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

 

[Skylow]

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

Any idea where the vale is located? tried to find it, but i believe it is not visible in this engine...

 

[mty12345]

Any idea where the vale is located? tried to find it, but i believe it is not visible in this engine.... The pipe from it should go into the inlet manifold and the other pipe should be coming from the fuel tank along with the other fuel lines.

Edit: looking at some scrap engines, looks like this is it. So you'll need to remove the airbox as your inlet manifold is at the rear of the engine.

 

[Skylow]

Edit: looking at some scrap engines, looks like this is it. So you'll need to remove the airbox as your inlet manifold is at the rear of the engine.

View attachment 45829

Update...
So, i've changed the pre cat o2 sensor and nothing changed. Light still comes on.
Changed the EVAP valve wich had a defect, it would not close completly.
But even after that and clearing the error codes, after 20 or 30km the engine light still comes on. Still did not connect the OBD to check the error but i believe it is still the same. Strange it may appear, the light almost allways comes on on the exact same road and same direction, in 5th gear around 90/100km/h.
Don't know what else to do...

 

[mty12345]

Update...
So, i've changed the pre cat o2 sensor and nothing changed. Light still comes on.
Changed the EVAP valve wich had a defect, it would not close completly.
But even after that and clearing the error codes, after 20 or 30km the engine light still comes on. Still did not connect the OBD to check the error but i believe it is still the same. Strange it may appear, the light almost allways comes on on the exact same road and same direction, in 5th gear around 90/100km/h.
Don't know what else to do...

What brand was the O2 sensor? If it was some cheap one the mixture could well be out. Better to put the OEM one back in if so.

Need to scan the codes, could be something different. If the EVAP was faulty than that should have stopped the rich mixture code.

 

[Skylow]

What brand was the O2 sensor? If it was some cheap one the mixture could well be out. Better to put the OEM one back in if so.

Need to scan the codes, could be something different. If the EVAP was faulty than that should have stopped the rich mixture code.

Still did not changed back the o2 sensor to the OEM. The mechanic says the new one is no OEM but it is of a good brand. There are some graphs of short and ling term fuel trim at iddle and accelerating and the o2 readings.
The code that i'm getting is the P0172 (system too rich bank 1 sensor 1). Going to replace the o2 sensor in the next days and test again.
The MAP sensor is sending good readings. At least it goes up as i accelerate and is steady at iddle.
Edit: my PCV at the back of the engine is leaking some oil, not much but some. Did the oil plug test and it is not pushing or pulling air, so the vacuum is fine, but my idea is that there could be some oil leaking to the inside of the PCV causing the rich mixture readings... I say this because there is some oil vapors on the back of the car, so i believe there is oil going inside the combustion chamber...