Advice for stripped threads upstream oxygen sensor exhaust manifold

This is not brain surgery. You torque it to whatever you feel comfortable with. If you strip out the threads, you'll have to repair it with an insert. What's the problem? If you're afraid to work on the car, then don't.

Thanks Clare.

To answer your question of "what did you think was gonna happen?", I pretty much was hoping it would "feel" like I was tapping new threads, as I've tapped things before.

But it just felt loose.

Still, it tightened the last 1/8th of a turn, so, if that's enough of a "bite", then I'm happy.

I don't know how to *test* if the lambda sensor is leaking, but there's no sound coming out of it (of course, the engine is loud so the sound would have to be huge like it was when we moved the car a bit with the sensor out).

Thanks for that choke advice. It must have "some" mechanism of increasing the fuel-to-air to achieve the 14:1 stoichemotry when cold, so that's kind of sort of what I meant by choke.

Basically, it stalls at low speed (which is all we've been able to do) whenever it's transitioning from warm on the gauge (about 10 minutes or so of low-speed driving). It did this *before* the oxygen sensor, so it's unrelated to the sensor.

The OBDII tester gives us a 800 rpm reading at idle. Dunno how to increase the idle speed yet, as this car isn't mine (mine is a bimmer which is a drive by wire mechanism).

Thanks for that advice Clare, where you have always been spot on in accuracy. I'm gonna assume it's tight enough since I did get a good last

1/8th of a turn on it with a wrench, and where I can't think of how else to test it other than to see if the cleared codes come back under 10mph driving (which is all we can do at this time).

If that's the case, then I think the torque is fine.

The funny thing is I wonder why the mechanic who screwed it up didn't just do what I just did. What did he gain by jb welding it (or whatever that gray hard metal-like paste was)?

Right. The error message you got about the sensor was ALSO unrelated to the sensor. The error message says the output of the sensor is out of range. It's out of range because the engine is running way too rich or way too lean.

You don't. You find the vacuum leak or the bad idle control valve or whatever it is that is causing the mixture to be all wrong, and then your idle speed will stabilize and you will be able to accelerate again.

--scott

Understood. The error is just an error in the input, output, or power of the sensor.

Always wanted to buy a good smoke tester at a good price that a home mechanic can make an argument for on cost/benefit analysis.

I think that's what it was, but what only matters now is what comes back!

BTW, I just bought oxygen sensors for three different vehicles, where I

*hate* throwing parts at a problem. I just hate it.

But it turns out to be difficult to *test* oxygen sensors faithfully.

Sure, you can heat them up and look for a voltage, but after trying that, I gave up because a "really bad" oxygen sensor has its own code, but a "slightly bad" oxygen sensor seems to, in my humble experience on two different vehicles, cause one of two different related codes.

That is, in my experience, a. A slightly bad lambda sensor can cause a CAT register to never set b. A alightly bad lambda sensor can cause a "slow response" code

Given that the heat:voltage test of an oxygen sensor isn't really all that accurate for those two things, and given that oxygen sensors are not only relatively cheap but also known to not last more than about 100K miles, I decided on all three vehicles to just "throw the part" at the vehicle.

In the case of the neighbor's CAT register that wouldn't set, it worked.

The neighbor's kid's Mitsubishi is in testing.

I'm still working on the bimmer (having just this week replaced the two front Bosch upstrem lambda sensors).

What's amazing, to me, is that I've never replaced an oxygen sensor before, in my entire life, but I never worked on such old cars either (two decades old each of them).

Having zero prior experience with oxygen sensors, I think sometimes, "throwing parts" at the problem might be OK in the case of emissions codes because: a. Oxygen sensors are not permanent parts anyway, and, b. You have to get past smog (where a ticket is far more expensive), and, c. You can't really test them accurately (from my experiments anyway).

You don't test them on the bench. You use the scanner. You set the scanner to give you a display of the oxygen sensor signal (and it will show the nominal level, but if it's so bad it's setting codes you'll likely see the pointer slammed to one side or another). So now you know what the computer is doing.

You also know what the engine is doing. The exhaust smells rich or lean. You can put your hand over the intake... if it runs better, the engine is too lean.

When you know what the engine is doing and you know what the computer is doing, you know all you need to know about the oxygen sensor. If the computer thinks it's too rich but it's really too lean, it's likely the sensor, but if the computer thinks it's too lean but can't enrichen it out far enough, it's likely not.

Timing and ignition problems will produce poor combustion which will show up as oxygen sensor errors... but you can see THOSE because the computer gives you ignition timing information.

