Might replace bank#1 (firewall) upstream o2 sensor. If no success, look to the bank#1 cat.

 

Downstream would be the one to replace as that tells the PCM the efficiency of the cat. Usually a P0420 & P0430 are accurate, but I have seen O2 sensors fix this problem.

 

I was goin to go to advance auto n use thiers. Do u know if the scanners they offee to use can check the 02? I may just buy a scan tool that works thru smart phones. What do u mean by watch the ltft?

 

I've gotten a free scan from both Advance and Autozone. They usually just let you walk out with the scanner or take your wallet or phone as collateral while you scan the car.

 

Yep.. I work at advance.. we take a driver's license.


Anyways... many of the scanners (usually an Actron brand one) will give you an indication of the O2 sensors.

 

LTFT= Long Time Fuel Trim

 

Ya im there every few weeks scanning this car...lol. not sure how to check the 02 but i assume car will need to be running. Im sure i just look at tool and it will walk me thru process. Any ideas why my evap is never set? I been keeping eye on this car checking codes. Ive drivin almost 1500 miles the one time n evap still not set.

 

Ya im there every few weeks scanning this car...lol. not sure how to check the 02 but i assume car will need to be running. Im sure i just look at tool and I'm will walk me thru process. Any ideas why my evap is never set? I been keeping eye on this car checking codes. Ive drivin almost 1500 miles the one time n evap still not set.

For the evap system to set it needs to be under a very specific amount of variable. My boss used to be a smog tech in cali and there were cars he could never get the evap to pass, but I'm sure that evap not being set won't fail you.

 

New York allows 1 monitor not ready. You've got 800 miles to set the others and pass inspection. Of course, you should fix the problem as time permits.

 

^+1 with las59. If an o2 sensor replacement is going to extinguish the p0420 vs. the bank#1 cat, it'll be the upstream pre-cat bank#1 (firewall) o2 sensor, not the downstream post-cat bank#1 o2 sensor.

 

Post cat O2 tells the computer the efficiency. Pre cat tells the computer what is going on inside the combustion chamber. How would something before the cat tell the computer about anything to deal with its efficiency?

 

Also if your pre cat O2 is lazy and your engine is running rich it may be destroying your cats anyways. Yes replacing the pre cat O2 MAY fix a P0420, but that is not the sensor that tells efficiency. How could you tell the efficiency of something before anything even enters it? Not trying to argue or start anything.

 

It depends on the programming of each car...and how much weight the engineers gave to each sensor's waveform compared to its correct waveform VS the difference between the pre and post cat waveforms. On many Fords replacing a lazy precat 02 sensor can turn off the p0420, but on a lot of other cars it won't. Toyota for example uses the precat A/F sensor to make judgements about the post-cat 02 sensor's efficency. There are no hard an fast rules in driveability diagnostics, so it's pointless to argue about it.

 

So i just double checkn with u guys n gals before i make my move. The pre cat 02 sensor is what i wanna change? This is sensor that runs the air fuel mixture? Do to the fact im gettn such bad gas milage i wanna change sensor that determines fuel mixture. When i order i will be ordering a up stream 02? And i will be changing the 02 before the cat near the firewall. Also shud i stick with green motorcraft o2 . Think i read someplace thats the best plug n play. Thanks for all the advise, this forum has been extremely helpful since i purchased this taurus in november.

 

Yes, NGK, Denso, Bosch, all are fine. Remember, you may have a bank#1 cat issue.

 

Yes i realize that, the sensors are over due to be changed so im gonna give it a shot. So if it works great if not ill get the new cat and the other upstream sensors then ill be 100% good. I just need to have this car to get better mileage. I commute 70 miles a day and im driving my vette everyday because it gets 28 on highway n taurus is getting like 15 it seems. I feeling bad putting so many miles on my corvette , thats what i bought taurus for.

 

So i changed the sensor seems like my problem is solved, Im gettn about 25 mpg. And another thing is that the whole time i had car i always had the smell as if there was a oil leak n was hitting exhaust. Well that was just how rich car must of been running because that smell is gone. Thanks for the help everyone

 

Well glad it worked. But if it was running so rich that your cats couldn't keep up with the amount of fuel being put in them, I woukd say your cats may be at the end of their lifespan or you did some serious damage. IMO

 

ill keep my fingers crossed........

 

But that is just one persons opinion.

 

Take it out for a good, long drive, and get your cats hot for an extended time to cook them as clean as possible. You may be OK with them for a long while still. I have owned 5 Taurii. They can forgive a lot of abuse IMHO.