Working o2 sensors = worse mpg??
12-14-2010, 01:37 AM
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Working o2 sensors = worse mpg?? Ever since I bought my 98 z28 about a year ago, the service engine soon light has been on due to no activity in both front o2 sensors. I replaced the sensors and reset the SES, still no activity... SES came back on. At that point I pretty much just forgot about the problem because the car still ran fine... although it only got about 16.5 mpg highway.
Well the other day I was under the car and noticed the last owner had the rear o2 sensor harnesses plugged into the front o2 sensors (rear o2 sensors had been tuned out). I found the front o2 harnesses jammed up in the engine bay. I plugged the front o2 harnesses into the front o2 sensors like they should have been. Reset the SES, and it has not come back on since. I was expecting to see an increase in gas mileage... but it has actually dropped to about 13.5 mpg highway (was getting 16.5). I've filled up the tank several times since and it's never been above 13.5 mpg of highway driving. I've never heard of working o2 sensors decreasing the mpg compared to non-functioning o2 sensors. The car has a large cam and is running rich because it is untuned, but it should be able to get at least 20mpg highway. Any ideas?
Well the other day I was under the car and noticed the last owner had the rear o2 sensor harnesses plugged into the front o2 sensors (rear o2 sensors had been tuned out). I found the front o2 harnesses jammed up in the engine bay. I plugged the front o2 harnesses into the front o2 sensors like they should have been. Reset the SES, and it has not come back on since. I was expecting to see an increase in gas mileage... but it has actually dropped to about 13.5 mpg highway (was getting 16.5). I've filled up the tank several times since and it's never been above 13.5 mpg of highway driving. I've never heard of working o2 sensors decreasing the mpg compared to non-functioning o2 sensors. The car has a large cam and is running rich because it is untuned, but it should be able to get at least 20mpg highway. Any ideas?
12-14-2010, 01:18 PM
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1. The o2 sensors are still in working condition as far as I know. There hasn't been any codes thrown for them in 300+ miles since I've plugged them in correctly. Is it possible they are not working correctly even if they aren't throwing codes?
2. I'm not expecting good mileage, but 13.5 highway is pretty low even for an untuned modified engine. It does have a mail-order tune, just not a full dyno tune. But I'm just confused as to how I was getting better mpg with the o2 sensors not functioning. Now that they are functioning, the mpg dropped.
2. I'm not expecting good mileage, but 13.5 highway is pretty low even for an untuned modified engine. It does have a mail-order tune, just not a full dyno tune. But I'm just confused as to how I was getting better mpg with the o2 sensors not functioning. Now that they are functioning, the mpg dropped.
12-16-2010, 05:37 PM
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^ IIRC, O2 sensors are basically batteries. They start sending a signal when they reach ~700*. The power feeding them is a heater element so they "warm up" quicker.
12-24-2019, 05:21 PM
#5
Unless you have the knowledge and ability to diagnose/fix this problem you are going to have to spend some money to pay someone to fix it, or months or research learning how to.
The internet can't fix all of your problems. There comes a point when you actually need someone with the skills, knowledge and abilities to fix the issue.
Guys in their mom's basement eating Cheetos can only give so much information. Sorry I offended anyone eating Cheetos in their mom's basement.
The internet can't fix all of your problems. There comes a point when you actually need someone with the skills, knowledge and abilities to fix the issue.
Guys in their mom's basement eating Cheetos can only give so much information. Sorry I offended anyone eating Cheetos in their mom's basement.
12-24-2019, 08:15 PM
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Yeah it does suck doing a search only to find another dead thread with no solutions or closure from the OP.