The scanner will tell you all of the inputs and all of the outputs.

Ignore the damn codes. The codes let you know that something is out of range but it doesn't tell you anything else. Look at the plots. If you just spend your time staring at the codes you won't understand what is going on inside the box.

They do fail, but the vast majority of 'oxygen sensor' error codes have absolutely nothing to do with the oxygen sensor itself. They are faithfully recording that the exhaust is way wrong.

--scott

It always amazes me the dependence people place on those codes without really understanding the *system* that is generating the codes and, in most cases, the *limitations* of those systems.

I agree with both you and Scott that *most people* (not me, but most people), when they see a sensor code, they replace the sensor.

It could be a temperature sensor for heaven's sake, and they replace the sensor.

As I told Scott, I'm an EE so I know how to test a sensor, but in the case of oxygen sensors, I've had five years' experience with the toyota and bimmer where a bad sensor will make the FTP not set the related monitors for hundreds of miles. IN the case of the toyota, it took about 400 miles, and it took more than a thousand in the case of the bimmer.

In *both* cases, I took it to the smog referee and passed with flying colors, even with the registers unset (since that's what the BAR smog referee did in years past). They don't do that anymore, so you're stuck now.

I know the FTP inside and out, and spoke to the BAR engineers who know it even better than I do. I went over all the dozen conditions that an engine must be in order for a monitor to be set.

Remember, in both cases, the bar smog referee PASSED the vehicle.

The problem is much more sinister than you seem to have experience with. But I do agree with you that *most people* just throw parts at a problem.

What I find hilarious is what happens AFTER people throw parts at a problem. Let's take the two corner cases, assuming, for example, that a problem can have FIVE (for argument's sake) caususes:

1. If they guess right on the first pass, they claim that they are an utter genius, and after that, for the rest of their lives, anyone who has that same problem, they swear the answer is that first solution.
2. If they guess wrong, and have to replace all five parts, they swear that the first four parts were bad, until they finally get to the right part.

Anyway, the main point here is that we all agree that throwing parts at a problem is a crazy way to "fix things" but you have to admit a lot of car problems are fixed that way.

I find the funniest "throwing parts" at a problem to be "brake warp". I'm sure the intelligent ones here know that street rotors just don't warp. So I will assume you know that. (Nobody ever measures warp - but it's easy to measure warp which you do measure for a head, for example.)

So what do the morons do when they get a brake-related vibration at speed? They throw rotors (& sometimes pads & even bigger calipers) at it.

Guess what? That solves the warp! Instantly!

They *think* they're an utter genius. They *think* they proved they had rotor warp.

Every brake vibration for the rest of their lives, is due to "warp". Hehhehheh ....

Q: Why does this work? A: Because the *short term* solution is *different* than the long-term one!

While brake-related judder can be caused by many things (look up the Tire Rack vibration flow chart as just one example), let's assume that judder was due to uneven pad deposition.

You can't measure that stuff (not with home equipment you can't). So the rotors measure fine (not that anyone who thinks they warp measures anything).

What happened in the case of "warp", is that there was uneven pad deposition (let's say for this case), and so, replacing (or machining) the rotors "solved" the problem but - get this - the warp comes back.

The guy who *thinks* the rotors warped is dumbfounded.

The short term solution solved the "warp", but the long term solution didn't. Q: What's the short term solution? A: Change your rotors (or machine them or rebed them).

Q: What's the long term solution? A: Change your braking habits.

My point is that, while I'm not a mechanic, and while I only have the experience of the cars that I own or that friends/neighbors own, I generally troubleshoot a problem to the UNDERSTANDING of teh cause of the problem.

In the case of oxygen sensors, I know, from my experience with two old vehicles, that an o2 sensor can be just bad enough to not set codes but to take between 400 and 1000 miles to set all the registers - even as the emissions are perfect.

If you can diagnose *that*, you'd be my hero! Likewise, if you can suggest a working $100 smoke machine, I'd love you!

You seem to have skills that I don't have since you can "feel" and "hear" things that I can't.

I do have live data and freeze frame though, but I'm not sure what to look for.

You seem to have sensitive powers of smelling that I don't have.

For example, it has been four or five years running now that the bimmer wouldn't set a register after clearing the codes (two different smog cycles) where, finally, after many hundreds of miles, the registers all finally will set.

And trust me, I know the FTP (federal test procedure) drive cycle, and specifically the BMW drive cycle just as well as you do. I've been on the phone with CARB for an hour, talking with the engineers, asking why a register wouldn't set.

