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25 Mpg 06 Reg Mondeo


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hi all

my poor mondy is doing 25 mpg on the dash and the fuel gauge confirms this lol

i need to know what can cause this

i have used f super and i have uploaded a pic and i seem to be using a lot of diesel on idle

and how can i test my map sensor and what sensors can i test and which ones might have a problem

thanks a lot



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You seem to have three error codes stored - click the "read DTC" button and find out what they are.

Haven't done much with the F-Super but off the top of my head, Mass Airflow Sensor and EGR valve could be worth a look. But check out the error codes first as it'll likely point you in the right direction.

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hi thanks for the reply

the error codes point to alternator smart charge

and egr performance but i had blocked off egr valve

i was wondering if its the map sensor as it only reads about 10

or i might have a intake manifold air leak not sure but needed to know how to test the sensors map and maf



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As its an 06 mk3 its liable to be a Euro4 so that would account for the EGR code even though its blanked

It is easy to get "carried away" with the electronics/ error codes, although there is a "sophisticated" digital ECU / control system/s "underneath" that is a deisel engine (that have been around for 100 years) - the fault codes are only a guide/ tool, not a "be all & end all" - ive seen owners concentrating too much on the codes and not the engine itself or their eyes/ ears

Have you had the car a while? was the MPG always that bad?

has there been any changes to the car? - any work done to it at all etc?

is the car running ok? any exessive smoke?/ strange noises you never heard before?/ how is the performance - as good as normal?

When was the car last serviced? - a fresh air / fuel oil filter & change is a good start (if not done recently)

the breather deposits oily residue into the boost hoses and can gunge up the MAP sensor - worth cleaning it out - the MAF does not get as dirty and is delicate and may need special cleaner

The boost hose between the EGR valve and MAF pipe (front/ left EGR) often splits - (because of the realitive movement of the engine/ chassis) it can be hard to spot the split without taking the hose off - a split here (or any of the boost hoses) would account for the poor MPG

once you have sorted the fault it is worth ressetting your ECU (this should help MPG)

Also worth checking your brakes arnt binding (back brakes are bad for this) the tyres have plenty of air (40psi front 38 rear) and try to keep the weight down in the car if you can

25mpg is very poor for a mk3 and even round town/ going "beserk" i get at least 35mpg + - so there is very probably something wrong

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hi thanks for the reply

this is what i know

i brought the car as a fixer upper lol

it would not tick over right so i had injectors reconditioned got new codes and recoded using f supper all seemed fine it started first time no probs

it does sound like a diesel knock in there it revs drives ok picks up speed not to bad it has 100000 on the clock no smoke to worry about normal black

new ford fuel filter new oil filter and oil and air filter

i have cleaned the maf sensor it was dirty cleaned map sensor it was slightly oily pipes for inter cooler are oily

turbo seems ok no wobble or grooves in there

i have gave it a raz around down motor way and around town

the dash says 25 to 30 mpg but it has 1/4 of a tank of fuel i have put £50 and it says brim full

there is not much more i can tell you about it as i know nothing about its history

would a leaking inlet manifold gaskets cause this to be so bad?

and does the computer work the mpg off how much fuel is in the tank

does any one kn ow how the computer works out it mpg?

thanks a lot


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Daft question but have you tried resetting the trip computer? If it was running badly due to injectors before, then you'll be getting a skewed reading because of that. Put the display onto MPG and hold down the button below the display for 5s til it resets.

Then go for a drive. As a guide, my 2.0 55-plate TDCi is showing 52MPG on average at the moment.

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if there is a leak anywhere between the outlet of the turbo compessor to the inlet valves you can loose boost

inclucing any splits in the hoses, the intercooler, the joins, the gaskets (including the ones on the inlet manifold) the EGR valve etc etc

This means the turbo has to work a lot harder, reducing efficiency and/ or the loss of boost causes a loss of power - the injectors will be squirting as much fuel in as before but less boost/ air reducing power meaning the engine has to be worked harder using more diesel but with less power/ distance covered/ results

more smoke than normal would be expected though

brimming the fuel tank will not change the MPG

The ECU reads various sensors and calculates the instantanious and avarage MPG from this - whether there is a full tank of fuel or a 1/4 tank etc

an initial low avarage reading can drop/ hold the overall avarage down - for example if you were previously achieving 25MPG due to a fault, if the fault was fixed and you were achieving 50MPG the avarage reading would not suddely rise to 50mpg, but would gradually rise over time (eg 26, 27, 28 mpg) even though the car was achieving 50mpg

so the computer works out the AVARAGE mpg from the time the trip computer is reset - so if you reset the trip computer as BD has suggested it will "start afresh" and you may find you get a better MPG displayed

the engines' computers/ electronics are far more sophisticated than you might think - eg - it has a "learning" ECU, which actually "learns" your driving style, and other things (stuck on a dirty old transit diesel emgine!)

disconnecting the battery for 20 mins will reset the ECU (watch you dont loose your radio code) the ECU will "relearn" (eg the changes to the injectors etc), and may run better with better MPG after the reset

the oil in the intercooler/ boost hoses is normal, the engine breather injects a spray of oily droplets inbetween the airbox and inlet of the turbo compressor, this deposits oil from that point onwards, the oil can condense and collect inside the intercooler

When the engine gets older/ more worn it can produce more oil, the oil can mix with the carbon from the EGR system, forming an oily gloop, the oil can break down/ weaken the rubber in boost hoses over time too

some people fit catchtanks or breather filters to prevent this - remember the oil is from 1000s of miles

the inlet manifold would have to be very badly gunged up/ restricted to cause such a poor MPG, unlikely, IMO

the oil can also be from leaking turbo seals - best to keep an eye on the oil level dipstick

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