P0303 DTC code can feel it misfire

Tiny
IAN MCCRIMMON
  • MEMBER
  • 2009 FORD FLEX
  • 3.5L
  • V6
  • AWD
  • AUTOMATIC
  • 120,000 MILES
Have a P0303 DTC code pending. I can feel misfire and the check engine light flashes under load. Have replaced COP and plugs as well as the number three fuel injector with no improvement.
Monday, December 12th, 2016 AT 10:38 AM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,859 POSTS
Hey IAN,

I would pull the number three cylinder spark plug and do a compression test to see what it is, also check the condition of the spark plug to see if its fouled black.

Here is a guide to help,

https://www.2carpros.com/articles/how-to-test-engine-compression

Please run this test and get back to us so we can continue helping you.

Best, Ken
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Monday, December 12th, 2016 AT 9:21 PM
Tiny
IAN MCCRIMMON
  • MEMBER
  • 3 POSTS
I inspected the plugs on all and there is nothing to report as far as fouled plugs. All look fine. The compression test is next-a mechanical failure in this cylinder will be the last straw!
The one thing I saw while looking online is that transmission or driveline issues can mimic a misfire but how can they trip a DTC? It needs front brakes badly.
Speaking of DTC my wife took the vehicle to work and back and my scanner showed two codes, one fault and one pending both for P0303. Also the check engine light was on; up until now it never showed a check engine light.
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Tuesday, December 13th, 2016 AT 4:09 AM
Tiny
KEN L
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Please let us know what you find so it will help others.

Best, Ken
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Tuesday, December 13th, 2016 AT 10:38 AM
Tiny
IAN MCCRIMMON
  • MEMBER
  • 3 POSTS
Broke down and took it to a repair shop of a friend we know-turns out I broke the porcelain on spark plug #3 during the install. Most likely due to over tightening-I believe the torque spec is 133 in/lbs. I neglected to use a torque wrench and simply over tightened them.
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Friday, December 16th, 2016 AT 5:03 PM
Tiny
KEN L
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I happens, I have broken my fair share of spark plugs. Good find thanks for getting back to us with the fix, Please use 2Carpros anytime we are here to help.

Best, Ken
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Friday, December 16th, 2016 AT 9:57 PM

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