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Discussion Starter #1
http://www.obd-codes.com/p0141

Is this the upstream or down stream o2 sensor?

Idk why am asking honestly, probably going to replace both anyways.

I do not live in a emissions check state so I could just cut out my cat or would it be best to keep it- read places it does nothing for fuel economy and purpose is to clean exhaust.
 

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Discussion Starter #3
0.o. what man?

After the car- you mean cat?
 

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Discussion Starter #6
Ill be getting a back pressure kit from AZ on or around the 1st. whats the readings I should be seeing?
 

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I was asking about the same thing a few days ago.

The pass & fail PSI is shown on the face of the (AZ version) gauge; one test for idle and another test for 2500 rpm. I am planning to do the same test and will post my results in a related thread I started a few days ago here->
http://www.focusfanatics.com/forum/showthread.php?t=476906

I will try and remember to post my results here also. I am still working on finding, borrowing or buying the gauge. Sadly, AZ does not have this tool in their tool-loan program at my local store.


 

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Discussion Starter #8
AutoZone has one for 60ish.
 

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As others have said, there's only one bank on these engines because they are straight four cylinder configuration. On a V engine you have two cylinder heads, which means two exhaust manifolds, which means two banks.

Toby
 

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Discussion Starter #10
Where is this bank located? Right before the cat?
 

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It just refers to the bank of cylinders, not a specific part or location. If you had a V-8, you would have two sets of oxygen sensors: a set on side 1 (or "bank" 1) and another set on side 2 (or "bank" 2). A straight four-cylinder engine only has one bank of cylinders, 1-4. A V-8 would have a second bank, 5-8.

Toby
 

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Discussion Starter #12
Okay I am lost on how to fix this then. Enlighten me.

And if that is true then why does obd2 output show two 02 sensors and parts websites show an upstream and downstream 02 sensor.
 

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Okay I am lost on how to fix this then. Enlighten me.

And if that is true then why does obd2 output show two 02 sensors and parts websites show an upstream and downstream 02 sensor.
Uhmmm??..... Hey man, I thought your post about getting a backpressure tester was a completely different reason compared to your "Heater Circuit Malfunction" problem.

Doing an exhaust backpressure test is done when suspecting an exhaust restriction. Doing an exhaust backpressure test has nothing to do with the Heater Circuit Malfunction problem.

Heater Circuit Malfunction: you likely have a bad O2 sensor or wiring damage. Start with a good visual inspection of your exhaust manifold & catalytic converter and find the o2 sensors and the wiring for them.

You have two O2 sensors. I have 3 because my car is a PZEV.
 

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A single cylinder bank has two oxygen sensors: one before the catalytic converter (upstream), and one after (downstream). The first one gives feedback to the computer to control performance, the second one simply monitors the efficiency of the catalyst.

Toby
 

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Discussion Starter #15
Uhmmm??..... Hey man, I thought your post about getting a backpressure tester was a completely different reason compared to your "Heater Circuit Malfunction" problem.

Doing an exhaust backpressure test is done when suspecting an exhaust restriction. Doing an exhaust backpressure test has nothing to do with the Heater Circuit Malfunction problem.

Heater Circuit Malfunction: you likely have a bad O2 sensor or wiring damage. Start with a good visual inspection of your exhaust manifold & catalytic converter and find the o2 sensors and the wiring for them.

You have two O2 sensors. I have 3 because my car is a PZEV.
Okay. Bank 1 sensor 2 means I have issue with an 02 sensor, which one or is the code none specific?

As for back pressure test, going to use the gauge assist in testing cat efficiency or am I wrong in thinking that would work?
 

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Okay. Bank 1 sensor 2 means I have issue with an 02 sensor, which one or is the code none specific?

As for back pressure test, going to use the gauge assist in testing cat efficiency or am I wrong in thinking that would work?
Problem lies within the downstream sensor circuit (the one closest to the tail pipe).

Backpressure testing not needed for Cat efficiency testing. Cat efficiency testing is done using other methods; 1-> testing cat temperatures (inlet vs. outlet); 2-> OBD monitoring of O2 sensor voltage. 3-> exhaust gases analysis.

Method 2 (shown above) is a continuous test being done by the PCM while engine is on. Once the PCM detects cat is VERY inefficient (via O2 sensor voltages) PCM will turn on CEL and set DTC P0420. Cat can be bad/inefficient and the PCM not set the DTC. Also, Method 2 (shown above) can be done by you with a handheld OBD scanner.

Wanna know more? Watch this->
https://www.youtube.com/watch?v=9VZ5K8n5jj0

Edit: a Backpressure test would help to I.D. a clogged cat, but does not test efficiency. Cat can be bad/inefficient -OR- clogged -OR- some of both.
 

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Discussion Starter #17
Glad to see your edit cause I was about to say something to that effect. IDC how efficient it is- id cut it out if the back pressure wasn't needed according to my father.
Honestly Id rather just replace the 02's and cat even if they wasn't that bad so that I knew I had good stuff for the next 10 years assuming I had the car that long.

I have a OBDII reader and the down stream voltage is going nuts and jumping all over the place. Least I assume that I remember correctly that the upstream is to change voltage rapido and the downstream was suppose to stay in the 0.005 area, right?

As for CAT temp, I thought about getting a hand held IR? monitor and seeing the temp. I do know the OBDII has cat temp readings but you say in/out needs to be tested.
 

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...and the downstream was suppose to stay in the 0.005 area, right?
0.005 no.
0.5 yes.

Yes, but watch the video again. Interpreting the voltage readings must be carefully done. Some dips below .5Vdc are normal or forgivable. Bad voltages indicate bad cat OR bad O2 sensor, other testing is needed. Yes, do the temperature readings with a IR gun, and with the scan tool if your scan tool reads them.

My cat is failing BOTH of these tests, but my PCM has not set the DTC yet. My PMC is very very tolerant of my cat inefficiency. Thank you PCM, er, Ford. Fortunately, I do not have State emissions testing for another 14 months.

I will be doing a backpressure test as part of (1) confirming a bad cat AND a semi-plugged-up cat/cats and (2) to determine if my exhaust has any excessive backpressure-> this would contribute to an engine performance problem I am having. -Bad MPG, Bog, Hesitation, Bucking sometimes and more so when uphill and under load -AC on. I am guessing I have 2 problems and excessive backpressure might be one of them.
 

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- id cut it out if the back pressure wasn't needed according to my father.
I forgot to comment on that...

Cat is not required for "needed back pressure". You can remove it (some federal laws come into play) and replace it with an aftermarket resonator and muffler setup. If done without a Tune you would be stuck with a CEL and DTC and never pass some/most State emissions testing.

I have two cats. If and when I replace my main cat (the mani-cat) I will likely toss out the secondary cat and replace it with a resonator. Removing the second cat leaves a space/cavity that is perfect for adding-in the resonator. Plus it is cheaper than a new secondary cat.
 

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Discussion Starter #20
So what does Provide pressure?
Arkansas doesn't have emissions testing.
DTC? Nvm I googled.
Will removing the muffler "Lunchbox" cause any issues?
Off to google.

As for cat issues on mine- my car does buck.
 
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