02 sensor and better gas mileage

[AK]

I had an oxygen sensor replaced.

Prior to that I got 20 mpg in the city for my CX7.

Now I am getting 21.5 mpg.

Could that increase be due to the replacement of the O2 sensor?

Thanks.

[Scott Dorsey]

If your O2 sensor was reading low and causing the computer to run the engine too rich, then yes.

But it all depends on what kind of engine it is and what kind of control system came with it and how the sensor failed.

--scott

[micky]

So if now I get codes P0171 and P0174, which means that both banks are running lean, does that mean replacing the sensors will cause the opposite of what AK had, richer mixturen and decreased mpg?

This is a serious question, even though I'm sure I'm wrong for some reason.

2005 Toyota Solara XLE with V6 3.3L engine

[Scott Dorsey]

Those codes don't mean that at all. Those codes mean the computer THINKS both banks are running lean.

If the computer thinks the engine is running lean, the computer will try to make it richer. It may or may not succeed depending on what is broken.

So all those error codes tell you is that SOMETHING is wrong with the mixture, it doesn't tell you anything at all about what it is.

All the codes are useful for is to tell you something is wrong so you can look at the sensor and actuator plots on the scanner.

--scott

[Steve W.]

Changing the sensors will do nothing but show the same codes again. Those codes you posted mean the sensors are working. They are seeing that there is excess oxygen in the exhaust stream compared to what they expect based on the incoming airflow numbers. The issue is not them but in the engine. As both are full bank lean codes I would look at the fuel trims and the O2 live data and check for vacuum leaks or an intake leak that is letting in unmetered air. As you don't post any P0300 range codes I doubt it's fuel pressure as that will commonly set misfire codes as well as the lean codes.

[micky]

I did buy a code reader last year that would read the live data, but what I should look for has been mostly a mystery since then, until the video below. I found it a few days ago but just had time to watch it.

Cars are much more complicated than when I was a boy, or even a teenager, and I've said for years and told quite a few people that anyone smart enough to be a good mechanic these days could succeed in a lot of fields.

Thanks. I found a long video that went over at least some of the things to do with a P0171.

He ended up finding a leaky brake booster and a somewhat bad MAF sensor, but more importantly he goes into some detail about what everything means.

You and some of the other people here know everything that is in this video. I miss the days when there were people here who knew less than I do. They woudl benefit more from this post than you or the others here will.

[Steve W.]

I don't know everything but I'm pretty good at diagnostic and repair work on vehicles.

How much do you really want to know about modern engine diagnostics?

[Steve W.]

Oh where he is checking the hoses, a quick trick is to use carb cleaner and spray it around the hoses. If the engine rpm suddenly jumps look in the area you were spraying for a leak.

[micky]

I made a lot notes based on what he said.

Just enough to fix my car, and maybe a little more. :-)

I used the scanner today and the short and long term trims tracked the results of the guy who made the video, at idle and up to 2500rpm. Also the MAF value (in metric) and the ECT, Spark, Load, and IAT seemed on track. Mine starts at OL and goes quickly to CL for both banks.

I forgot to look at the 02BnSn, but I think they're stored in the scanner. Yes, I posted them below, if that's what Review refers to.

The scanner is inside with me, but the notes are in the car. I'll post them here later.

He sprayed with water, hoping to hear a hiss, but not with carb clean.

I was going to spray with brake cleaner, because it says No Residue, but maybe carb cleaner is better? (He didn't say why not, not a word about spraying with other things.)

If that doesn't find it (and I did look everywhere I could think of last year, using propane), I'm going to disconnect the purge solenoid and plug that hose, and then disconnect the brake booster and plug that one, the hoses that go into the throttle body. That's how he found a major problem with his brake booster.

He used a vacuum tester to plug each hose in turn that goes to the throttle body, but seems to me I don't need a tester. I can assume there is some vacuum if the engine is running and it doesn't matter how much, and all I need to do is use a pencil or something bigger to plug each hose.

Last time when I was trying to find a vacuum leak, I didn't know and didn't think about the fact that some leaks don't go to the outside, like a leak in a hose does. He didn't name anything other than the cannister circuit** and the brake booster that could have an internal vacuum leak. There are so many hoses, I dont' have much confidence I would think of something else even if it exists. Are there other things I should disconnect? **The cannister circuit of couree includes a long hose almost to the gas tank, which he couldn't feel or spray or look at.

