# 2001 Altima Horrible Gas Mileage



## rbabb1 (Jul 13, 2016)

I bought my 2001 Altima with 95,000 miles on it a few months ago. I got about 400 miles out of the 15.9 gallon tank. Roughly a month ago I started to only get about 150-200 miles out of the tank. I found some new cats off of another altima I'm going to get for 50$. Would that be worth doing? Or is there something else? Anyone else experiencing this?

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## smj999smj (Jan 1, 2006)

Well, selling/purchasing used catalytic converters is illegal unless they have been re-certified, but, overlooking that... It would be a lot easier to do an exhaust back pressure test to see if there is any restriction rather than deal with rusted bolts...and potentially breaking bolts. An exhaust back pressure tester is threaded into the O2 sensor bung in the exhaust and the engine is started and the gauge will show weather there is any restriction or not. If you haven't experienced any change in performance, there's a pretty good chance that there isn't a converter issue. 
I would start with the basics. Check for any stored trouble codes in the ECM. Check the fuel pressure (if the regulator is not working, fuel pressure will be excessive and cause the engine to run rich); I would also do a fuel pressure leakdown test to check for leaking injectors while the test gauge is installed. Check the condition of the secondary ignition system. Check the upstream oxygen sensor operation. Check the operating temperature of the cooling system (if the thermostat is stuck open, the engine will not heat up enough to enter closed loop and this will also cause a rich mixture). Check vacuum hoses for leaks, splits and proper connections.


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## rbabb1 (Jul 13, 2016)

I do have a problem with my thermostat reading cold on the dash, but it doesn't just sit there. The needle wiggles and jumps all the way down when I hit the gas. 

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## smj999smj (Jan 1, 2006)

I would start by replacing the thermostat and see what happens. I highly recommend using a genuine Nissan thermostat, as aftermarket 'stats tend to be a little "off-spec" sometimes.


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