BXW engine Rich fuel mixture

[Skylow]

Hi!
I have a leon 1P from 2008 with the horrible BXW engine, the 1.4mpi with 86hp.
Since i bought it, allways had an O2 sensor bank 1 "system too rich" error.
I've swapped the pre-cat O2 sensor with an used one with the same ref, still get the same error.
One mechanic said it was an O2 sensor fault, other says its the ECU.
Both O2 sensors are working fine, at least both of them give good readings, besides the pre-cat sometimes gets higher than 0.9v and then comes down again.
Spark plugs already changed. Air filter too. I believe the BXW has no maf sensor or anything like that.
In the summer, if i leave the car outside on the sun, it takes 3 or 4 times to start but then runs fine. on cold weather it allways starts and runs fine.
Any tips?
Thanks

 

[R3k1355]

If it doesn't have MAF it surely has MAP, so maybe that sensor is playing up or there's damage to the area and it's getting false readings.

Temp sensor and/or thermostat could also be an issue

 

[mty12345]

Hi!
I have a leon 1P from 2008 with the horrible BXW engine, the 1.4mpi with 86hp.
Since i bought it, allways had an O2 sensor bank 1 "system too rich" error.
I've swapped the pre-cat O2 sensor with an used one with the same ref, still get the same error.
One mechanic said it was an O2 sensor fault, other says its the ECU.
Both O2 sensors are working fine, at least both of them give good readings, besides the pre-cat sometimes gets higher than 0.9v and then comes down again.
Spark plugs already changed. Air filter too. I believe the BXW has no maf sensor or anything like that.
In the summer, if i leave the car outside on the sun, it takes 3 or 4 times to start but then runs fine. on cold weather it allways starts and runs fine.
Any tips?
Thanks

To me, everything points towards the EVAP system being your problem. The EVAP system vents excess fuel tank vapours into the engine at certain times. IF the valve that controls it fails, the engine will be constantly sucking fuel vapour through from the fuel tank, making both the mixture too rich and the car hard to start ,especially in the summer when hot temps cause more tank vapour to evaporate while the car is parked. The valves are cheap enough and easy to change. https://www.autodoc.co.uk/car-parts/breather-valve-fuel-tank-15015/seat/leon/leon-1p1/26552-1-4-16v

I'm never one to suggest throwing parts at a car, but with those classic symptoms i'd be 99% sure i'm right. If you want to be totally sure, you can test the valve by removing it and trying to blow through it. You should NOT be able to blow through it when it is out of the car. The only other thing that can cause those sort of symptoms is a leaking injector, but if that was the case the starting issue would happen even in the winter, hence why i'm confident it's your EVAP