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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 23082
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My w reg astra 1.4 eco engine has failed emissions test

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my w reg astra 1.4 eco engine has failed emissions test again three years running even after new cats previous year. CO levels too high. what else is causing this please?
Customer: replied 1 year ago.
forgot to mention that the oxygen sensor was replaced two years ago and the timing belt about 45000 miles ago


This is could beincorrect 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

Check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

One other thing is to ensure that you're running on the correct grade of engine and gearbox oil as if its too thick or overfilled this will really hurt the fuel economy

I'd also check the fuel pressure at the injector rail

if its too high it will be over fuelling

Matt and other Car Specialists are ready to help you
Customer: replied 1 year ago.
Thank you matt, just wonder what experience you have on the Astra range? That would help me greatly in the best way to go forward.
Thanks again


I've worked on a few in the past

do you need any further help?

Customer: replied 1 year ago.
Thanks Matt, I probably will need more help but it wont be till next weekend because I am travelling to work in Barnstaple for the week so wont have any tools with me or anywhere to do the work. thanks till then