# Gas mileage question

**URL:** <https://community.cartalk.com/t/gas-mileage-question/76330>\
**Category:** Maintenance/Repairs\
**Tags:** s-15jimmy, gmc\
**Created:** [December 25, 2012, 9:55pm UTC](https://community.cartalk.com/t/gas-mileage-question/76330 "2012-12-25T21:55:55Z")\
**Posts on this page:** 6\
**Page:** 2

<div class="post-metadata">

**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\
**Post date:** [December 29, 2012, 12:22am UTC](https://community.cartalk.com/t/gas-mileage-question/76330/21 "2012-12-29T00:22:14Z")

</div>

“can the richness be leaned out?”

In a modern car that amounts to fixing the fault that’s causing it to run rich.  
Typically a tired O2 sensor.  
But you don’t know if that’s the issue with your vehicle.

---

<div class="post-metadata">

**Author:** ![FordMan1959](https://avatars.discourse-cdn.com/v4/letter/f/ea666f/32.png) [@FordMan1959](https://community.cartalk.com/u/FordMan1959)\
**Post date:** [December 30, 2012, 4:44am UTC](https://community.cartalk.com/t/gas-mileage-question/76330/22 "2012-12-30T04:44:39Z")

</div>

I too would suspect a possible bad 02 sensor. I’ve seen bad 02 sensors cause as much as 25-35% drop in fuel mileage. Might also be a bad ECT sensor causing the system to stay in open loop too long or all the time, or a brake dragging.

---

<div class="post-metadata">

**Author:** ![PVTodd](https://avatars.discourse-cdn.com/v4/letter/p/b782af/32.png) [@PVTodd](https://community.cartalk.com/u/PVTodd)\
**Post date:** [December 30, 2012, 11:51am UTC](https://community.cartalk.com/t/gas-mileage-question/76330/23 "2012-12-30T11:51:16Z")

</div>

Thanks man. I’ll replace it just to be on the safe side. Is it an easy job to replace it?

---

<div class="post-metadata">

**Author:** ![rocketman](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@rocketman](https://community.cartalk.com/u/rocketman)\
**Post date:** [December 30, 2012, 9:34pm UTC](https://community.cartalk.com/t/gas-mileage-question/76330/24 "2012-12-30T21:34:02Z")

</div>

What would happen if you just disconnected the O2 sensor? Run rich or lean? Never thought of that before, just wondering. Rocketman

---

<div class="post-metadata">

**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\
**Post date:** [December 30, 2012, 9:58pm UTC](https://community.cartalk.com/t/gas-mileage-question/76330/25 "2012-12-30T21:58:37Z")

</div>

@rocketman, if the O2 sensor was disconnected, the PCM would go into open loop.  
Then you’d definitely see lousy fuel economy.

---

<div class="post-metadata">

**Author:** ![PVTodd](https://avatars.discourse-cdn.com/v4/letter/p/b782af/32.png) [@PVTodd](https://community.cartalk.com/u/PVTodd)\
**Post date:** [December 30, 2012, 11:19pm UTC](https://community.cartalk.com/t/gas-mileage-question/76330/26 "2012-12-30T23:19:57Z")

</div>

Hey Guys, on my 1991 Jimmy is there more than one (1) o2sensor?

[Previous page](https://community.cartalk.com/t/gas-mileage-question/76330.md?page=1)