I've been to the smog referee multiple times (always I pass).

No funny smells though. So you must have a very sensitive nose!

The first time I took it to the state smog referee who passed it even with the registers unset - and they literally took almost an hour - two people besides - to smog it. They climbed all over that car, looking for smoke, looking at the engine - looking up stuff in their Mitchells to see if it was modded - looking underneath, etc.

But now you can no longer effectively use the smog referee anymore.

No smells though. So your powers of smell are far greater than mine ever will be.

Remember, the sensor is working as the code is NOT an oxygen sensor code. There is no code on the bimmer. The register just won't set.

Again, you have powers of sense that I just will never have.

Anyway, lean is so easy to know about that it's not funny.

If the bimmer is running lean (and they all do, if you own a bimmer, you'll know why I can confidently say that), then you get a lean condition code.

The bimmer is filled with them.

The way I've learned to diagnose a lean condition is a good smoke machine. At least on a bimmer it is.

The CCV hoses, for example, are deep in the bowels of the engine. The secondary air tubes, for example, are way hidden near the top.

I made my own smoke machine, but it sucks.

Maybe. I think you know far more than I do. The only reliable data I would have is freeze frame and live data. On the Bimmer, I have INPA/EDIABAS on a PC (and DIS, Progman, etc.) so that tells me a lot.

But you have to know exactly what to look for. I don't.

I don't understand.

Timing, nowadays, isn't usually an issue.

You have to realize that I "think" that an "almost good almost bad" sensor is hard to diagnose. It won't set a sensor code. It will just prevent the related register from being set.

You have to understand that I'm an electrical engineer. I'm not your typical person.

You may think I'm the typical person. But I'm not. (Being an EE doesn't make me automatically a car mechanic though.)

The typical person, both you and I agree, sees a code "related to X", so they replace the sensor X.

Me? I test things.

If the sensor related to X has a code for X, then that just tells me something is wrong with: a. the power to sensor x b. the data inputs to sensor x c. the data outputs of sensor x

The problem you have to realize that the bimmer and toyota had, which the mitsubishi did not have, is that there were zero codes. The only problem was the cat-related register wouldn't set.

After speaking to CARB on the phone, who gave me all the reasons that could happen, we agreed, together, that the only thing that made sense was that the sensor was good enough not to set a code but just bad enough not to allow the cat-related readiness monitor to set.

On the Mitsubishi, it was different as it's a "new" used car so, since I didn't know the history of the sensor, I decided to replace it anyway since it could be as old as 175K miles for all I knew.

Yup. A slightly bad sensor can be nursed for five years & pass smog. (Ask me how I know that.)

It seems that you may not have had the experience I have with a sensor that is good enough to pass smog wonderfully, even by the BAR referee, but which is bad enough not to allow a cat-related register to set.

If you can diagnose that, from the live data and freeze frame data, I'd love to know how because that would be an art unto itself.

Well, THERE is your problem. Look at what is going on with a correctly running engine.

It is a closed loop system. Data comes in from the lambda sensor, and once the machine is warmed-up and the system is running closed-loop, the oxygen concentration is used by the computer to set the mixture control.

You can watch it on the scanner... watch the sensor value when you open and close the throttle by hand, watch it when you squirt a little WD-40 in there. The output of the lambda sensor goes into a second order function that is nonlinear but time-invariant and what comes out is the error for the mixture. The mixture is adjusted in realtime based on that error value.

If you do not understand that this is a simple single-loop feeback system, we have a problem.

All that is nice, but who cares? Get the engine running well. When the engine runs well, you won't have to worry about smog testing. The key is to get the engine running well.

The bit gets set when a certain amount of time has taken place without particular parameters being out of range. If the bit isn't being set, something is going out of the nominal range. Looking at the values in the scanner will tell you what the inputs and outputs are, and if you have the BMW scanner you can see a lot of the intermediate calculations going on as well.

Stop wasting your time worrying about the bits not being set and worry about why the engine isn't running as well as it could be.

[irrelevant junk removed about diagnosing vacuum leaks]

That tells you EVERYTHING you need to know about what is going on with the computer. You get to see all the inputs and all the outputs, and you should have a pretty good notion of what the computer algorithm is if you have read the manuals.

NOW you need to learn to know what is going on with the engine, using your basic senses. When what is going on with the engine is at variance with what the computer sees, you have found the problem.

