Hey guys.

A few days ago I was at a Ford dealership with my Fiesta (1.0 Ecoboost, 2015, around 80k miles, new timing belt) because the engine light came on repeatedly with the error code p0420 - catalyst efficiency below the threshold.

They told me that they found a crack in the head of piston number 1 and that the engine was burning oil because of this which in turn resulted in a dead catalyst. They suggested a replacement of the engine to me (approx. 6000£) which is sadly economically pointless to do since I bought the car just two months ago for around the same money.

So before the selling the car again I went to another shop to get a second opinion and they surprisingly told me that they think that the engine is fine. It has no loss of oil or coolant, no blue/white smoke out of the exhaust and also the compression in all three cylinders were fine. 

Since I now had two different opinions on the state of the engine I went ahead and bought myself a cheap endoscope to take a look at the piston, the images I took are attached below. I mean, I'm no mechanic by any means and that black line somehow really looks like a big crack in the piston, but couldn't that also just be carbon build up? I'm thinking this because the area that is enclosed by that black line is reflecting the light in the same way as that smaller spot in the left of the picture. Also, If that thing is a crack, how the hell is the car still drivable without the piston coming apart at the first combustion?

I'm thinking about driving to another Ford dealership so they can also take a look at the engine but diagnostics alone cost me already around 500£, so I wanted to first post here and ask about your opinions on the images. 

Another thing I noticed is that the old spark plugs, which I replaced when I did the endoscopy, look pretty black. Could this have something to do with a faulty catalyst in the car? Maybe it delivers some weird sensor readings to the ECU which in turn affects the combustion process, but I don't know....

7 hours ago, approx12 said:

with the error code p0420 - catalyst efficiency below the threshold.

Those photos look fine to me. There a few quite easy and cheap ways you can check to see if there is a crack.

1. Firstly do a compression test on each cylinder. They should all be almost the same. Low cost compression test kits can be bought from the likes of Amazon.
2. Also you can do a 'Hydro Carbon' test on the coolant system to check for exhaust gas in the coolant. Again these can be bought on Amazon for about £24

I would suspect that you have a faulty catalytic converter. Or even just a faulty sensor.

Thank you! I guess I will try the hydro carbon test since the second repair shop already did a compression test and told me it was fine. 

The mechanic there also told me that the exhaust system was pretty rusty and that there is a leak somewhere. They suggested that this was the reason for the bad error code. Does that seem plausible? 

33 minutes ago, approx12 said:

the exhaust system was pretty rusty and that there is a leak somewhere. They suggested that this was the reason for the bad error code. Does that seem plausible? 

That is plausible, an Exhaust leak near or at the Cat can cause that Fault Code. 

If the Exhaust is in good condition apart from the leak then a competent Mechanic could weld it up but if it is in poor condition then replacement might be the best course of action. 

I don't think it's a crack although I note it is positioned at the thinnest section of the piston crown . Much more likely to be carbon build up.

Instead of throwing lots of money at mechanics and tests why not try one of the carbon removal products on the market e.g. Cataclean (worked for me). May give your injectors, piston rings/crowns etc. and Cat Converter a treat.

https://www.gsfcarparts.com/za044780?auto_apply_coupon=ROAD10&gad_source=1&gclid=CjwKCAjw4f6zBhBVEiwATEHFVlV77RWKR4KAo_oy9IShHS_sEpBcR42E6NCf7mtqpuX4bs4MvDY6rRoCXqAQAvD_BwE

 

On 6/29/2024 at 7:25 PM, RayC333 said:

I don't think it's a crack although I note it is positioned at the thinnest section of the piston crown . Much more likely to be carbon build up.

Instead of throwing lots of money at mechanics and tests why not try one of the carbon removal products on the market e.g. Cataclean (worked for me). May give your injectors, piston rings/crowns etc. and Cat Converter a treat.

https://www.gsfcarparts.com/za044780?auto_apply_coupon=ROAD10&gad_source=1&gclid=CjwKCAjw4f6zBhBVEiwATEHFVlV77RWKR4KAo_oy9IShHS_sEpBcR42E6NCf7mtqpuX4bs4MvDY6rRoCXqAQAvD_BwE

 

Has the fault code been back since you used the Cataclean? 
 

Did you reset the code after using it or did the EML go off by itself?

4 hours ago, Focus1.0 said:

Did you reset the code after using it

The original poster has not been back for quite awhile.

Hopefully Ray will be able to help answer your question. 👍