Low power and poor mpg problem.

[xreyuk]

Since I bought my Seat Leon 1.6TDI CR, I have been having varying fuel consumption results. I was told to adapt my driving style, and that has certain helped, however, I definitely think there is a problem with the car.

The problem I've noticed, is if I start the engine from cold, and let it get up to temperature, it NEVER reaches full efficiency, and it feels like an engine with 80BHP instead of 105BHP.

If I then stop for around 10-15 minutes, and turn the engine back on (whilst it's still warm), the MPG takes a massive jump up, especially on the live data display. The power also feels like it should. This is how I would have thought the car would perform all of the time.

I decided to do a test. I started the engine cold, got it up to temperature and went to the motorway nearby. I reset the trip when I reached 70mph, and stuck cruise control on. I did a 10 mile journey to the end of the motorway, made a note of the reading, and then did the exact same thing back up the other side (waiting until 70mph to reset the trip etc). I averaged the two readings. at 52.9mpg.

I then stopped the engine for 20 minutes, got a cup of tea etc. I then did the exact same test on the exact same bit of motorway. The average mpg this time around was 65.4mpg. A MASSIVE jump.

It's also returning on average 10mpg higher in urban driving when started warm, as opposed to being brought up to temperature and the trip reset

Do you have any idea what could be causing this? Someone on another forum said they noticed similar symptoms in a Mondeo with a faulty temperature sensor/thermostat. I've also read that it could be the MAF.

I have fully activated VAG COM, so if anyone could suggest anything I could be maybe monitor to take to SEAT, because, as usual, I'm just getting the old 'we're not having an issue when we drive it'. The car is under warranty so without an error code or some sort of evidence I don't know how far I'll get.

Thanks guys

[KevinA3DSG32]

Always take the mpg readings with a massive pinch of salt. The only way to measure it is by brim to brim tank fills and elapsed miles. All my VAG cars have had wildly fluctuating readings.

[daydotz]

lots of discussions about poor fuel consumption with the 1.6tdi try briskoda & seatcupra.net

Edited by daydotz on Thursday 14th June 17:32

[xreyuk]

[quote=daydotz]lots of discussions about poor fuel consumption with the 1.6tdi try briskoda & seatcupra.net

It's not a poor fuel consumption problem though, because when started warm, the engine is fine, easily does around 60mpg in town, and late 60s to 70mpg on the motorway.

[KevinA3DSG32]

IF you are absolutely sure that it varies from cold start even when warm, to warm start then I would get it checked out for the cold start settings switching off when warm.

[xreyuk]

KevinA3DSG32 said:

IF you are absolutely sure that it varies from cold start even when warm, to warm start then I would get it checked out for the cold start settings switching off when warm.

Thanks. What do you mean about the cold start settings switching off? Is there a certain set of instructions that are supposed to change when the engine reaches temperature?

Is this checkable with vag com or by a dealer only?

Thanks.

[KevinA3DSG32]

Hi, The engine fuelling settings are necessarily different when starting from cold (like a choke on a carburettor). This will enrich the mixture until the engine has warmed to normal operating temperature. If the engine ECU is not switching the mapping back to 'normal' from 'cold start' the engine would be running rich, i.e. extra fuel which would account for your symptoms. I have no idea how you would check this, probably needs a specialist to have the car overnight so they can do a cold start.

[xreyuk]

KevinA3DSG32 said:

Hi, The engine fuelling settings are necessarily different when starting from cold (like a choke on a carburettor). This will enrich the mixture until the engine has warmed to normal operating temperature. If the engine ECU is not switching the mapping back to 'normal' from 'cold start' the engine would be running rich, i.e. extra fuel which would account for your symptoms. I have no idea how you would check this, probably needs a specialist to have the car overnight so they can do a cold start.

Thanks for the information, I will bear that in mind when I go to check.

The other possibilty I thought about the thermostat was sticking, but I monitored coolant temperature and it seemed to be correct.

I didn't realise a car ECU did this, so I'll get them to check it.

[Dr G]

Still possible it's a temperature/sensor/thermostat issue; the temp gauges sit at 90 even when the engine is ~20 degrees either side.

[Jon999]

Is this one of the affected VW group engines?