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Matt
Matt, Mechanical Engineer
Category: Ford
Satisfied Customers: 20588
Experience:  BEng hons Mech engineering, in auto industry 22 years
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have 05 plate mondeo 115 brake diesel 120 k on clock regularly

Customer Question

have 05 plate mondeo 115 brake diesel 120 k on clock regularly serviced recent new dmf fuel consumption used to average 50+mpg now down to 42 has happened gradually over last 6 months would appreciate words of wisdom cheers Brian
Submitted: 3 years ago.
Category: Ford
Expert:  Matt replied 3 years ago.
Hello

This could be a number of things:
Incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will be leaving the car constantly ' on choke' and not reducing the fuelling as the engine warms - so unplug the sensor and clean the contacts on both sides with some switch / electrical cleaner ( not WD40) and inspect the wiring for any signs of damage to the insulation especially where it runs over other components and through the bulkhead- if this doesn't help consider replacing the sensor as they're not expensive




Air leak at the mass airflow meter -
Any air dragged after the meter isn't 'seen' by the ECU and so not compensated for, causing rough running.
Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.
Binding brakes:
Check that all the wheels can be turned freely by hand, and free off any sticking calipers
Incorrect wheel alignment:
Check all the tyres for signs of uneven wear if it has any then get it checked out at a place that does 4 wheel alignment not just front tracking and ensure tyres are pumped up to their reccommended maximum
Injectors are clean and not dribbling - add a bottle of injector cleaner to the tank

Use good quality fuel - from my own findings its worth paying the extra for BP or shell as typically you'll get another 10% fuel saving which outweighs the cost over supermarket fuel.

And the biggest thing is driving style, by not labouring the engine ( too high a gear up hills etc) and not accelerating hard away from the lights etc you can usually improve things by another 25-30% or so.

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