Fiesta ST 2013 failed emission test

[gaminn]

Hi guys,
yesterday I failed emission test with my Fiesta ST (manufactured March 2013, it has no upgrades apart from air filter I think). I also almost failed the test two years ago, but I assumed this was caused by not properly heated motor. Also my car repair service didn't find anything two years ago.

This is what they measured during emission test yesterday:

idling:
Revs (should be 700-800): 749
CO (max 0.3): 0.795

higher revs:
Revs (should be 2400 - 3000): 2681
CO (max 0.2): 0,757
O2 sensor: (0.97 - 1.03): 0.972

My Fiesta has never lit any warning icon on the dashboard. Also diagnostic device doesn't see any error code. I talked to two repair services and they both told me this is difficult to diagnose, they would simply start blindly changing spark plugs, O2 sensors, etc...

The car has 108 000 km.

What would you recommend to do in my case? Thanks

 

[CarGuy]

O2 sensors.

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[gaminn]

O2 sensors.

Thanks. It would be nice if the problem is just O2 sensors. Would you replace only upstream or also downstream (BTW: are they different parts or are they identical)? Is is possible to confirm that O2 sensor is bad from voltage it outputs? I think OBD diagnostic device can see O2 sensors voltage, right?

 

[TyphoonFiST]

Thanks. It would be nice if the problem is just O2 sensors. Would you replace upstream, downstream or both? Is is possible to confirm that O2 sensor is bad from voltage it outputs? I think OBD diagnostic device can see O2 sensors voltage, right?

How many Kilometers/ miles on the vehicle?

 

[gaminn]

108 000 km (and if it is important - two years ago when I almost failed it was 85 000 km)

 

[TyphoonFiST]

If it was me id do throw In some new plugs both o2's and call it a day and get retested. O2 sensors get dirty over time and become slow to react therefore increasing emissions.

 

[Ford ST]

The upstream O2 sensor is the only one that has any control of your air fuel ratios. The downstream O2 sensor measures the efficiency of the catalytic converter.

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[gaminn]

OK, I'll replace spark plugs (they should be replaced anyway at 120 000 km) and upstream O2 sensor.

 

[Dpro]

When was the last time you changed your oil? I have found changing oil can help with passiing smog tests.

 

[gaminn]

When was the last time you changed your oil? I have found changing oil can help with passiing smog tests.

9 months and 10 000 km ago. This is good idea as I will have to do it anyway in a few months.

 

[dmb]

a nice drive at 130+ kph before the test will help too and its fun. whats your state think they are california? that sucks.

 

[gaminn]

I had that fun ride before the test...nothing :/

I'm from Europe, Czech Republic. Last year the rules to pass emission test tightened in my country (data from the test device and surveillance camera pictures and sound are being transfered online to the supervisory authority) and I guess this is the main reason I passed it two years ago and didn't pass it this week...

 

[maestromaestro]

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