My wife's Altima GXE (2000) suddenly dropped MPG. We bought this car few months ago with 56,000 miles on it. MPG drop happened after I replaced old dirty air filter (which came with the car) with the new one (bought at Strauss Auto). Air filter change might be just a coincidence. The car used to make 300+ miles per gas tank. Today the tank was half empty after just 90 miles. Is it possible that the new filter passes through too much air and air flow meter instructs computer to inject too much fuel? What else might contribute to such a drastical drop of MPG? Service Engine light is not on, so I have no reason to suspect O2 sensor... Thanks for all advises.
no its not possible for your air filter to be causing this, unless it is completely blocking the air supply going into the engine.
First thing I would check for is a leak in the gas tank or fuel system. Rule this out first, since this is also a HUGE safety issue.
Next, pull your spark plugs out and check if they are excessively worn or have alot of deposits or oil on them.
While you have the plugs out, you could also do a compression test on all cylinders to see if there is a problem anywhere.
Also, an inspection of the exhaust system for damage would be helpful, check to make sure exhaust is freely flowing out of the tailpipe... if the baffles in the muffler collapsed, it could cause issues.
loewent, I did three changes just before I noticed sudden drop in MPG:
Changed air filter (old filter was very dirty, but it was original Nissan. new filter came from Strauss Auto)
Changed oil
Made an anti-theft device (we got this car just few months ago). The device is also a suspect - I will email you details.
Looking for the cause of MPG drop I want to tackle possible contributors one by one to make sure that I find the right one.
I noticed MPG drop last weekend. We do not use this car during the week (using public transportation to go to work), so it will take time before we can make enough miles on this car to see the difference.
Last week 1/2 of the tank was gone after only 90 miles. After that put the old air filter back. This weekend the car made 80 miles (with the old air filter) and fuel gauge dropped 1/4 tank. This is almost twice better than last weekend. I will not make any other changes so far - want to see how many miles the car will go until the fuel tank is empty.
I pulled each spark plug wire today to make sure that all 4 spark plugs are working. I did not inspect spark plugs themselves yet. I also checked oil - it is higher than the max. Can too much oil contribute to MPG? Could you tell where is PCV valve in Altima 2000?
I will post next update next weekend since nothing will happen until then.
The friction of your car must have escalated to the point of coincidence and your memory is confusing you thinking that your oil filter was at fault. No, oil filter cannot affect the MPG, not the Air filter neither. I had the same problem with my Infiniti G20T last year(mine was made by Nissan also), until I took it to see this company:
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To prove if my theory is right, I advice after a long drive (40miles) you should touch your right wheel metal with your hand and feel it, if it's hot or real warm, then it is the internal friction that causes your engine to work too hard. When the engine works so hard you got poor MPG.
They fixed it for me once and for all. I am very happy with my car.
Hello Mike, I am not shure what part you think is over heating? I used a product from a California company called Nanolube by StClaire first on my motorcycle and it raised the RPM by about 150 so I supposed it reduced friction , but I do not understand what you mean by: "you should touch your right wheel metal with your hand and feel it" Any way the site for the anti friction is
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Yan Let me know how you are making out, I am curious about the enigma. Patrick
Mike, I was suspecting Air, not Oil filter. The reason is that I replaced the old Nissan filter with the new aftermarket filter. However, even after I put my old filter back, MPGs still remain twice lower than they were before the drop. I explore other options. Will update with any news.
loewent, Last weekend I filled gas at a different gas station, and MPGs seem to get back to normal. I did not do any change besides changing the air filter to the old one in the middle of the previous tank, which did not have any effect on MPG: half tank for 90 miles before changing air filter back, another half for 90 miles after changing filter back. Since I filled up last weekend the car made 260 miles and fuel guage shows about 1/8 tank left. I expect the tank to last for at least 300 miles (previous tank was gone at 180 miles). I will report the mileage when this tank is gone.
Thank you. Yan.
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some research shows that the fuel gauges in these cars are known to be inaccurate. I find that it is very difficult to fill the tank all the way at certain gas stations too.
loewent, I do not think that fuel guage is to blame. Since MPG went back to normal, the last tank lasted (until low fuel light went on) for 340 miles (as opposed to 180 miles when I screamed for help). I am still puzzled why MPG suddenly dropped from 300+ miles per tank to 180 miles per tank and then suddenly went back to normal. I am reluctant to blame bad gas since I did fill up at the same gas station before. In addition, such a poor gas quality must have resulted in power loss, which I did not notice. I think that temporary MPG drop might have been computer related. If I am not mistaken, computer adjusts ignition timing based on gas quality (octane number) so that there is no detonation. As I mentioned before, I installed anti-theft device just before MPGs dropped. I had to disconnect computer while I was installing anti-theft and that might have reset computer memory, specifically its adjustments to gas properties. Once I filled up the next tank, computer migt have adjusted back and MPGs went from 180 miles per tank back to 340+ miles per tank. I am not a specialist in car electronics. Does my explanation seem realistic?
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