I would certainly start by replacing the leaking gas line. If the system is running rich, it’s too much fuel not too much air.

Checking the O2 sensors is a good idea. You could have a leaky injector or other component in the fuel system that is causing too much fuel to be injected. Have you noticed any change in your fuel economy since those codes showed up?

I have a 2008 C280 Mercedes.

Recently i had the check engine light come on, and it was diagnosed as a faulty thermostat stuck open. They replaced this and all was well, but I still get fault code P0172 and P0175 – Running to rich on bank 1 and bank 2. I reset the EML and every two days the same codes appear.

I have just today changed the air filters, and the sparkplugs to see if that makes a difference, and reset the EML.

Are there any other things this could be? I dont get any smell of fuel and the car runs like a dream, maybe ever so slight rough idle occaiionally when at traffic lights or stationary, but not all the time.

Its driving me nuts as to what it could be, i was thinking nect inline to check / replace would be the O2 sensors and MAF???

Any help would be much appreciated!

Graham.

Perhaps the catalytic converter was removed. OP didn’t specify.

How could it have a “check engine light” but no catalytic converter? This is obviously an Old pre-80’s car.

Yeah, check fuel trims to see if it’s running rich. I would bust out the factory service manual and look at any sensors that are on the high side of normal (particularly the O2 sensors). In other words, look for reading that are not quite abnormal enough to trigger a check engine light but still a little suspicious, if that makes sense. Good luck on your search.

I’m not sure. Sounds like more diagnostics may be needed to determine why it’s running rich, unless a bad ECU is a common problem on these Fiestas and Ford knows that’s the fix for this issue.

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