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Engine backfires

Tiny
RICHARDQUINTO
  • MEMBER
  • 2002 FORD F-150
  • 4.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 119,000 MILES
When starting in the morning or if it sets for ten minutes the engine backfires through the manifold. After it starts it runs perfect no problem at all. If you park it for five minutes the same thing occurs. I have replaced the MAF, cleaned the pcv, fuel filter. Cleaned the throttle body and the IAC. After it starts you get a code P0171 and P0174. You can clear the code and it will not reappear until it starts again. Have any ideas?
thanks
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Monday, June 26th, 2017 AT 1:29 PM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
Hello,

This is a lean system trouble code and is caused by too much air int he system which can be caused by two things, first is the engine misfiring.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

the second is a vacuum leak.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run some tests and get back to us we are interested to see what it is.

Cheers, Ken
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Wednesday, June 28th, 2017 AT 5:58 PM

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