How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22750
Experience:  BEng hons Mech engineering, in auto industry 22 years
Type Your Car Question Here...
Matt is online now

I have some intermittent miss fire with fault codes showing

This answer was rated:

I have some intermittent miss fire with fault codes showing a super knocking fault on cyls 1 and 4 (2F76 & 2F79) as well as an injection cut out (2F7C). I also have an oxygen sensor after cat ageing fault (2D1E). Are these linked and if not what cmight be the cause of the misfire?


can you tell me what make, model, engine size and fuel type this is please?

also how many miles are on the car and when it was last serviced?

Customer: replied 1 year ago.
Hi, it's a Mini Cooper, 2010 with 85000kms on it. Not sure when it was last serviced as I've not long owned it. Didn't get a full service history with it.
Customer: replied 1 year ago.
Oh, and it's petrol.
Customer: replied 1 year ago.
Cooper S if that makes a difference to the engine?


to get those knock / misfire faults along with the o2 fault then I'd 1st say its worth checking the fuel pressure on a running engine as it should be about 3.0 Bar when measured at the fuel rail

if its low then you'll get fuel starvation , misfires, knocking and cataylst faults as you describe

and the 1st thing to try and rectify it would be a new fuel filter

Also replace the spark plugs if any of them fail this checklist:

You can also try spraying some water on the coil packs with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.

I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light

Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.

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 leans the engine out 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.

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 moving over your fingers

Customer: replied 1 year ago.
Wow! Really detailed reply and a lot to go on. Thank you. I was also thinking I could have picked up some dirty fuel so I will change the fuel filter as a matter of caution anyway. I've had the faults cleared and will see if it rears it's head again.

no problem

just get back to me on this post

Matt and 3 other Car Specialists are ready to help you