into closed loop and "adds" the oxy sensor to it's list of sensors to check.

 

Timing
Throttle postion sensor
cold injector part of Fuel Injectors
Thanks tho.

 

Hey Tom...if the o2 is bad and is never sends a signal...then what? does the car code for o2, or just run crappy? Mine did not improve as much as it should have at the track this last time. No codes, but I have been thinking with it running so rich, maybe it fouled the o2...One of these days I'm going to buy a blasted computer checker that reads all the values as its running!

 

Yup, if it never sends a signal, you'll get a code. But if it's gunked up and manages to have some kind of signal coming out, you won't get a code at all.

 

Mine was all white and had some brownish tint...nothing too gunky though! No codes for O2 in a long while though! We swapped it anyway to see if it might have had some influence in the poor runningat the track...heck the car was running rich enough to destroy my cat in a year...stands to reason it could have killed a O2 sensor in that time. Do you have to wipe (disconnect batt) the computer after changing the o2? Ked had asked that in another thread and got me wondering!

 

WOW! i really need to get my site up and running. There is so much people just don't know about FI in general. My site will be free knowledge on Engine Basics, Electrical Basics, Emissions/Driveability diag and various other related stuff.

O2 sensors actually create a voltage. We have single wire o2's on our cars. The purple wire out of the O2 is the signal wire and it ground through the exhaust pipe to complete the cicuit back to the computer.

O2 Sensors don't even operate below about 600*F, Cats either for that matter. During open loop, our ECMs send a 0.450v reference signal down the O2 signal line. As soon as the O2 heats up and starts working, the volatage goes up, since it runs a littel rich in open loop. When the ECM sees this voltage, which could rise up to about 0.950v, it stops sending the signal voltage down the line and starts receiving mixture input from the O2.

Now, the thing to remember is that O2 Sensors ONLY sense the amount of Oxygen in the exhaust. When you're on the lean side, the O2 concentration goes up, when your rich, it's low. As far as voltage goes, the O2 senso reads High (as high as 0.950v) when rich, and low (as low as 0.150v) when lean.

The whole idea is to maintain a 14.7:1 A/F Ratio, which comes out to be that 0.450v from the O2 sensor, that is perfect. Now the hard part comes in. Catalysts REQUIRE this AVERAGE 14.7:1 mixture to function. Three-way Cats have to parts, and Oxidation bed, and a Reduction bed (from the actual chemical function they serve).

The Oxidation bed Oxidizes HC and CO into CO2 and H2O, and requires a slightly LEAN mixture to do this best. The Reduction portion Reduces NOx into O2, N2O, and N2, but requires a slightly RICH mixture to do this best. So, how do you get the best of both worlds? Back to the O2 sensor we go.

When the Mixture is Rich, the O2 sends a high voltage to the computer, the computer responds by commanding the injectors lean, and when the O2 senses the lean exhaust, the ECM commands a richer mixture. Now, this switch should happen about 5 times/second and should go from extremes in about 100 milliseconds. Freakin' fast, but that's what's required to get the CAT to work right.

If you have a slow O2 sensor, then you'll spend so much time (in computer terms) at the rich lean extreams before the O2 responds, that the CAT won't be albe to do it's job correctly. Because of the chemicals used in CATS, they are very good at Oxidizing, but less efficient at reducing, so with a lazy O2, it's not uncommon to see low HC and CO, but elevated NOx.

Bad O2 Sensors are the biggest contributing factor to the death of a catalyst. If your O2 dies, your Cat isn't long for this world.

If anyone has any questions, please feel ree to email me or PM me. I have plenty of info for everyone, and I hope to have the web site up soon.

 

Nope, but it's a good idea to clear the computer anyway after you have a prolonged rich or lean condition because it clears the block learn, much faster and more efficient than letting it happen on it's own.

 

My O2 sensor recently failed, I think its been longer than recent just too this long to go kaput. Kept getting codes 44,45 the past week and running very very very rich which was fouling my spark plugs in 30 minutes of running

New 32 dollar O2 sensor and a new set of plugs that run at a higher tempature and the 2.8 runs like a champ again

 

My question still not answered.
The Oxy sensor controls things to get a reading.
No problem
BUT doing that function (to get the reading)
the Oxy sensor sends a signal to "what" to make it do "what" to regain the correct reading.
I still plan on changing mine as soon as my new Cat Convertor arrives.
But I am still having cold drivability bucking problems. Happens with part throttle driving, not feather on pedal driving nor wide open throttle driving. Yes, this is lousy for gas & the car.
Is a bad Oxy Sensor making this problem happen?
Recently, after overheating (I fixed that problem), I had warm engine drivability problems (yes engine bucking at certain throttle postioning).
Once I changed the Coolant Temp Sensor (on manifold), the warmed up bucking problem went away. And back on & off went my electric fan. No I did not change the fan sensor, as that wasn't the problem, it was the signal to turn on the fan sensor that lead to fan activation again.
NO I HAVE NEVER touched the throttle postioning sensor. Nor do I really intend to. It's receving a bad signal and that's my problem.

