Not an E10 post, a problem with my car.

A couple of months ago, out of the blue, my car started becoming less economical, about 10-15% worse. I noticed because I record every fill up for other reasons.

I knew it was not the colder weather but there were no symptoms I could blame it on.

However I have noticed that the idle has become higher on startup and is generally a little erratic in behaviour. It doesn't seem any different when driving, just the idle so something is not running right.

What should I be checking before I take it to a mechanic with no info other than its using more petrol?

(Air filter looks ok and its a fairly basic 16v Japanese petrol engine)

Edited 6 February, 201412 yr by 'daiking'

Could it be weather related? Motorway driving in the seemingly constant winds has battered my economy down from +60mpg to low 50s just lately. This last week especially i've used more fuel than I would normally, I drive around 25 miles on open stretches of the M6. Just a thought.

My fuel economy has been up and down between 51-57mpg (which to me is a large margin considering my routes vary very little) since the end of summer and I'm pretty sure it's down to how windy it's been.

Is this a comparison from the fuel use you were monitoring last winter, 

or only some period during this past Summer?

 

Is there a inline fuel filter that needs changing.

& Where do you buy your petrol?

 

In Scotland and the North of England Winter Spec Fuel starts leaving the Depots for filling station tanks,

That is until the end of March.

It may start being distributed later down south.

 

So that is the Winter Anti Waxing Diesel, but also the Winter Formula Petrol, which is less Hygroscopic.

(i find this to give better economy, especially with Tesco Momentum 99 which is always minimum 99 ron,

but can be of a higher octane than the minimum, especially at Winter Spec time, & only 5 pence a litre more expensive.)

 

Winter spec petrol should not reduce your economy, but if you are watching your cars consumption,

starting up and defrosting, adjusting your tyre pressure to the different ambient temp, and all the rest,

you should easily know if it effect your vehicle for the worse or for the better.

 

Tyre pressures are often the biggest factor on fuel economy.

Check oil and tyres - K.I.S.S.

 

Been carrying anything different, passengers?

Different roads.

 

Could be something as simple as the windy weather we've been having.

I've noticed a difference in coming to work and going home mpg. To work with wind - to home against wind almost 10mpg difference.

Given how the car has behaved over 7 previous winters, I'm saying its not the weather nor anything simple like tyre pressure or car load.

It just dropped in mid-October and has not come back yet.

So mid October is pretty near the 15th of October when the Winter Spec Petrol starts leaving the Depots.

 

So what petrol do you put in, supermarket 95 ron or something else.

 

What car,

what age,

what mileage,  

Have you actually checked the Tyre Pressures since October,  

 

Over the 7 previous Winters it was newer, and lower mileage,

What Servicing & Maintenance does it get now?

 

?? Does it need New Spark Plugs?

Does it have ignition Coil Packs and could one be on its way out or already ****'d

 

Not getting at you, but you asked a question, dismiss the replies but give little information.

 

Maybe it does not like the petrol it is getting since mid October, but if you use different Filling Stations then that is maybe not it.

 

http://michelin.co.uk/tyres/learn-share/care-guide/cold-weather-tips

Tyre Pressures and cold weather checking, but if its not cold where you are, maybe not relevant.

In that case have you checked the lambda sensor? Seems to pre-date the bad weather and normally a drop in economy is a sign this unit is not the full shilling. 

Winter Spec Fuel, high winds and even though the air filter looks clean it may well be starting to clog up (More than 15k since it was last changed?).

 

After that I'd start looking at the sensor relating to the coolant temperature and exhaust management.

I take it you've done your oil services as expected and the engine oil hasn't got all thick and heavy too.

So mid October is pretty near the 15th of October when the Winter Spec Petrol starts leaving the Depots.

So what petrol do you put in, supermarket 95 ron or something else.

What car,

what age,

what mileage,

Have you actually checked the Tyre Pressures since October,

Over the 7 previous Winters it was newer, and lower mileage,

What Servicing & Maintenance does it get now?

?? Does it need New Spark Plugs?

Does it have ignition Coil Packs and could one be on its way out or already ****'d

Not getting at you, but you asked a question, dismiss the replies but give little information.

Maybe it does not like the petrol it is getting since mid October, but if you use different Filling Stations then that is maybe not it.

http://michelin.co.uk/tyres/learn-share/care-guide/cold-weather-tips

Tyre Pressures and cold weather checking, but if its not cold where you are, maybe not relevant.

My car is a 2006 Mazda3 with a 1.6 litre 16v petrol engine and covered 97,000 miles from new under my ownership. It has been serviced to the manufacturer’s specification, annual/12,500 miles +/- 1000 miles. Last service in July 2013 and although not specified, it had its plugs changed.

All 4 tyres were changed for Goodyear Efficientgrips in September 2013 and for a couple of tanks of fuel seemed to give slight improvements in economy. I haven’t forgot about the tyre change but the early impressions and in comparison to previous tyres, I am not wholly convinced that a highly regarded branded ‘green’ tyre is the cause of this reduction. I have checked the air filter and the tyre pressures and both are satisfactory. The battery was changed for a Bosch S4 item in December 2013.

I have comprehensive fuel records dating back to the car’s purchase, as new so I immediatley noticed the fall in consumption on a brimmed tank to tank basis. This is by any comparison you want to make, seasonal, YoY, etc. Under normal driving conditions, I had noticed (via the OBC trip functions) that I was not achieving the economy I expected nor could I improve it when trying.

Its only now when I have noticed another symptom (engine idle) that I am pursuing the problem. I don’t have a generic ODB code reader to see if any faults are being recorded. As I’m sure you well know, going to the dealer and saying my car is using a bit more petrol, can you have a look will only likely end up in a diagnostics bill and a shrug as to the cause from the dealer.

It looks like I'll continue to montior it unless it throws a spanner in the works.

The tyre change can well be the culprate to some degree,  

& even if not the Tread or improved traction after the 'Greenness' Release Compound has gone, & Traction is greater,

& even if they are the same size tyres. by the Numbers,

are they perhaps a little different in the Total Diameter/Circumference, so that gives a little difference in miles covered or MPG.  

Minimal difference, but a factor that always needs considered.

(you measure old and new side by side and can sometimes see quite a difference.)

 

But that does not have anything to do with what you mentioned about the engine.

 

Maybe change where you buy your fuel,

but do not just take it as a given the new spark plugs are right because they can fail prematurely.

I would get the Diagnostic done to see if there has been a misfire, because a coil can cause the poorer economy.

Are the spark plugs the right ones or gapped correctly?

Seems a bit of a coincidence that you change the plugs and economy tanks shortly after.