It's clear that you don't. It's a feedback loop. Do you remember control theory in school? The computer sees the input, it uses it to adjust the output. If the input is wrong, the output will be wrong in the opposite direction.

Ignition timing is OFTEN an issue. Valve timing isn't so often an issue, but you get a free valve timing test when you're checking the ignition timing anyway.

The computer controls the ignition timing, and it does so based on a number of inputs most notably the ping sensor. The computer will advance and retard the timing, and you can see it happening on the scanner display. It does not always do so properly.

In fact on some modern engines (like BMWs with VANOS), the computer has control over the valve timing and that might be based on feedback or it might just be a lookup table where RPM goes into the function and VANOS servo position comes out. Again, the scanner will let you watch it happening, the manual will describe how it's supposed to happen, and your brain can correlate the two.

This is because you're fixated on the codes. Stop worrying about the codes, stop worrying about the register bits, start worrying about how well the engine is running.

Then start acting like an engineer and stop acting like a board swapper.

Of COURSE you can diagnose that from the realtime scanner data. That's what the scanner is FOR. Stop worrying about the stupid codes, stop worrying about errors and register bits, start thinking about what it takes for the mixture to be correct and how far off the mixture is likely to be.

If the oxygen sensor output is in the normal range, but the injector duty cycles are all way out of the normal range, you have a mixture problem. Because the computer is working hard to move the sensor values into that normal range.

It won't set any codes, it won't produce any errors, but the car won't run right. Maybe you have a leak, maybe you have a plugged injector, maybe you have low fuel rail pressure. The computer lets you see that there is a problem, THEN you can start measuring things to see where it is.

Because the system is closed-loop, the computer will compensate for problems in the system... until it no longer can and THEN once it get catastrophically bad and something is totally out range, THEN it will set an error.

--scott

I don't take anything at face value - I look things up.

However, I am not a metallurgist, so I first admit I didn't know if a rotor "can" or "cannot" truly warp (as in potato chip) at street speeds - so I looked up a few things about the temperature needed to cause true warpage of a cast-iron rotor...

Raybestos says: "Brake rotors do not warp from heat..."

This says: "Rotors are cast in extreme heat ?X three to five times greater than the most aggressive braking situation. Physically ??warping?? a rotor would require a similar application of extreme heat, which is impossible."

This says: "...the temperature required to make metal that resilient soft enough to simply bend would be tremendous."

This says that there are adverse effects starting at 1200dF: "When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness."

This says: "in more than 40 years of professional racing, including the Shelby/Ford GT 40s ?V one of the most intense brake development program in history - I have never seen a warped brake disc."

These say the myth of warped rotors started in the 1970's:

This non-scientific thread, which we can quickly assume isn't scientific so let's just take it as a reasonable point of view only, says that the surface may get to 600dF but the rest of the rotor is at a lower temperature than the surface.

I know you guys hate me for "book knowledge", but the answer on temperature seems pretty clear so I will argue no further unless actual references are supplied, as I already know tons of people *think* rotors warp, but it seems that anyone who has actually measured it, apparently thinks not (where true warpage would be easy to measure if you have the equipment to measure head warp).

Hi Clare,

You should be warned that I'm intelligent so I can *read* a peer-reviewed scientific paper, unlike, it seems, most people, who can't comprehend what a paper says. I've read a billion of them, so, bear in mind that I can understand what the authors are trying to say, even as they use words differently than we do.

Reading onward, I think the authors make a critical mistake in not defining their terms, particularly when they use the word "warp" in this sentence, which is the first time it appears in the paper... "It is known that disk warping or uneven disk thicknesses induce pulsation during brake applications."

Clearly it is well known that "warp" (as in potato) and "uneven thickness" are two completely different things - which means that this particular set of Asian authors (M. W. ShinG. H. JangJ. K. KimH. Y. KimHo Jang) are likely ignorant of what "warp" means - or - they simply assume that it means something that it doesn't mean (i.e., warp and thickness variation are completely different things - they just are).

They then compound their errors in a sentence not far from that last horrid sentence, saying "When the disk temperature is increased by friction heat during braking, the heat often causes dimensional instability of the disk, permanently modifying the runout or disk thickness variation (DTV) of a disk and producing brake judder."

WTF?

These Asian guys don't seem to comprehend the English language. It's well known that DTV and runout are two completely different things. They just are. Everyone knows that (except them).

I think the reason they didn't care to use correct words is that they didn't really care about any of those things - what they cared about, it seems, was the effect of heat treating on residual stress which resulted in a less pronounced runout measurement.

