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I've got a 97 4WD Rav that I've been trying to get better mileage with for quiute a while now. I got a scan tool that runs on my plam pilot and I've found one thing that seems to be a problem, but can't determine what's causing it. Anytime I'm driving over 65mph it switches to open loop and my o2 sensor reads about 0.85v steady. I know it's supposed to switch to open loop during hard accel and when the engine is under a heavy load, but crusing on level ground @ 65mph doesn't seem like it should cause this. I got better mileage (23mpg) on a trip with mostly winding up and down through mountain passes than I did driving straight up the interstate (20mpg) @ 70mph. Any ideas what would cause it to switch over to open loop so easily? Oh yeah, I tried changing out the o2 sensor, but that had no effect at all.
 

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xosop said:
I've got a 97 4WD RAV that I've been trying to get better mileage with for quiute a while now. I got a scan tool that runs on my plam pilot and I've found one thing that seems to be a problem, but can't determine what's causing it. Anytime I'm driving over 65mph it switches to open loop and my o2 sensor reads about 0.85v steady. I know it's supposed to switch to open loop during hard accel and when the engine is under a heavy load, but crusing on level ground @ 65mph doesn't seem like it should cause this. I got better mileage (23mpg) on a trip with mostly winding up and down through mountain passes than I did driving straight up the interstate (20mpg) @ 70mph. Any ideas what would cause it to switch over to open loop so easily? Oh yeah, I tried changing out the o2 sensor, but that had no effect at all.
Plugged cat could be causing that.
 
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Do you know of any way to test the cat to see if it is plugged? As far as I know, the post-cat O2 sensor is there for that reason, to make sure the cat is working properly. I've been told that if the post-cat O2 reads kind of like a sluggish O2 sensor, slow waves, sticks high and low, that it is fuctioning properly. Mine seems to read just like that. Have I maybe been misinformed?
 

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xosop said:
Do you know of any way to test the cat to see if it is plugged? As far as I know, the post-cat O2 sensor is there for that reason, to make sure the cat is working properly. I've been told that if the post-cat O2 reads kind of like a sluggish O2 sensor, slow waves, sticks high and low, that it is fuctioning properly. Mine seems to read just like that. Have I maybe been misinformed?
Your cat could be restricted and the O2 sensor would still read properly. Unfortunatly there's no way to check it without taking it off, which probably won't cost that much at a muffler shop, it will have to be welded back on. When you are cruising at 65, are you in 5th gear at around 3500rpm?
 
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It's an auto, so I'd assume it's in 4th gear @ 65mph. Usually runs at around 2700 rpm @ 65 mph.
 
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