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Misfire and codes P0420 and P0171

Tiny
WANDAANDBUDDY
  • MEMBER
  • 2007 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
It has had the catalytic converters removed and the exhaust pipe put back in place. It has an exhaust manifold leak. What is causing it to have a misfire and run so rough? What can I do to fix this problem?
Friday, June 17th, 2022 AT 3:59 AM

2 Replies

Tiny
WANDAANDBUDDY
  • MEMBER
  • 9 POSTS
If I put in spark plug non fouler will this help any with misfire?
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Friday, June 17th, 2022 AT 11:16 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Just to be clear, you have removed the catalytic converter. If that is the case, you are going to have to ignore the cat efficiency code. If you don't have them then the o2 sensors are not going to see the reduction in emissions so it is going to say it is not efficient.

The fact that you have this could be causing the lean code as well because it is thinking it needs to lean it out to compensate for the rich exhaust.

However, the main reason for the P0171 is a vacuum leak so we should start with this.

Here is a guide that will help with this:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

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

Once we know this info, we will have a better idea what direction to go. So let me know what you find. Thanks
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Friday, June 17th, 2022 AT 7:03 PM

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