kkspeed

Is it worth changing the rear (after cat) O2 sensor on my 1997 Hardbody
(4 cyl, auto, x-cab)?

I heard different opinions on its affect on gas mileage.

I'm trying to get the best gas mileage out of the truck and changed all the basic tune-up parts (NGK plugs, cap, wires, rotor, set timing, clean throttle body, synthetic fluids. etc.....).

I currently get 22.5 MPG on the highway.

kkspeed

I forgot to mention that I changed the front O2 sensor with the tune-up parts.

1997XETruck

Sounds like you're getting pretty good gas mileage for the truck... I wouldn't mess with it unless it's checking bad. I replaced my front one to get from 16-18MPG to what you're getting now.... I think you've gotten to "as good as it gets."

Heath

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1997 Nissan XE Truck - 133,000 Miles
1990 Infiniti Q45 - 91,000 Miles
2005 Infiniti G35 Sedan - 34,000 Miles

88pathoffroad

I'm of the opinion that if you have the $$ on hand and it's never been replaced, do it. If not, it'll prolly go out on you later and you'll have to do it anyway. Old O2 sensors are notorious for giving bad gas mileage cause they've been fouled up for so long.

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'88 Pathfinder: 6" of lift, 33x13.50 Swamper LTB's, Rancho 9000's, L&P Stage 3 steering system, K&N, Pacesetter headers and 2.5" exhaust, Lock-Right locker, 110A alty and electric fan swap, dual batteries, 700W+ worth of PIAAs, etc.

mightymouse

I have emissions testing here, and I'm thinking if my 02's were going out, my truck would get worse, and since i'm passing with flying colors, I should be fine. Would that be a correct assumption?

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The only way to achieve the limits of the possible is to go beyond them into the impossible - unknown

1997XETruck

The front O2 sensor is actually the one that controlls the fuel mixture (or at least has a hand in it) while the rear is more there as a "check" to see that the catalytic convertor is doing it's job. O2 sensors tend to get sluggish (fewer lean/rich/lean/rich flips in a 10 sec. period) so that's the idea of replacing them before a complete failure. I haven't worried about the rear since it doesn't really control anything - but a sluggish front sensor can cause a rich fuel mixture... bad gas mileage or melted cats.

Heath

__________________
1997 Nissan XE Truck - 133,000 Miles
1990 Infiniti Q45 - 91,000 Miles
2005 Infiniti G35 Sedan - 34,000 Miles