Okay first off i got a 2002 Nissan Altima 2.5s 4 cylinders and i have no idea what's going on with my mileage but i'm getting only 16 MPG on a daily. The best i have ever gotten out of this car was 18 MPG max. I regularly do all my oil changes and i keep my car in top shape with everything maintenance on time. I did a compression test and cars running great with 185 PSI to each cylinder. I have added a K&N cold air intake system, throttle body booster, exhaust system with a rear cat delete, aftermarket resonator and straight piped down to a muffler. I've also put on performance brake pads and rotors drilled and slotted. Straight pipe racing headers as well. I honestly don't know what's going on if i did all these performance upgrade which should let my car more efficient cause i can tell while i'm driving it runs smooth but my mileage just isn't there. I barely rev up over 3000 RPM only when i need to but besides that i'm driving at 2500 RPM shifting it's also a 4 speed automatic with full city driving. Anybody can help me out here on what i can do to boost my MPG? I want at least 20 or so like it should be running. If there any question on what else I've done let me know because i got more things i have done but not listed yet.

Hello, have you checked the tire pressure? When is the last time a tune up was done? Fuel injection, spark plugs, etc.? Could be something simple that was easily missed, I would just double check to ensure everything is in order. Or maybe it is possible that something you added might be hurting the MPG which somebody should chime in soon if that is the case, hope this helps, Good luck.

I've done the spark plugs already but i haven't looked into the fuel injectors cause i never did have a misfire before but maybe their wearing out. Tire pressure is checked regularly so that's not a problem for me. Tune up was done like 4 months ago i'd say we did the full service of spark plugs, fluid flushing and refill, etc. What else do you know that could be changed that might be an issue by any chance?

*Note* posted by adidas2go in another thread.

Here are the 2 main reasons for faulty under fuel economy. Mass Air Flow Sensor, and o2 sensors in the exhaust system itself. Check these items for wire breaks, rigidity, and connection. If they all look good, then unplug your negative on the battery terminal for 10 min. This will reset the computer back to its original settings and erase and possible computer "hiccup" in the system. If all those fail, take it to Nissan and have them run diagnostic checks.

This info may provide a little more insight, this was a discussion in regards to the 2.5 engine poor MPG. Hope this helps.

I've cleaned the mass air flow sensor and also my air filter many times and also changed my o2 sensor recently as well. Maybe i'll try to remove the negative battery cable again because i also did that recently to reset everything. It seems like I've done everything but no results to show for it.

That's crap for fuel economy. The lowest I got was 23 in my altima. Maybe your sucking to much fuel.not enough back pressure in the manifold. You got a lot of low end power?

yeah tell me about it. Possibly but i did change the whole fuel level sensor assembly includes the fuel pump etc. I don't think i got that much of low end power so i'm not sure. I'll ask my mechanic to check everything for me the next time on fuel economy problems i might be having.