I still have cold morning bucking problem until the engine is "warmed up".
Which is why I plan on also changing the Manifold Air Temp sensor at the air cleaner.

I am asking about sensors that control timing, throttle postion sensor positioning. Does an Oxy sensor affect those items? Or does Oxy Sensor send a signal to "?" Sensor to properly adjust throttle postion sensing & timing?

Without solving my problem bucking drivability problem, I'm almost ready to dump this ride as I'm so tired of this "bucking" problem!

Be seeing you soon 2_point8_boy!

 

The O2 sensor sends the reading to the computer and interprets the voltage as either rich o lean. Once it has this information, it controls teh pulsewidth of the injectors to either make it leaner when it gets a rich reading, or richer when it gets a lean reading. It's only designed to make fine tuning adjustments during closed loop. It' can't make HUGE adjustments to cause a bucking or surging problem.

From what you're saying, it's only during cold start that this happens. Which means open loop. During open loop, the computer uses information from many sensors to adjust the A/F ratio. MAF, TPS, ECT, and IAT.

When you turn the key on, the Computer takes a reading from the ECT to get a base pulse width for how hot the engine is, the colder the engine, the richer the mixture needed, the laonger the pulse width. Once the engine is running, the ECM only needs the ECT inorder to know whether or not to goes closed loop when the temperature is right, as TomP posted.

Now it uses to the MAF/MAP depending on the system you have on your car, your being a MAF system, that's what it uses since you don't even have a MAP. Anyway, it uses the MAF and TPS to figure out load of the engine, this is where the MAJOR A/F adjustment takes place. The entire time you're driving, it's these 2 sensors jobs to tell the computer how much air is entering the engine and how far you have your foot into it. The MAF sets up the main pulse width setting so that the engine runs right around 14.7:1 within a couple points. The the O2 makes the minor adjustments to get it to average 14.7:1. The TPS is there just to tell the computer if there is a major change in Throttle Position. When here is a minor change the A/F mixture is only slightly richened just for acceleration. When you put your foot to the floor, the ECM goes open loop and sends a full rich signal to the injectors, increasing their pulse width to get an A/F Ratio of about 12:1, based on MAF input (air flow).

For your surging problem, I would look into the MAF and TPS. Here's the thing that a lot of people have problems with. Bad components do not always code. They could still be within the spec to not code, but the sensor could be giving the computer false information, causing a bad problem, but the value is still "within" range, so no code. Sometimes you might even get a code assosiated with a problem, but the code has nothing to do with the problem itself.

Take this for example. My car used to have a slightly high idle, like 1100 or so after I came to a stop at a light. The SES light would come on and I would have a stored code for the VSS sensor. If I bliped the pedal, the idle wold come down and the light would go out. Turns out that the problem itself was caused by a weak throttle return spring that didn't let the blade close all the way. When the computer saw that the TPS was just off idle and that I wasn't actually moving, it thought that since I'm off idle and the clutch is out, I should be moving. So since it wasn't getting a signal from the VSS saying that I was moving, it set a code because it wasn't what it expected. I fixed the spring, and have not had the problem in 50,000 miles.

unfortuantly, our ECMs are stupid, they are smater than a lot of older ones and give us a hell of a lot more information, but you have to know how the computer interprets that info.

Check teh TPS and MAF. I don't remember feeling the surging problem when the car was at my shop, but since you said it's a cold start thing, I wouldn't have seen it. Just curiosity, did you replace the ECT with one out a junkyard?

The only things that controls timing is the distributor pickup and the computer. The TPS does a little, but only when you go WOT, the computer then retards the timing a little bit so you don't get a sudden ping when it goes slightly lean at the split second that the blade snaps open.

 

ECT=?
I'm about ready to replace the air sensor on the air cleaner and see what happens.

I'll "get back to ya" within 24 hours to let ya know what happened.
I feel the MAF is doing alright.
From what I saw in the Helms book, the Coolant temp sensor does control TPS, Timing, MAF & cooling fan operation.
The manifold air inlet temp sensor so says the Helm book also affect the coolant temp sensor.
My bucking during warm went away (yet I can feel the smallest hint of bucking, yet now where the violent type in AM).
I still feel the TPS is doing alright.
To me I am looking for items that send signals to the timing & TPS. Oxy sensor seems to affect fuel.
Does the oxy sensor also retard timing with increase of cold, open loop, more fuel?
THANK YOU

 

ECT = Engine Coolant Temperatur Sensor

The only time this sensor does anything is during cold start, trust me on this. Helms manual is good for general stuff, but it's crap for Diagnosing problems. They give you general information because they know that the home mechanic doesn't know how the system actually works. It doesn't even control the fans, a seperate sensor does that.

There is know way for any sensor to modify any other sensors input to the computer, period.

karl, the only way to be sure is to check them, I wish it was just simple enough to guess, the TPS is an easy check. I'll write you an email later.