Fixing the brake booster lowered his trim total by 30 points but it was still too high. He found that his MAF sensor was off somewhat and after he replaced that too, everything was good. (Trim total was between +10 and -10.) I replaced my MAF sensor about 10,000 miles ago, on the hope that would fix things. I only used a mimimal code reader th1en so if it made any difference, I don't know, but it didn't get rid of the codes and, I doubt if it's the problem now. AND today, I don't want to guess what my MAF was at idle, but I know it was 9.5 at 2500RPM. His original one started at idle (cold) 0.57 to idle (warm) 1.84, g/sec (and he said

2 to 3 would be better), but even at 2500 rpm, his value would never go over 7 or 8, so I think mine works better. At least I think so.

I'm not sure what I see when I go to Review / Live Data / Location #1 (the only one listed). IIUC, the data there is from this afternooon and it says

DTC_CNT is 2. That makes sense, P0171 and P0174.

02B1S2(v) is 0.680 B2 is 0.680 also O2B1S1 is 3.279 02B2S1 is 3.250 very similar to bank 1 He had said that 3.3 is perfect 14.7 to 1, air to fuel ratio. My two numbers are pretty close but maybe they'd be closer to 3.3 if ...

EQ_RATB2S1 is 0.988 but I don't know what that means and he didn't say, and I havent' taken the time to look it up yet. B1S1 is 1.006, very similar.

SHRTFTB1S2 is N/A. while SHRTFTB2S2 is 99.2 Isn't that strange? In the 4 values 8 lines up, B1S2 and B2S2 are exactly the same. there something wrong with B1S2?

02SLOC is B1S12--B2S12-- whatever that means.

I hope I didn't give too much info.

[micky]

An important thing I left out was that he said "When we raise RPM to

2000, does SHRT get better, or worse, or the same? If it gets better, lower, usually a vacuum leak."

It got lower for him. And for me, it went up a little at first but then went down somewhere between quite a bit and a lot. Numbers, if any, are in the car.

More than one value I saw go in two different directions, and in other aspects of my life, a little bit in one direction at first and much more in the other direction soon after. I think he mentioned that too.

So so far it's looking like a vacuum leak.

Maybe no need to replace either 02 sensor, especially the one behind the engine. OTOH, I've read that they fail with age or miles. 70,000,

100,000 were mentioned and I have 140,000.

[micky]

And he said in the video, "If it's worse or the same, it's probably a fuel delivery or Mass Air flow problem."

[Steve W.]

From what you posted you have a vacuum leak/pirate air issue as the primary problem. You can use brake clean or carb cleaner, they are both more or less paint thinners that burn ok. I use carb cleaner because the older version of brake cleaner is chlorinated and generates toxic gas when burned. The thing to remember though is that in the video he is working on a car different than yours, some things apply, others don't. For instance MAF flow, as engine sizes go up, MAF numbers increase even at idle to feed the larger engine. Try this

Looking at the fuel trims that go up, then start coming down means that it's a medium sized leak. As the throttle opens it goes past the point where the pirate air is the main component and the mixture improves. If it started improving immediately it would be a small leak.

For the sensor data you want to look at it live, and watch what it actually reads, if the front sensors are changing voltages rapidly as the engine runs and the rear sensors stay at a somewhat constant number and don't vary like the fronts, the sensors are working and although they may be worn, they are doing their job and the converters are working. You may be surprised at where a vacuum leak can be, brake booster, PCV system, intake manifold gaskets, a damaged port on the manifold, in the EVAP system and a host of others, some external others internal. OH the wuse of water for leaks is somewhat common, it's because you can use it on a hot or cold engine or one where you have ignition sources like open plug wires or bad coils. The amount of cleaner you will use won't be an issue though, just be sure to start on a cold engine. Usually something like an intake leak will get better as the engine warms up so you want to catch it when it's cold.

[trader_4]

Since he's fiddled around looking for a vacuum leak for awhile already and can't find an obvious one, I'd suggest getting a schematic that shows all the vacuum lines. Then it will be easier to figure out where they tap off from, how to separate that section and plug it. Or try the smoke tester. I've never used one, but have read of other people using them and sounds like in principle it would work.

