poor mpg and diagnostics

[durham4416]

i had my clio on the diagnostics last week because my toxic fume warning light came on for a few days, the diagnostics said that the upstream lambda was bust so i replaced it, the light has gone off but im still only getting 26.1 mpg with steady driving, i only sold my last car because it was a bit heavy on juice but even that was getting 27 mpg (bmw 330i) can you think what else would cause it, there is a slight blow from the backbox which is next on the 'replace' list when an exhaust comes up for sale, could this be a contributing factor?

also my esp light comes on after driving for about 20 minutes, the diagnostics came up with brake light switch as expected but iv replaced it with a genuine renault part and its still coming on, there is an led out inb the 3rd brake light, could this cause it as theres a break in the curcuit or is there a certain way to fit it. sorry for the essay

 

[Scott™]

What's your tyre pressures like? Seriously.

 

[durham4416]

yeah iv checked them, iv set them all to 33psi, still the same though

 

[maynard]

blowing of the exhaust may cause a slight loss in mpg but shoudln't be particularly noticeable.

with the bulb, replace the one that's out and then see if that clears the fault.

 

[piggoy]

Sorry but obvious, has it been serviced at regular intervals, spark plugs especially? I changed my plugs a couple of weeks ago after 40K on the same set and my average MPG has increased by over 5mpg.

Also are you sure the mpg reading is accurate? Are you actually using the amount of fuel the trip computer indicates? They are known for being a bit on the wild side. Maybe try and calculate it properly.

 

[iimushroomzii]

Coils? misfiring? Tyre pressures?

 

[maynard]

use this site to calculate it properly:

http://www.torquecars.com/tools/uk-mpg-calculator.php

 

[Fastchip]

diagnostics said that the upstream lambda was bust so i replaced it, the light has gone off but im still only getting 26.1 mpg with steady driving

Give it some time. Can take a while before the ECU relearns normal fuel trim values.

 

[durham4416]

thanks for all the comments, im going to give it a full service over the next couple of weeks so we shall see how that goes, there is no missfire, its running fine, (there wasnt a missfire when the toxic fume warning light was on either), its running fine, apart from rubbish mpg. ( i wouldnt mind if these cars only got 26.1 mpg but people on here get 35 lol

 

[durham4416]

also how do you disconnect the 3rd brake light when you pull it out, and is there a special way of fitting the brake light switch, do i just stick it in a twist it, job done or am i missing something