Cupra 300 over fueling

[Beef46]

Hi everyone. First post here so be gentle!

So i have owned a 2018 Leon Cupra 300 ST 4 drive since January and I absolutely love it.
However recently the car has developed a significant drink problem!

Normally when I fuel up, I get a theoretical range of 385 miles, and i usually refuel at around 330 miles with the trip computer giving an average of around 30-32mpg. When i took the car to Yorkshire a few days after I bought it, in January it averaged 38mpg which was great.
A few weeks ago a drove over to the Netherlands for the Dutch Motogp and was interested to see how it would do on fuel. Well, from start to finish it was absolutely terrible with it struggling to average around 25-27mpg.
And likewise since ive been back and doing my normal driving it is still really bad. So much so that when I fuel up now, it only gives me a theoretical range of 295 miles. The last time I refuelled was after 232 miles which is absolutely terrible. Around 24 mpg seems to be the average now! That's worse than my old Focus ST that had the 2.5 five pot, which is renound for being thirsty!

The car has no symptoms at all. It drives and performs normally which is really odd.
Today it went back to the main dealer as its still under warranty. Well to say they were useless was an understatement. They did no fault diagnosis whatsoever other than plug a laptop in and scanned it for codes - which there wasnt any, so then proceeded to say there was nothing wrong, implying I was lying!

Anyway, without waffling on too much, have any of you knowledgeable lot ever experienced such over fuelling with no symptoms and if so what was the cause?

From the research I've done I'm thinking its got to be either injectors, fuel pump, pcv valve, cam sensor, maf sensor, ecu???

As i said its still under warranty so I am fighting with the dealer to get them to do some good old fashioned fault finding which they are pushing back on.
Think im going to have a bit of a fight on my hands! Bloody hate main dealers!!

I really hope someone on here has experienced something similar and can offer some possible solutions.

 

[James_R]

If the car was over fuelling to the point it was affecting the emissions and fuel economy, then there would be accompanying fault codes to back the symptoms up.

Have you considered non engine related issues being the cause? Such as low tyre pressures, sticking brakes, etc?

With the car being covered by an extended warranty plan (basically an insurance policy that covers sudden component failure), you are generally responsible for covering the diagnostic fee until the cause is located and approved by the warranty provider.

 

[mty12345]

If it was 'overfueling' then there would be a host of fault codes.

Low MPG could be caused by weight/load, poor tyre pressures, high speed, stop/start driving, inclines etc etc.

 

[Beef46]

If it was 'overfueling' then there would be a host of fault codes.

Low MPG could be caused by weight/load, poor tyre pressures, high speed, stop/start driving, inclines etc etc.

This is why it's so odd that there are no warning lights or fault codes.
Tyre pressures are checked regularly and my driving style hasnt changed.

When I went to the Netherlands it was literally a 1200 mile trip travelling on motorways at 70-75 mph. From Calais right up to the Netherlands and back there were literally no inclines - it was pretty well completey flat, so the car was under no load at all.

Since ive been back ive just been doing my usual driving consisting of my commute to work, a bit of town driving and some A road / motorway driving.

Nothing has changed apart from the fact the car is using considerably more fuel. For example, my commute to work involves me being sat behind multiple buses heading out to Hinkley Point C. Its the same every day. When I getbto work the car generally says ive averaged 35-37 mpg for that trip. Now - for exactly the same trip the most ive seen is 27 mpg. It really is bizarre and a real head scratcher, hence why I've come here in the hope that someone has experience of this.