I would assume that if its not tuned to run just the one, then yeah it will throw it off, but I am not really sure.

 

No the rear o2 even unplugged wont have anything to do with engine running or performance

Tom

 

...hmm. Well now I'm at a loss as to where to look to find the root of my problem. Thanks for the reply Tom.

 

The car is probably going into 'Open Loop, fault' mode because of this...in which case, it runs off a 'safe' AFR (very rich)...which is why your mileage sux.

I had Open Loop, fault issues from running a ristrictive MAF housing, and my mileage also sucked.

 

The rear o2 does nothing to cause it to go open loop

I would see what the front o2 is doing among other things , do you have a way to log things ?

Tom

 

I own an Xcal II, but haven't played with the datalogging at all. I suspected the front o2, but I would have thought a CEL for it would have gone on.

Anyway, I pulled the front sensor and cleaned it, following some tutorials that a Google quest gave me. My problem is gone...at least for the most part. It goes back to the old problem (only not *quite* as severe. Before it would almost die, now when it comes back, it's not nearly that bad) at times, but seems to clear up after a little while (1-2 minutes at most).

My assumption is the front oxygen sensor really does need to be replaced, as from what I have read, no level of cleaning can completely dissolve the carbon deposits that build up on the sensor.

The next time I get a chance to grab my Xcal from home, I"ll see what I can get it to tell me.

 

does the second o2 throw cel if its unplugged?

 

Yes and it will cause the car to go rich (open loop). Back in the day it wouldn't because it only monitored the cat, but now the computer will very briefly fluctuate between rich and lean once per drive cycle to check both front and rear and if it gets contradictory results a certain number of drive cycles in a row it will go to open loop.
The important thing to remember is that today's OBD systems are so complex that you can't unplug one sensor and not have it screw at least one other thing up.

 

FOR THE LAST TIME THE SECOND O2 HAS NOTHING TO DO WITH IT GOING INTO OPEN LOOP!!!!

The Second O2 sensors ONLY job is to determine the efficentcy of the CAT NOTHING ELSE.

 

Read Ford's "OBD System Operation Summary for Gasoline Engines" it says it does more:

As the front UEGO [wide range o2 sensor] sensor ages and gets exposed to contaminants, it can develop a rich or lean bias in its transfer
function. The rear bias control (also called FAOSC – Fore/Aft Oxygen Sensor Control) system is designed to
compensate for any of these bias shifts (offsets) using the downstream HO2S sensor. The "FAOS" monitor looks
for any bias shifts at the stoichiometric point of the front UEGO sensor lambda curve. If the UEGO has developed a
bias beyond the point for which it can be compensated for, lean (P2096, P2098) or rich (P2097, P2099) fault codes
will be set.

 

Yes it sets fault codes but is NOT the determing factor for the engine going open loop from the rear o2 being unplugged

Everyones a tuner these days

Tom

 

OK, I'm confused... then please explain this quote from the same manual

Due to the fact that intrusively driving the CMS sensor rich will cause drivability and emission concerns, there are
other several condition counters that have to fail prior to intrusively forcing the sensor to go rich...

If it does nothing except check the cat how can it cause drivability concerns especially when earlier the same manual said most failures of the cat were because the cat was exhausted and not plugged?

I may not be a tuner but I have a 2 year degree in computers and electronics and work on a 2 million dollar machine for a living that is much more complicated than any Focus you or I will ever work on, so you will understand my natural curiosity in everything about my car.

 

The rear o2 can measure heat and add fuel (very rare), once the fault is set the ECU no longer is able to use the rear o2 and no longer looks at it and relies on the front o2 sensor as long as the front o2 is working properly it will keep the engine in the proper fueling

Your quote sais it self "there are
other several condition counters that have to fail prior to intrusively forcing the sensor to go rich... " To go rich not to go open loop and the top quote also sais nothing about going open loop but driving it under a rich condition will cause driveability issues again nothing about it going open loop

The rear o2 has the ability if in place and working to add fuel to cool the CAT as thats is the job of the rear o2 , If it is not there it sets the code and the ECU does nothing as it has no information and does not set the ECU to open loop like the front failing can do


Tom

 

Thank you for clearing that up for me.