[Clare Snyder]

Even something STOOPID like the dipstick not sealed.

[micky]

Under the hood is a partial schematic, of thoze hoses related to air pollution. It doesn't include the brake booster, for example, becauae I guess that has no effect on air pollution (except when the diaphragm is broken and they don't count that! Because they only cover what the law makes them cover.)

It also shows 4 vacuum switching valves, and so far I've only found 3 of them. But this morning I disconnected the one connected to EVAP, plugged the tube on the throttle body and it made no change at all in the fuel trim. I also then disconnected the power brake booster, plugged the tube, and it made no change in the fuel trim.

This one is very similar to the schematic for my car:

can click when the cursor ends in + and enlarge the photo.

Can anyone tell me what the rectangle with two hoses ocming out of it is? It's above the MZ in 1MZ-FE at the bottom left of the picture. And above the Vacuum Switching Valve that is above that. This part of my car looks just like this. That is, there is a second VSV, what they label the PWM Vacuum Switching Valve to the right of that white rectangle (and if that were bad, they sell a replacement, from Toyota even.)

But the black-outlined white rectangle is just a silver box with two hoses attached. And two screws holding it to the bracket above the fuel rail. What does it do?

There are two more hoses connected to the throttle body, neither as easy to get off. Neither shown to in the diagram they provide. ONe just goes to the forward valve cover, and iiuc it coudln't be the problem. The other comes from a 90^ bent tube and I can't tell where it goes. Too many things in the way.

I'll try to find more stuff about the 3.3L engine. I have the shop manual for the 3.0L engine from 2000, but those 0.3 liters etc. make a big difference.

I think we talked about this last year, but I was not despairing yet. They have one for sale for 100, another for 120, and one for 900. WRT rental, autozone and advance don't have it, but there was a PepBoys page, so I called the local Pepboys and he knew almost nothing about it. I called maybe a bigger Pepboys and he didnt' either but he asked someone and indded they have such a machine. He didn't even know how much it costs, but the web page said $30. Well worth it if it works. I hope they have someone there who stills knows how to use it. And they want two hours. Maybe more. I guess I can just go and keep busy.

Yes, it does.

[micky]

Oops, I don't want that. I ordered it online and haven't gotten it yet, but it also says the original version is not flammable (unlike the other three versions in green cans, without chlorine),

So how could it work at all if it's not flammable?

There's a chart about a fifth of the way down, comparing 5 different version of Brakleen. Only in the red can is there chlorine but only that one is Not Flammable!

But in videos I watched, they're using Brakleen in that red can! Life is so complicated.

Yes, I see. The engine he's working on is only 4 cylinders. Mine is 6.

I'll print this and do as he says tomorrow.

Yes, I see.

I'll keep looking and look again at places I've looked.

Okay.

[micky]

There certainly are a lot of videos about car repair. I haven't watched it yet but this one is about how to make your own smoke machine! "Easy and fun to build" What could be better than that.

I'm sure it's satisfying to make a good video and have people watch it, but do they also make money somehow?

[micky]

Another guy didnt' buy or build a smoke machhine. He just smoked a cigar, and it worked.

He attached another hose to his brake booster hose, blew into it and found smoke coming out at the EGR valve which had a cracked something or other. Cost him a dollar.

I don't smoke. I wonder if there is a way to do this with only exhaling?

[Steve W.]

A smoke machine is handy but you can do the same testing on a running car with a can of carb cleaner. The idea with the smoke is that it will pressurize everything and the smoke leaks out, It won't show internal leaks though.

I built a paint can style a long time ago, it works. For a cheap smoker you don't need much really, just a can to hold a smoldering fuel source a hose to connect to the vehicle and a small air source to push the smoke. Even a cheap aquarium pump will do that. You want between 1/2 and

1 psi of pressure as higher pressures can damage EVAP parts. A cheap way to get that is a BBQ regulator. Fuel wise I've seen people use the same materials that beekeepers put in their smokers, and even seen people rig those up to work as well.

[Steve W.]

If you like visit 2carpros.com Put in as much info about your issue as you can and one of the crew can look up the line routing and parts on that car and give you much more info including pictures and other tests.