Oxygen sensor questions - GS400
09-11-08, 09:50 AM
#1
Oxygen sensor questions - GS400
It is a 2000 and just turned 103K miles with the original oxygen sensors. Eventhough I have a high stall torque converter and upped the rear gearing from 3.23 to 3.76 I am getting horrendous gas mileage; like 14.5 driving like a grandma. 
Can oxygen sensors lose efficiency over time or do they just work and then suddenly not work? If they do "wear out" over time will it throw a CEL or not necessarily?
I read that my car has 3 of these O2 sensors and I was thinking of replacing all of them...I think they can be had for $50/each on Ebay. Does anyone have any experience with this or changing them? Please help guys...
Can oxygen sensors lose efficiency over time or do they just work and then suddenly not work? If they do "wear out" over time will it throw a CEL or not necessarily?
I read that my car has 3 of these O2 sensors and I was thinking of replacing all of them...I think they can be had for $50/each on Ebay. Does anyone have any experience with this or changing them? Please help guys...
09-12-08, 07:04 AM
#3
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i haven't changed them on a gs, but 02 sensors efficiency can vary. changing your torque converter and the gearing is definitely not going to help. the gearing makes you turn more rpms at the same speed and the torque con. makes you rev higher to even start moving. i would expect gas mileage to go down, but not sure how much.
09-12-08, 10:44 AM
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Have a shop put a sniffer on the exhaust. If an 02 sensor goes I would think your car will go rich on the injector cycle which will show on a emmissions test. I've got to believe this would also throw a CEL as this might equate to a "limp home" mode. While it's kind of a pain, pull a plug and take a look for buildup caused by a rich fuel cycle. 02's are there to keep the a/f ratio correct for optimal performance and low emmissions.
09-12-08, 10:47 AM
#6
I know the mods I have effect mpg by approx. 2mpg as per research on CL. So if I am at 14-15 mpg does that mean 16-17mpg is normal for a GS400 when driven lightly to moderate? I cleaned the TB, I have silky smooth Amsoil in the trans and silky smooth Royal purple in the rear diff, a brand new filter from Amsoil. The ONLY thing that comes to mind first is either my 2.5 year old torque master spark plugs and the O2 sensors.
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09-12-08, 11:26 AM
#8
...then I guess I'm not too far off of where I should be. The thing is I have read on MANY gas mileage threads of people with GS400's and GS430's getting 320 - 380 miles on a single tank of gas! I am DAMN LUCKY if I get 250 miles out of a tank. There is definately a lot of traffic here on long island but this is just ridiculous. I literally drive 40 minutes everyday (20 minutes each way to work 5 days a week) and probably no more than 40 minutes each day on Saturday and Sunday and I can't even make it to a full week (7 days) on a tank! I usually fill up every 5-6 days @ $70. I feel like I barely drive (no leisure driving anymore) and the car EATS gas like no other.
09-12-08, 11:40 AM
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I'm one of those who does get between 320-380 miles to a fillup (usually less than 17 gallons). I have no real mods on the car other than 20" tire/wheel combo but I drive roughly 75% hwy which leverages my per tank averages to the rated hwy mileage side of the equation.
I must also admit that these higher readings are do in no small part to a shift in driving habits. The NAV in my car shows the instant mpg readings and I use this to maximize my fuel economy without seriously impacting my driving enjoyment.
You might want to invest in a product called a Scan Guage, which can show you all the operational parameters, readings and aspects of your engine in real-time. This type of tool is used everywhere from maximizing economy to maximizing performance and efficiency.
I must also admit that these higher readings are do in no small part to a shift in driving habits. The NAV in my car shows the instant mpg readings and I use this to maximize my fuel economy without seriously impacting my driving enjoyment.
You might want to invest in a product called a Scan Guage, which can show you all the operational parameters, readings and aspects of your engine in real-time. This type of tool is used everywhere from maximizing economy to maximizing performance and efficiency.
09-12-08, 01:40 PM
#12
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09-12-08, 01:56 PM
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I think you are on track with 14mpg for your mods. I get between 13-16 with my gs430 and it is all stock. LA traffic takes it toll on my milage as well. The only time I get 16 and above is when I mix in some freeway driving...that is if the freeway is moving ha. In order to get over 15mpg I feel I have to drive a like an old man.
