Replacing O2's due to bad MPG's
10-25-2013, 11:59 AM
#1
Replacing O2's due to bad MPG's So lately i have been getting around 150 miles per tank. Now i do live in WA and it is cold here so i have to warm my car up for 5 min before i go to work, and work is only 15min away. With that in mind, my O2's are also original, with almost 100k on the clock and being 14 years old, i believe these to be the culprit.
I plugged in my OBDII scanner and got readings of
0.060v-0.900v Bank 1 sensor 1
0.150v-0.850v Bank 2 sensor 1
the drivers side sensor is much more erratic and tends to stay near the 0.060v but after 3000 rpm there is a % reading next to it which has read up to -50% while band 2 reads -2.5% to -7%. i am not sure what all this means all i know is this seams to be my problem.
map sensor reads 12.5 at idle with idle being 875rpm.
I plugged in my OBDII scanner and got readings of
0.060v-0.900v Bank 1 sensor 1
0.150v-0.850v Bank 2 sensor 1
the drivers side sensor is much more erratic and tends to stay near the 0.060v but after 3000 rpm there is a % reading next to it which has read up to -50% while band 2 reads -2.5% to -7%. i am not sure what all this means all i know is this seams to be my problem.
map sensor reads 12.5 at idle with idle being 875rpm.
Last edited by trans_am7935; 10-26-2013 at 08:22 PM.
10-25-2013, 04:12 PM
#4
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I disagree with the concept of applying a specific fixed age or mileage at which these sensors "go bad". I still have the original O2 sensors on my 105k mile '02 car, and still get 16-18mpg (A4) driving around a crowded city in heavy traffic - same as when this car was new. Would new sensors be somewhat more accurate? Perhaps, probably. But likely not enough to make much difference, since my MPG is already about the same as it was when new.
The O2s are reporting a value, and if they are bad then the value will be incorrect and cause driveability/MPG issues. However, if the value is correct then there might be another issue causing poor MPG and the need for extra fuel to be applied to one or both banks.
I don't know what sort of scanner you have, but I'd want to see LTFTs for both banks, also any misfires. That "-50%" sounds like a STFT (short term fuel trim) number.
Anything from a vacuum leak to poor injector spray pattern could be causing poor MPG. You could replace the O2 sensors, but if they are reporting correctly then this won't do anything to solve the actual problem. You've already ordered them so I guess we'll see if this fixes the problem or not.
The O2s are reporting a value, and if they are bad then the value will be incorrect and cause driveability/MPG issues. However, if the value is correct then there might be another issue causing poor MPG and the need for extra fuel to be applied to one or both banks.
I don't know what sort of scanner you have, but I'd want to see LTFTs for both banks, also any misfires. That "-50%" sounds like a STFT (short term fuel trim) number.
Anything from a vacuum leak to poor injector spray pattern could be causing poor MPG. You could replace the O2 sensors, but if they are reporting correctly then this won't do anything to solve the actual problem. You've already ordered them so I guess we'll see if this fixes the problem or not.
10-26-2013, 08:26 PM
#7
ok so i changed my fuel filter and upon inspecting the old one the filter inside was all folded up/collapsed so that was a wise choice, should do that more often. also pulled my spark plugs (all but number 7 cylinder) and they all had a black ring on the base thread, grayish ground strap and the porcelain was still white. now my number 2 plug on the drivers side (number 4 cylinder) was a little wet with oil, so i am assuming that my intake rocker bolt needs to be re-sealed.
I just drove the car (with the old O2's and old fuel filter on) for about 100 miles on the highway and got just under 20mpg. that is not super terrible but i believe there is more to be had considering my plugs tell a rich reading. i was on cruise control at 67mph in 6th gear for most of the drive.
New Fuel Filter and O2's are in, so i will start it up tomorrow and drive around town for 30 min or so for a baseline. anything over 11mpg is good, hoping for 15 or higher. Now i also had a crack on one of my plug wires, and as i removed them and re-installed them, they no longer click when installed on the spark plug. I have had these plug wires on the car for about 5 years, and they have been removed and installed at least 20 times since then. Maybe it is time for a replacement set. The plugs i run are NGK TR-6
I just drove the car (with the old O2's and old fuel filter on) for about 100 miles on the highway and got just under 20mpg. that is not super terrible but i believe there is more to be had considering my plugs tell a rich reading. i was on cruise control at 67mph in 6th gear for most of the drive.
New Fuel Filter and O2's are in, so i will start it up tomorrow and drive around town for 30 min or so for a baseline. anything over 11mpg is good, hoping for 15 or higher. Now i also had a crack on one of my plug wires, and as i removed them and re-installed them, they no longer click when installed on the spark plug. I have had these plug wires on the car for about 5 years, and they have been removed and installed at least 20 times since then. Maybe it is time for a replacement set. The plugs i run are NGK TR-6
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10-31-2013, 09:02 PM
#9
OMG!!!!... so this is what a smooth car feels like! i can actually use my lower RPM's with no shuttering or bucking now. The smoothness alone was well worth the change to the Denso O2 sensors. I just put them on today, so i will run a few tanks of gas through them and report back if this was my issue or not. Looking at the scanner while driving, it appears they were. The readings are so much clearer and more precise now.