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Falling mileage w/ new oxygen sensor.

S

spenc938

New member
A couple of weeks ago, I changed the o2 sensor and pcv valve on my car. (98 grand prix se, 3.8l n/a, 191,000 miles) Before this, I was getting about 19.5 miles to the gallon. I filled up yesterday, and I am getting 16.5 miles to the gallon. I reset my trip odometer every time I buy gas, and by comparing that to my fuel gauge, it looks like my mileage is falling even further. I made sure that it was screwed in all the way, and that the plug was seated correctly, and everything looks fine. I was going to put the old sensor back in to see if that fixes it, but I went and checked the garage where I left it, and someone threw the old sensor away. Any help?
 
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Not that I think its solely responsible, but I've had bad things come from using non-ACDelco PCV valves. Burning oil, mileage issues, etc. Did you use an ACDelco PCV valve? The kicker is that they're usually cheaper than the ones at Autozone. :th_laugh-lol2:
 
How many miles hav eyou put on the new sensor?
PCMs have a learning curve. New sensors somtimes take a bit for the computer to learn how they read(faster,slower, o2 ranges that were not being read before because of a bad sensor). That is somtimes the problem with other modifications as well, like new PCM files and aftermarket exhaust and valvetrain parts
Somtimes tho its not any of the above and you got a bad sensor right out of the box
we have had this happen a few times, we played with differnt brands until we found one that works.

also did you touch the sensor before putting it on? Oils on your hands or other greases can foul out a sensor in no time flat
 
I used a pcv valve from autozone. I honestly have no idea what brand it was. When I look on their website, they only show one, so I would assume it was this one.

AutoZone.com | Shopping | Parts | Product Detail - PCV Valve

I have put about 200 miles on the new sensor.
This was the first one I have ever replaced and I didn't know how sensitive they were, so I only held it by the wires. It was kind of a pain in the ass, but I guess I was correct in doing it.

By the way, I bought the sensor from ebay. I have heard that there is a way to check the voltage on them to see if they are functioning correctly, and if anyone is willing to explain, I could try that.
 


Ok. I'll call around tomorrow and try that first. Even if that fixes the problem, I am still looking for other ways to increase gas mileage. Since I bought it in september I have done: air filter, fuel filter, spark plugs, wireset, oxygen sensor, and the pcv valve. I saw the how to on this site about the 4 inch FWI and was wondering what something like that would do to my mileage. I don't want to buy a k&n or wizaired because the car has a salvage title and is only worth about a thousand bucks, but I wouldn't mind spending up to 60-70 on a homemade ghetto intake, as long as it won't hurt gas mileage.
 
change your driving habits, let the car coast when stopping, accelerate like there is an egg under the pedal, judging by your mileage you have a heavy foot 9I am averaging almost 23 mpg in the gtp and drive 99% city)
 
I really do try to drive slow, but I don't have the patience. Plus, since I haven't been working each trip I take is exactly 1.8 miles. I basically only go to school. I am getting better, but I still would like to look at other things to help mileage. The FW intake in particular.
 
those short trips are killing the car, it needs to be driven and warmed up, take a good 10 mile minimum trip ( that is what we had to do at the dealer after any repair)
 


Well, when I go to the dealership to pick up a new PCV valve, that'll be 6-7 miles each way.

But even before when I was getting about 19, it was still just short trips.
 
The car does get fully heated in the afternoons. With 800 cars leaving the high school at the same time, it takes me some time to get home. I know that short trips aren't particularly good for it, but why do I need such a long distance? How often do I need to do this?
 
A FWI won't help your mileage. It may hurt it because of the cooler air coming in (cooler air means more fuel is used which means more power). If you want good MPG, a hot air intake is great for it. I ran one for about six months and saw the best MPG I ever had with this car.
 
spenc938 said:
The car does get fully heated in the afternoons. With 800 cars leaving the high school at the same time, it takes me some time to get home. I know that short trips aren't particularly good for it, but why do I need such a long distance? How often do I need to do this?
Click to expand...

the computer doesn't go into a learning mode until at 45 mph (from research I have done) it then uses the distance to change values, and compare sensors
 


So a warm air intake would be taking out the box and sticking a cone filter on the end of the accordion tube? And this should improve mileage? How much would this hurt performance?
 
Holy freakin crap. Since I last filled up, I had driven about 40 miles. Ten of this with the autozone pcv valve, ten around town with the ACdelco PCV valve, and 20 on the freeway driving very agressively. I topped of the tank, did the math, and was getting on average 23.57MPG. I sure do hope this will continue.

On another note, the guy at the dealership was a complete jerk. He was extremely condescending, and basically told me I was an idiot to listen to someone off of the internet. He went on to say that it is not possible for the valve to effect mileage, and even tried explaining to me where it was located, even though I had just replaced one. Some people....

Edit: I am still interested in either a warm or a cold air intake. If someone with first hand experience could give me some rough numbers on the effects of each as far as performance and mileage, it would be greatly appreciated.
 
I am back down to 16 again. I was getting 19 just a few weeks ago. It is not the PCV valve, and I can't afford to buy a new o2 sensor, just to test it. ANY SUGGESTIONS?
 
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