O2 sensor diagnosis?

Tiny
TWOZZIE
  • MEMBER
  • 1997 LAND ROVER DEFENDER
  • 4.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
1997 Defender failed CA smog due to rich mixture at idle and gave code P0176. Ran live diagnostics on the sensors and have results but cannot determine if they are ok or not.
Thursday, December 4th, 2025 AT 5:25 PM

7 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,591 POSTS
So it looks like you may have a fuel injector that is stuck open or leaking, I would remove all spark plugs and look for the one that is dark/black in color, this will be the cylinder that is having the issue.

P0176 on this model - Fuel Composition Sensor / Fuel Mixture Too Rich at Idle.

Please go over this guide as well, it shows what all can create a rich mixture code.

https://www.2carpros.com/articles/why-an-automotive-engine-will-run-rich

Please upload an image or a short video in your response of the spark plugs so I can see, be sure to keep them in order.

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Friday, December 5th, 2025 AT 11:40 AM
Tiny
TWOZZIE
  • MEMBER
  • 10 POSTS
Hi Ken, first off thank you so much.
Plugs out as per pictured. Only one, cylinder 8, looks black with gunk on it.
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Saturday, December 6th, 2025 AT 12:39 PM
Tiny
KEN L
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Alright! yep #8 does not look good, lets do a compression test to make sure the cylinder is okay, then we can replace the fuel injector which should fix the problem. Here is a guide to help.

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

Let me know what the reading is.
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Sunday, December 7th, 2025 AT 11:28 AM
Tiny
TWOZZIE
  • MEMBER
  • 10 POSTS
Ok, need to get a pressure gauge and the injector is on order. :)
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Sunday, December 7th, 2025 AT 12:04 PM
Tiny
KEN L
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Nice, you can rent a gauge set for free from AutoZone to do the compression test.
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Monday, December 8th, 2025 AT 7:51 AM
Tiny
TWOZZIE
  • MEMBER
  • 10 POSTS
Ken, installed new plugs and air filter. Poured a can of injector cleaner in the tank and it passed smog with flying colors today. Appreciate the help.
Cheers, Ewan
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Wednesday, December 17th, 2025 AT 4:21 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,591 POSTS
Yes!! Please use 2CarPros anytime we are here to help. Can you please leave us a rating?

https://g.page/r/CZdEnyCkGgm6EB0/review

and

https://www.sitejabber.com/reviews/2carpros.com

Thank you :)
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Thursday, December 18th, 2025 AT 9:39 AM

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