 

Well, it looks like, regardless of it going 'Open Loop' or not, the system can go rich from rear O2 failure?? Which makes this argument somewhat pointless...doesn't it?

He's clearly having a rich condition, as evident from his mileage. If the only change he made was disconnect the rear O2 (I think the ECU can probably compensate for the highflow cat difference), then my suspicions tell me it's the rear O2 causing this...

If not the O2 by itself, which Tom says, then the combination of the rear O2 and something else causing the issues...
I'd replace the front O2 regardless at this point, and see what happens.

 

Well, it looks like, regardless of it going 'Open Loop' or not, the system can go rich from rear O2 failure??

No if the rear sensor fails it will not cause the system to go rich, the only changes the rear O2 can make (and they are very small changes) are to help control the temp of the catalyst... trying to keep it in the optimum operating range.

If the sensor fails all you're going to do is get a code letting you know it failed and nothing more.

In the tune there are no tables for the rear O2, only an on and off switch. Weather you are running rich or lean is soley controlled by the front O2 sensor.

 

From the way I understand it, and Tom, clear this up for me if I'm wrong, the rear o2 will set a code if it detects a rich/lean condition, and then pretty much throws the data from that sensor to the wayside after the code is thrown.

However, the portion of the quote from whatever manual that came from that explains the bias compensations seems to be taking place. The car seems to go rich once (or twice) per drive cylce, and then clear up. This makes me think that the system is indeed attempting to remedy something, then realizing it can't fix the problem, and then goes back to whatever it was running off of before, as the misfire/rich condition completely disappears and everything goes back to normal.

The other option is that the front o2 is just wonky, and is causing everything.

 

The rear o2 only changes fuel if the cat temps are high if cat temps are not high then no fuel changes are done , if that was the case then turning off the rear o2 would mean changes in the fueling would need to be addressed

The front o2 , tps , timing and a few other things controles the MPG , Me I would log the front o2 and see what it is reading as well as TPS and load anything more then doing that is all speculation

100`s of Foci owners before him have unhooked/mil elim the rear o2 and never had this issue

Tom

 

I would log the front o2 and see what it is reading as well as TPS and load anything more then doing that is all speculation

I cant count how many times ive told people this...


Good luck with SCT.

 

Well, the next time I get home, I'll grab my Xcal and do some logging.

 

If you will IM me hpdyno on AOL or email me I will help you with what to log and look over the logs for you to give you my opinion

Tom

 

Thanks Tom, that'd be great. I probably won't be able to get to my Xcal for a day or two, but is there anything special I should know ahead of time? Only thing I've used it for so far is to scan/clear codes and flash.

 

Naaa logging is very straight forward

Tom

 

So, this doesn't have much to do with this thread, but I figured I'd post here anyway, in case someone has an answer to my problem.

I was setting my Xcall II up for logging (which required updating the firmware), and something went awry in the process. The LCD on the device said "SCT Bootloader" and something else under it, and then it froze there. Live Update spat out an error at me, and now nothing happens when I plug the Xcall into a USB port OR to the OBD port. No lights, sounds. Nothing.

It appears that Live Update successfully erased the ROM on the device, and then failed to flash the new firmware after, leaving it bricked. That's my thought at least....any ideas? I emailed SCT on Saturday, but I thought I'd see what everyone thought...

 

Call them 407-774-2447

Tom

 

Make sure you do all that kind of stuff indoors or bring it out to car get it done then take it back in. I have noticed my xcal will not work in cold weather. It freezes or only loads partial data. And by cold I mean below 60.

