Hi guys

 

I have a Ford Fiesta Titanium 2012 1.4 petrol. The EML is on for the following codes (this was checked late Sept so not sure if there are additional PC’s):

 

- P0171 System Too Lean Bank 1

- P0420 Catalyst System Efficiency Below Threshold (Bank 1)

 

The fuel economy is TERRIBLE. I’m talking an average of 32mpg, running about 27mpg at 60-70mph on the motorway.

 

Furthermore, this used to happen within 10 mins of a cold start but is occurring more often, but when pressing the accelerator/throttle down, the car will not respond for a good couple of seconds and then it will start responding again. If stationary, the RPM will drop to about 500 rpm (as if the car is going to stall) and then revives itself a couple seconds later

 

I have no idea what are causing these issues but I have a strong feeling they’re all related. Possible cracked exhaust manifold or faulty lambda sensor?

 

Could someone please give me some tips or suggestions, because I’m at the end of my tether with this car and it’d be much appreciated

Based on experience I had with a 2001 focus 1600 petrol I wonder if it has an air leak on a rubber pipe around the inlet manifold. I might be wrong but I think your engine is similar design / layout. 

See pic, see yellow part of dipstick slightly up and to left you sill see a split in rubber pipe. Hard to inspect whole pipe in situ.  Pic taken from eBay - didn’t expect to find pic with a split in pipe

My tip is to take it to a garage to be looked at, which could you could have done at time since September.

Clean the t-map sensor and throttle body