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
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21113
Experience:  BEng hons Mech engineering, in auto industry 22 years
12772297
Type Your Car Question Here...
Matt is online now

I have some intermittent miss fire with fault codes showing

Resolved Question:

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?
Submitted: 10 months ago.
Category: Car
Expert:  Matt replied 10 months ago.

Hi

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 10 months 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 10 months ago.
Oh, and it's petrol.
Customer: replied 10 months ago.
Cooper S if that makes a difference to the engine?
Expert:  Matt replied 10 months ago.

Thanks

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

Expert:  Matt replied 10 months ago.

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

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

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

http://www.noidlight.com/

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 9 months 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.
Expert:  Matt replied 9 months ago.

no problem

just get back to me on this post

Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21113
Experience: BEng hons Mech engineering, in auto industry 22 years
Matt and other Car Specialists are ready to help you

What Customers are Saying:

 
 
 
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil
< Previous | Next >
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil
  • Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible. Charles
  • As a single woman, I really appreciate an excellent and affordable opinion.
    Thank you Geordie, I will not hesitate to contact justanswer in the future!
    Sue
  • Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, Frank...you do indeed know your stuff. Jim
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C.
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex
 
 
 

Meet The Experts:

 
 
 
  • Greg

    Greg

    Technician

    Satisfied Customers:

    1067
    Automotive diagnostic tech
< Previous | Next >
  • http://ww2.justanswer.com/uploads/IN/indytech/2013-8-8_102717_SantoDomingo146598x6402.64x64.jpg Greg's Avatar

    Greg

    Technician

    Satisfied Customers:

    1067
    Automotive diagnostic tech
  • http://ww2.justanswer.com/uploads/35/350matt/2012-6-7_182356_matsavatr.64x64.jpg Matt's Avatar

    Matt

    Mechanical Engineer

    Satisfied Customers:

    4197
    BEng hons Mech engineering, in auto industry 22 years
  • http://ww2.justanswer.com/uploads/TE/techmachine/0601821347169_717372168_8940977_39623330_o.64x64.jpg Ross's Avatar

    Ross

    Diagnostic and repair technician

    Satisfied Customers:

    452
    Licensed diagnostic and repair technician
  • http://ww2.justanswer.com/uploads/RO/RobMechanic/068.64x64.JPG Rob's Avatar

    Rob

    ASE Certified Technician

    Satisfied Customers:

    82
    30 years trade experience
  • http://ww2.justanswer.com/uploads/UK/ukiaibal/2012-11-9_205920_SAM0109.64x64.JPG uk_iaibal's Avatar

    uk_iaibal

    UK Car Mechanic

    Satisfied Customers:

    1
    Verified Car Mechanic.
  • http://ww2.justanswer.com/uploads/NA/nabilc/nabilc_avatar.64x64.jpg Billy's Avatar

    Billy

    Trainer/ Master Technician

    Satisfied Customers:

    38
    Trainer 8+ years, master tech. 10+ years, SAE member
  • http://ww2.justanswer.com/uploads/MI/mikeamechanic/2013-4-2_175558_photo.64x64.JPG Mike Kelly's Avatar

    Mike Kelly

    Auto Service Technician

    Satisfied Customers:

    1256
    17 years experience as an auto mechanic, foreign and domestic. 5 years running my own repair business.