The end of the introduction concludes with the idiotically worded sentence: "While the disk warping during heat treatment was measured using a static DTV measurement unit..." Which clearly shows they're using the word "warp" differently than we are (simply because it's a fact that warp and DTV are two different things).

It appears that Ripley and Kirstein (Ref 12) paper might be more appropriate since they showed that the relaxation of the residual stress in the disk could lead to disk distortion. (We have to look at that paper to find out how they defined "disk distortion" though.)

I just posted a query to alt.usage.english as to why these particular Asian authors can't seem to comprehend the difference between "warp" and "runout" and "dtv", all of which they clearly equate in their paper - where all of them are different things. Why can't people figure out warp versus runout versus disc thickness variation

Unfortunately, since the Asian authors don't even comprehend what "warp" actually means, that paper is useless for our purposes, IMHO, simply because they never once measured warpage. Not once.

I completely understand how they *used* the term "warp"; but it's not the same thing that I'm talking about.

What they measured was DTV and runout, and what they were caring about was how heat treating affected those due to the interaction of residual stress after subsequent heating.

This article, by apparently American authors, uses the terms the way I do:

Stop the Warped Rotors Myth and Service Brakes the Right Way They advise: "Starting today, remove ?warped rotor? from your vocabulary."

Where they discuss "lateral runout" and "disc thickness variation", which are NOT the same thing as warp (as in potato).

They're just not.

For christ's sake, WGAF?

Hi Clare, Let's stop this nonsense.

That paper clearly and obviously measured two things: a. Lateral runout b. Disc thickness variation

Never once did that paper mention measurement of warp (as in potato chip).

I'm OK if people suggest a paper because I love to learn, but you have to assume I'm intelligent enough to know that just googling for the word warp connected with temperature doesn't mean the paper shows *anything* about warp happening with temperature.

Maybe most people here deal with people who can't comprehend what a paper says, but I can read almost any paper (I read Physics papers all the time) and if I want to, I can comprehend what they say.

That paper said absolutely nothing about warp (as in potato chip).

I'm not chastising you. I *appreciate* that you tried to show that the disc can get to a temperature that is hot enough to cause warp, as I had already provided multiple references which said that such temperatures are impossible in street use.

It's a valid question.

If someone can provide a paper that proves that such temperatures actually commonly happen, I'll *read* (and comprehend) that paper.

But don't throw a paper at me that says absolutely zero about warp. (Please assume I'm intelligent enough to read & comprehend the paper.)

:) I am NOT chastising you. I'm just telling the truth - which is that paper had nothing to do with warp even though the Korean authors used the word in the paper.

They were talking about: a. Lateral runout, and, b. Disc thickness variation (among other things, like heat treating effects.)

WGAF?

Why Give a Fuck?

There are good reasons to give a f*ck, since, a) Clare suggested the paper, so I read it. b) Are you chastising me for reading Clare's reference? c) Or are you chastising me for *understanding* what it said?

Similarly, I don't know how many dollars are wasted every year on people

*thinking* their rotors warped, when they can't possibly warp (according to the references I provided) simply because the temperatures needed are impossible to attain for the entire rotor thickness.

Let's just assume that a billion dollars a year are *wasted* by morons who can't comprehend the difference between disc thickness variation, lateral runout, and true warp.

Worse - if I ever have a judder (and, at times, I do), then it matters a lot that I *know* that warp can't possibly occur - so I know that the long-term solution is not to buy "Tundra upgrades", which people spend hundreds of dollars on that common but worthless imaginary panacea all the freaking time!

This is a group that is supposed to *understand* that which we fix, right?

If this group is supposed to *understand* a problem well enough to fix it, then it matters that brake rotors just don't warp (they can't get hot enough, based on the references I already quoted).

If someone can show a reference that shows that brake rotos can get hot enough in street use to actually warp (as in potato chip), then I'll *read* that reference.

You guys love to hate me for having "book knowledge", but having book knowledge is better than having the wrong solution isn't it?

The reason it matters is that people implement the wrong solution because they can't comprehend that rotors can't get hot enough to warp in street use (according to multiple references - which hasn't been refuted by anyone here).

Note, that Korean reference that Clare provided may have been translated from Korean (we don't know yet), where this seems to be a portion of the funding (apparently):

1.Department of Materials Science and EngineeringKorea University Seoul Republic of Korea 2.R&D Division Hyundai Motor Company and Kia Motors Corporation Hwaseong-si Republic of Korea

FFSGOY