O2 sensor gurus!

[sublauxation]

Just wondering if I've got this backwards.

Not sure if this makes sense but my O2 sensor is stuck high (reading a rich condition) which will induce an actual lean condition.

My code is 2195. I've seen 2 descriptions for it.
1)....O2 sensor Lack of sensor switch indicates lean
2)....O2 sensor switch indicates lean condition

The difference is huge as they are oppposites. Anybody have insight into this?
1) The second description is how it shows up on scanners. Are we supposed to take the codes at face value, or is the first description the logical interpretation of a sensor showing that it's always trying to make the mixture more rich?

 

[gm280]

sub, not sure what type OBDII reader you are using, but the new ones seem to isolate to better readouts. There are so many things that can flag a sensor bad type reading and that is bad. Because you could change every O2 sensor on your vehicle and not solve the mystery. Some times it is something else that causes such a reading. I would actually check the connections for broken or frayed wire insulation. So before changing parts (costly) try and get another OBDII reading from another place to see if a different one will read a better fault more isolated readout. And does it specify if that O2 sensor is pre-catalytic convertor or after the catalytic convertor? You could even take it out on the interstate and drive it for a few highway miles to see if the system cleans itself out first. JMHO!

 

[bruceb58]

On my OBDII software, I can graph the O2 sensors. If you really want to see what's going on, that is the best way. I can graph all 4 O2 sensors. You can easily see which O2 sensor is not working.



Not the cheapest in the world:
https://www.autoenginuity.com/

Just the scan tool is $250.

 

[sublauxation]

They graphed at least the front two sensors (bank 1 and 2), both are showing continuous high voltage rich condition. He's supposed to get back to me to give more info, I want to know what the back sensor is saying, and wondering if that is causing the "lean condition" code to be read. That would make sense. But they keep saying the front sensors are throwing the code and technically if that were true I would think it would be the opposite code for a rich condition. That is, depending on the interpretation of the wording of the code.

On a quick inspection they visually look good from the outside, better than I expected.

If I trusted that it was the O2 sensors I'd replace them myself and save almost enough to buy that scanner. It kills me not to be able to see all the data. When I brought it in the deal was I'd pay only for diagnostics and likely do the fix myself. They had no problem with that. Problem is I don't trust the diagnostics.

A shot of throttle body cleaner into some vapor management hose made it idle perfect which does lean towards it truly being a lean condition.

I'd love to take it on the highway but it doesn't run well enough as I barely got it to the shop a couple blocks away.

 

[sublauxation]

And there are O2 sensor specific codes, none of which are coming up.

 

[bruceb58]

When you looked at a graph of the sensors before and after the Cat, it will look like this. Do you remember what the graph looked like? The graph should be a pulsed waveform like the following. The front and rear O2 sensor should follow each other.

Does your engine consume any oil or do you use something like seafoam that contains oil(very bad for O2 sensor)?

Do you have the corresponding p2196 code for bank2? If you have a lean condition that is caused by an intake leak, you would likely get the code set for bank 2 as well.

 

[sublauxation]

Fronts supposedly both read at the top and don't change. He's trying to tell my the back two after the cat are acting completely normal and show no evidence of a lean condition. That seems odd as if it's truly a result of the fronts showing rich and the PCM then decreasing fuel delivery, shouldn't the back ones show it lean if they're working?

 

[bruceb58]

Correct. That is why I wanted to know what the graphs looked like.

They won't pop a code unless they are out of the specification window. Problem is, the window is wide enough that it may pass.

 

[Fleetwin]

You've got two threads running. Stick with one. Confusing to all involved.

http://forums.iboats.com/forum/other/non-boating-technical-topics/10040501-ford-expy-wont-idle

 

[sublauxation]

Nobody's been involved in the other thread for a while, that's why I started the second more specific to O2 sensors, though yeah, it is a bit confusing, sorry about that.

I'm getting a bit upset as the mechanic is evidently the type who wants to do and not explain. Sadly what he explains makes little sense. Frustration is setting in!

All he says:
Front 2 show high voltage, running rich
Back 2 are normal (though if not throwing a code they should graph lean shouldn't they)
Fuel pressure on the line is normal. (wont tell mo or doesn't know at the injectors.

 

[bruceb58]

Nobody's been involved in the other thread for a while, that's why I started the second more specific to O2 sensors, though yeah, it is a bit confusing, sorry about that.

I'm getting a bit upset as the mechanic is evidently the type who wants to do and not explain. Sadly what he explains makes little sense. Frustration is setting in!

All he says:
Front 2 show high voltage, running rich
Back 2 are normal (though if not throwing a code they should graph lean shouldn't they)
Fuel pressure on the line is normal. (wont tell mo or doesn't know at the injectors.

If the voltage isn't cycling, you may have a bad sensor. Is it?

Have you read this article?

 

[sublauxation]

Thanks Bruce for the info, pretty sure I'll be buying the scanner!

 

[sublauxation]

Sorry about the 2 threads, I didn't want to lose some people who had an anti Ford bias as that thread dried up!

