Ms. Fire sounds like every guy's fantasy, but when she shows up unexpectedly, there are no smiling faces. She usually brings a Check Engine light with her as an annoying sidekick. Darrell has been getting visits from Ms. Fire recently and is ready to be rid of her. Here's his situation:

Diagnostic codes state a misfire on #2 cylinder of a 2004 Nissan Sentra with 1.8 liter 4-cyl engine. I have changed the spark plugs and the ignition coil, but the Check Engine light came back on. I checked the code again, and it stated that #2 is misfiring (again). I twisted the gas cap to see if that would help. So my question is, what else could be causing the same problem after changing the parts specified?

Darrel, you were headed in the right direction with your troubleshooting. A visit from Ms. Fire (of course we're talking about an engine "misfire") is no fun. Those coil packs are about $75 each, so hopefully you only replaced the #2 module. This should have fixed the issue. Be sure to reset your check engine light to let it reanalyze the situation. You can remove the negative cable to the battery overnight to do that. There were also a few TSBs (Technical Service Bulletins) issued by the manufacturer for the 2004 Sentra regarding ECU issues, which could also be a cause. Check with the dealer to be sure your car has been updated.

There are lots of things you can do every day to keep your car or truck at maximum efficiency. One of the most important and significant is keeping up with regular maintenance. There's no substitute for a perfectly running engine. There was a lot of thought put into your engine's efficiency, but it's up to you to live the dream. These days, taking the mileage that's thrown at you isn't enough. We want to tweak our mileage to the extreme. You've already triple-checked your tire pressure for optimum MPGs, but are you driving for maximum mileage? Your driving habits can burn a lot of extra fuel, leaving you with an actual gas mileage figure that's less than the manufacturer's reported data! They may have tested the cars with a 90-pound driver and a strong tail wind, but the numbers are real, and if you're not getting them, you need to take a look at your behind-the-wheel behavior.

Nobody has a sharper eye on fuel economy than the dedicated gas-misers at About.com's Hybrids and Alt Fuels site. If you're ready to take your gas sipping to new lows, check out Scott's Thrifty Drive for 10 great ways to improve your gas mileage. Every little bit helps!