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Matt, Mechanical Engineer
Category: Ford
Satisfied Customers: 22913
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My 05 1.8 petrol mondeo has just failed the mot test on

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My 05 1.8 petrol mondeo has just failed the mot test on emissions. I have changed the cat, oil filter,air filter egr valve,air intake valve, o2 sensors checked the vacuum pipes but it has failed again on co emission.The readings are all over the place one min they are fine 10 seconds later they rocket sky high then down again .One min HC is over 1000 next test could show 90 lamba passes one test and fails 2 mins later.I do notice that no matter which o2 sensor I unplug or even both unplugged the engine management light does not come on. The car does have high mileage at over 200000 miles but was always serviced regularly.I did have a full diagnostic check done but nothing showed up


This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine 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 /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading

Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

Customer: replied 1 year ago.
I did check and change MAF also I took off inlet manifold and found a split rubber pipe from it to engine the HC readings did come down but still above fail rate. How do I get the fuel issues checked,ie the pressure and regulator


there should be a little schrader / tyre valve on the fuel injector rail so you can pop a pressure gauge on there with a running engine

it should read 3 bar

if it does then its OK

I'd also consider replacing the spark plugs as if you have a misfire going on then this will also put your emissions over

Customer: replied 1 year ago.
I did change spark plugs. Thanks Matt for all your help and a few things now for me to try and hopefully get a positive result
Customer: replied 1 year ago.
Should an unplugged o2 sensor not put on the EML when the car is started


yes disconnecting the o2 sensor would normally illuminate the check engine light

so I do wonder if there's a short in that sensor wiring loom thats both effecting the reading and fooling the ECU

so its well worth checking along the loom for hard sections and other damage

Matt and other Ford Specialists are ready to help you
Customer: replied 1 year ago.
I have tried everything you suggested so far except for the pressure test on injector bar as there is no schrader anywhere on the bar. Every other check is not showing any change to the problem,maybe its just down to a tired engine.I would still like to do the pressure test is there any other way to check it. Thanks


Yes if you look at the the rubber fuel lianfuel rail and where the rubber hose attaches then this hose can be detached and 'Tee'd' off into a pressure gauge

if you don't have this sort of equipment then any fuel injection garage can help

Customer: replied 1 year ago.
I have just taken out the spark plugs that the garage fitted and have noticed that 2 of the plugs are Motorcraft Platinum AGRF 22P1 One of the other plugs is NGK Motorcraft Platinum AGFS 22FE13J and the fourth one is NGK Motorcraft Laser Iridium AGF9 22IPJ could this be a major factor to the emissions problem.

That certainly won't help as there are 3 different heat ratings there

the 22FE13J are the correct rating

Customer: replied 1 year ago.
I also did a compression test and all 4 are showing 19bar 275 psi is this high or normal enough


thats all on the high side so I'd suspect that the combustion chambers are heavily carboned up and probably caked on the back of the valves too

so its worth trying some high grade fuel along with some injector cleaner to try and clean it up a bit

Customer: replied 1 year ago.
going to keep trying Matt without your help this would not be possible. Thank You, and will give review later


good luck


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Customer: replied 1 year ago.
I did rate you 5 stars the 23/8/16 I hope you got your share

much obliged