Thanks to everybody who chimed in, it all helped the outcome.

I want to make this come full circle though. I read a lot of forum threads where people had the same problem but dropped off as they figured out what the problem was, only they never posted what that fix was. I want this one to be more useful for any poor soul who comes across it though I'm not sure it will help.

Before bringing it to the shop I did my own smoke test and found small vacuum leaks at the EGR and a small one at the PCV valve hose. I also had a vacuum leak at the brake booster that I knew about. I fixed all 3 and it did run better but still wouldn't idle at all.

I paid the shop for diagnostics and graphing values from their computer. I got the codes on my own, the shop did confirm them.

The codes were 2195 and 2197 (lean condition bank 1 and bank 2, pre cat sensors).

The graph supposedly showed both O2 sensors reading rich with no fluctuation. That makes sense as it would cause a lean condition, but to my thinking it didn't line up with what the codes said. And to have 2 independent O2 sensors go bad on the same morning? Supposedly it also showed the MAF sensor reading properly and good fuel line pressure.

The mechanic gave me an estimate to replace both O2 sensors as he assured me it was the problem. I disagreed with his findings and he no longer likes me. He did listen though, and he has the advantage of being able to simply replace parts until some combo works, then return those that didn't help.

In the end the problem was the MAF sensor. They're not cheap! I was going to go to NAPA and look at a new one for comparison before I even started taking things apart but they didn't have one in stock. Had I been able to do that I would have immediately noticed that the resistor was obviously missing from mine and it would have saved me $120 in mostly bogus diagnositics.

Most importantly, she again purs like a kitten!

Lesson learned: buy the scan tool Bruce posted and just keep doing it all myself!

 

[bruceb58]

I replaced the MAF in my Lexus when I had a bad idle problem when cold. It did affect the acceleration and never set a code. Idle was better when warm which also means it was running lean.

What made you try the MAF?

Sometimes, you just have to shotgun though. On my 99 Silverado, I was having slight stumbling when cold but only at high altitudes. Eventually it started stumbling at sea level which made things easier. I cleaned the MAF which didn't help...actually bought one but didn't install it. Measure the fuel pressure which looked good but was slightly funky. Pulled a vacuum tube off a pressure regulator which had fuel in it . Replaced the $25 fuel pressure regulator and I was fine.

 

[MTboatguy]

Post #4 on the other thread I said " the Mass air flow sensor needs to be tested"

 

[sublauxation]

Post #4 on the other thread I said " the Mass air flow sensor needs to be tested"

I know I confused things with having 2 threads, but the MAF was tested and graphed on the computer. It was said to be working just fine, I don't know if he re tested or interpreted the info wrongly the first time, but the problem was constant, not intermittent so it's not like they somehow missed it running wrong.

Bruce, I didn't try the MAF, the mechanic did. I talked with his boss and explained my doubts on the O2 sensor diagnosis and he agreed that it would be unlikely for both front O2 sensors to go bad the same morning, though not impossible, so he had a pow wow with the mechanic and they approached if from the aspect of what would effect both sides at once. The mechanic told me they changed the MAF despite it looking good on the computer (not sure I believe that, I'm thinking they interpreted it wrong but who knows?) and the truck instantly idled perfectly.

I initially thought the truck had 3 O2 sensors, 2 pre and 1 post cat. Turns out it has 2 cats so 4 sensors in all. That really made me doubt the O2 sensor diagnosis.

 

[bruceb58]

the MAF was tested and graphed on the computer. It was said to be working just fine, I don't know if he re tested or interpreted the info wrongly the first time, but the problem was constant, not intermittent so it's not like they somehow missed it running wrong.

Yes, I saw you post that as well. That was why I was wondering what made you change it.

You don't happen to use a K&N filter do you?

 

[sublauxation]

The filter was clean but not a K&N. I wish I knew the truth, either he read the computer info wrong or this is one of those fluke conditions where the shotgun worked best. His exact words were that the MAF read low when it was chugging and higher when it would actually idle smoothly. That makes sense to me as the way it should be, but I don't know for sure.

The whole thing was definitely weird though so like I said, not sure of the truth. They were going to do the diagnostics only but ended up swapping out the MAF. He charged me $100 in labor which would have been ridiculous except they were originally going to charge me $100 for the diagnostics (actually cheaper than the going rate around here). Their price for just the MAF sensor was $250 but he told me to buy one from Napa and they'd return it in place of the one he put in. I paid $145 at Napa.

 

[MTboatguy]

I have yet to see a scope correctly diagnosis a MAF sensor problem correctly, I have three different scope/meters and none of them can correctly find a MAF problem, and that includes my Snapon.

 

[sublauxation]

I have yet to see a scope correctly diagnosis a MAF sensor problem correctly, I have three different scope/meters and none of them can correctly find a MAF problem, and that includes my Snapon.

You'd almost think that would be one of the easiest parts to diagnose, especially being first in line! I considered just replacing it before bringing it in but since it wouldn't have been returnable it would have been an expensive crapshoot.

Any scanners you recommend? I looked at the one Bruce posted, looks nice.