P0420 and Timing Belt

[zLegacies]

Hey guys, so two separate questions:

Background: I have a 2015 Ford Focus 1.0 Ecoboost with 140k on it. I bought it used and ever since being bought, the long term fuel trim is at 14%, short term hovers around 0. After doing my own diagnosis, I replaced both O2 sensors and the purge valve. That didn’t fix the rich condition and I couldn’t find anything else so I brought it to the dealership in which they told me it was normal, and I ended up, chalking it up to the direct injection engine and carbon buildup.
 

Question: P0420 code popped up last week with no other codes. Since I have recently replaced the O2 sensors, is it definitely the cat most likely? Is it worth running a bottle of Cataclean through it or just replacing the cat? Anything to worry about with the cataclean on these engines? Or is there anything else I should be considering?

Also I am trying to determine if it is all worth it since I will also be needing a timing belt as preventative maintenance and I’m sure those are really expensive on this type of engine. I have done them on other cars but there isn’t much instructions on how to do it on this car.

[unofix]

10 minutes ago, zLegacies said:

I will also be needing a timing belt as preventative maintenance and I’m sure those are really expensive on this type of engine. I have done them on other cars but there isn’t much instructions on how to do it on this car.

Replacing the timing belt on a 1.0 Ecoboost engine is not something the home mechanic should even think about.

It takes a Ford main dealer with all the specialist tools, and a fully equipped workshop about 10 hours.

Replacement is due at 100,000 Miles / 160,000 Km or 10 years which ever comes first.

[zLegacies]

Any idea what something like that costs?

[TomsFocus]

The cat probably is knackered by now if it's been run rich for a while.  Cleaning it won't help.  

Not sure of your location but is there any sort of emissions testing regularly carried out for the equivalent of a UK MOT?  Carbon monoxide (CO) figures would show whether the cat is worn out or not.

[zLegacies]

I’m in Massachusetts, I believe they test for emissions at the yearly inspection. Wondering if it’s even worth replacing the cat if it’s the engine that is worn and causing the rich condition. Weird thing is no codes are thrown for the rich condition

[zLegacies]

Also I’m sure it will be back but the check engine light disappeared on my way home from work yesterday 

[rd457]

50 minutes ago, zLegacies said:

I’m in Massachusetts, I believe they test for emissions at the yearly inspection. Wondering if it’s even worth replacing the cat if it’s the engine that is worn and causing the rich condition. Weird thing is no codes are thrown for the rich condition

I'm no expert on the subject, but I think you may be misunderstanding the cause of the rich condition. As I understand it it's perfectly normal to have a bit of carbon build up within the combustion chambers and this has nothing to do with a running rich/lean condition, thus it would be wrong to think of your engine as "worn out". A rich/lean condition simply results from an issue with delivering the intended ratio of fuel-air mixture into the combustion chambers, or a problem taking measurements.

Thus it could result from faulty O2 sensors (bad measurement), but you've already tried replacing those. It could alternatively be due to a faulty fuel pressure regulator (pressure reaching the injectors is greater than it should be causing more fuel than expected to enter the engine), or similarly a faulty injector; From a faulty MAF/MAP/TMAP sensor (measuring air flow); Perhaps an air flow issue from an old clogged up air filter? Or malfunctioning throttle body?; Or a faulty IAT or coolant temperature sensor (affecting calculations?).

Fixing the running rich condition I expect should thus be entirely possible and of reasonably low cost.

Replacing the damaged cat however I'd expect to be rather expensive as I understand it's not typically a cheap component (hence the thievery).

[zLegacies]

That was very helpful. I find it interesting that I have no others codes though and I would think if a sensor is acting up it would throw a code, or even throw a code for a rich condition. I checked today on my ride in and it was saying 17% positive LTFT. I can do the cat myself, but don’t want to if it’s just going to get damaged again from the rich running engine, which I am unsure how to fix since I have already done my own tests, as well as brought it to the dealership who found nothing either

[rd457]

Sure, ah hang on, the list of possible problems I gave earlier was based upon thinking that combustion was running richer than intended, but you're saying it's a positive LTFT value, so that means combustion is being detected as running too lean, forcing the engine to add extra fuel. So in that case the suspects would include a clog in one or more fuel injectors; faulty fuel injector; not enough pressure from the fuel pump; bad oxygen sensor; an air/vacuum leak of some kind; a MAF sensor issue; or misfires due to spark plug issues.

I wouldn't put too much stock in lack of codes being proof that nothing is wrong, I'd look at the actual live data to make my own determination. Something I just read indicates that although LT/ST trims should typically each be within +/-10%, the trigger for a code might not be until one reaches +/-25%, which would explain why you're seeing a trim clearly above the value it should be but yet no code. Also it's commonly pointed out in this forum that not all code scanners are capable of reading all codes, so your scanner could possibly be missing some.

One suggestion that I'm reading is that you should try watching the LTFT under different conditions - while the engine is idling, at 1500rpm and at 2500 rpm, and also "under load" (whilst driving). If it's a high value at idle but not when revs are higher then this suggests causes like a vacuum leak. Alternatively if it remains high consistently then it's more likely to be a fuel supply issue, MAF sensor or temp sensor.