 

I was under my car today changing the dogbone with the VF Engineering one, what a pain this is becoming.

Well got the motor mount today and the Ford book says I should be able to pull the two bolts for the mount and be able to pull the motor mount. Well those two bolt's weren't a problem, also read the following thread of FF.

http://www.focusfanatics.com/forum/...um/general-technical-chat/26094-how-vf-engineering-rear-mount-install-pics.html

So removed the two motor mount bolts completely but the bracket bolts won't move at all, so decided to spray them with some PB Blaster and let it soak. At this point tried using a 13 socket and a cheater bar on my 3/8 drive, end up breaking the Snap on socket and still can't get the bolt's loose.

The motor mount won't come out with just removing the motor mount bolts.

Any suggestions at this point I might have to pull the Cat to get more room to be able to get to the two bolts, can't get a 1/2 drive with socket in there, and bought another 3/8 drive 12 point 13 socket, moves the whole engine and trans but won't break the bolt loose.

Going to let it soak over night and see if that helps.

Also since I was already there decided to look at the rear O2 sensor since it was changed by the owner before me, and If I didn't know better I would say it is bent away from the half shaft, so I'm pretty sure the right half shaft must have hit it and bent it away from the shaft, don't see any marking on the shaft side or on the sensor, and I am assuming it is still working, since it passed smog in February, I live in the Emissions Nazi State...Also isn't there suppose to be a heat shield on the bottom of the cat? I see three bolts going into it from the bottom

Bottom line get a tune from Tom and have him shut it off, put a Wideband AEM gauge in your car and put the sensor in the hole for the 2nd O2 sensor and have Tom tune it with the Wideband and turn off the sensor. I'm sure if you hide the gauge in your glove box, they would never know that the sensor is a wideband, not the narrow band that is stock and only controls the temperature of the cat. Or you could wire the old sensor to think it's there when it's not, a capacitor and a resistor will do the trick, and put out your CEL....

With Tom's tune your car will run better and is probably the best mod you can do to these cars, plus if you do any upgrades or mods you get NA tune updates as you progress with your bolt on parts and you can data log and he would be able to tell you exactly what's going on with your car, In my opinion his offerings are priceless.

 

Will it come out from between the motor side plates by rocking the engine?

If you don't have to pry/hammer too much that may be the trick to avoid loosening the plate. Twist it out of the way once out from between.

 

I've tried getting it out when I pull on the bolt the engine moves forward towards the bumper, it doesn't want to come out from the motor side plates by rocking it either way, it almost clears the support bracket from the smaller side of the mount. WD 40's post shows moving the bracket, and If I could get the bolt out it would be a piece of cake. Then again the top bracket bolt won't budge either.

At this point I decided to get a fresh start at it in the morning, it's dark now and thinking of away to get that thing out. What should have been 20 minutes is turning out to be a lot more. Wish I had my air tools, it would probably come out with my air wrench...

I think it's time for a nice cold one...

 

Pull on the bolt? IDK what one you mean.

I was assuming you got the bolts out that pass through the mount, might need the car side one back in loosely to help pull the mount from between the engine side plates.

 

Easy way to do this, can't get the bolts loose on the bracket underneath, so I thought about it for awhile, and decided to pull the top transmission/engine mount on the drivers side, easy to get to since I have the AEM CAI installed so the 4 bolts are right in your face. And easy to unbolt them. Lift the transmission from underneath with a floor jack and a 2 by 4. And bingo the stupid KOREAN part came right out. No need to unbolt the bolts from the bracket this way, and the new VF Engineered part fits right in place.

Now I am wondering if the other mounts are cheap made KOREAN mounts, guess it could be worse, they could have been Made in CHINA...[race]

 

I got both bolts out of the dogbone mount, the front bolt goes thru the bracket that is the back bolt in the bracket. The other two are forward towards the bumper that won't? move in the bracket. So I can't rotate the bracket to get the small side of the dogbone out.