MISFIRE PO303

  • Tiny
  • Dutrio
  • 2010 HYUNDAI I20
  • 15,000 MILES

The car has developed a misire on cyl 3 no other codes only p0303.
Swapped the sparkplug around also swapped with a working Ht lead from another car, swapped coils around, metered the injectors all the same reading.
No aparrent faults however the vehicle continues to misfire when cold or hot above and below 2000 rpm but never misfires when at idle and not under load. Any ideas?

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Tuesday, May 1st, 2012 AT 11:09 AM

8 Replies

  • Tiny
  • Mhpautos
  • EXPERT
  • 30,743 POSTS

Have you done a comp test? Just to prove that is ok.

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Tuesday, May 1st, 2012 AT 11:32 AM
  • Tiny
  • Dutrio
  • MEMBER

Yes compression test all seem fine on all cylinders, no starting issues either. And thxs for the quick response.

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Tuesday, May 1st, 2012 AT 11:51 AM
  • Tiny
  • KHLow2008
  • EXPERT
  • 41,984 POSTS

If engine valve rockers are not hydraulically operated, have the valve cleaances checked.

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Tuesday, May 1st, 2012 AT 1:05 PM
  • Tiny
  • Dutrio
  • MEMBER

Excellent response thxs again I will certainly check the valves however I do feel its more electrical perhaps than mechanical, due to the random nature of the misfire.

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Tuesday, May 1st, 2012 AT 1:57 PM
  • Tiny
  • KHLow2008
  • EXPERT
  • 41,984 POSTS

You have substituted all the electrical components most likely to cause the misfire and it did not solve the problem so it could be mechanical faults that are causing the misfiring.

Did you swap the injectors?

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Tuesday, May 1st, 2012 AT 3:23 PM
  • Tiny
  • Dutrio
  • MEMBER

Having looked at the fault a little deeper the mystery of the misfire deepens as the misfire only occurs whilst the vehicle is under power i.E clutch engaged and been driven and never when its simply been held at Any rpm without load.
Injectors have been tested but not swapped as suggested as the fuel appears not to be burnt when the misfire occurs according to the colouration and odour of the cyl 3 spark plug.

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Wednesday, May 2nd, 2012 AT 1:34 AM
  • Tiny
  • ASEMaster6371
  • EXPERT
  • 25,554 POSTS

Above 2500 could be a valve train issue if all the components you tested were verified.

With the low miles, isnt this under factory warranty?

Roy

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Wednesday, May 2nd, 2012 AT 2:44 AM
  • Tiny
  • Djcl
  • EXPERT
  • 786 POSTS

Attacha vacuum guage to the engine see if its pulling 20 in of vacuum @ idle and then @ 3000 rpm. This is a quick test.

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Wednesday, May 2nd, 2012 AT 2:56 AM

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