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THE CAR DOCTOR

Trading in will keep you in a rut

Plus: Possible engine sludge, horsepower gains that aren't

By John Paul
Boston.com Columnist / January 27, 2010

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Q. A few years back, my wife and I were forced to trade in our Hummer H3. At that time my wife was driving from the South Shore to Boston for work and with gas over $4.00 a gallon. In this situation, we were spending over $200 a week for both of our vehicles to commute to work. We ended up trading the 2006 H3 in for a 2008 Nissan Rogue SL, figuring if the payments were the same then we would save money on gas. When we made this deal, we had to roll over the negative equity into the new loan. It's been two years, and my wife is still racking up the miles, 48,000 miles in just two years. I am concerned that this will be a vicious cycle when we try to get into another vehicle. Is there anyway, outside of a large down payment, to make up for the negative equity and stop the "bleeding"?

A. The short answer is no. Continuing to trade will continually put you in the same situation that you are in now. To get yourself out of this situation I would try to keep the car for as long as possible, pay the car off, and then continue to pay yourself to build up a reasonable down payment on your next vehicle.

Q. I'm bombarded with offers of fuel regulators and larger capacity injectors promising to increase my engine's performance. But it seems to me to be a waste of money because as soon as the O2 sensor sees a richer mixture, the ECU is going to shorten the injector time to bring the fuel/air ratio back to what it's tuned for anyway! Am I right, or have a missed a simple performance trick here?

A. You are correct, adding more fuel in going to do little to increase performance. If you have the car's computer "re-mapped" the engine will be able to take advantage of the additional fuel and in turn will produce more power. Although tinkering with the car's computer can improve performance, it can have a dramatic effect on fuel economy as well as emission levels.

Q. For the second winter in a row, the malfunction indicator light (MIL) on my 2001 VW Passat has come on when I start my car the first time after a week or so if the engine has not run at all. I park it on the street, so it's been out in the cold for a while. Besides the MIL, I also have a digital message reading "Emissions Workshop." I am not clear what this is specifically referring to. Last year, after a few days of using my car every day, the MIL and the emissions message disappeared. I am hoping the same will happen this time around. Do you have any idea as to what could be malfunctioning, and whether or not it is something that is OK to sit on for a week or so?

A. This problem could be a result of sludge build-up in the engine. Combine sludge and cold weather and this could be the cause of the engine light and workshop message. Have the computer system scanned to determine the code and determine the correct course of repair.

Q. My car sits idle, months at a time. When I go to start it up after about three months, the battery is dead. I know this is probably from the digital clock draining the battery.   Would a device such as the Battery Tender solve this problem? Currently I have had to disconnect the cables from the terminals to keep the battery charged.

A. The Battery Tender and other "float" chargers are designed to maintain a battery that is in good condition. These small chargers have built-in circuitry that maintains the battery without overcharging it. There are many items in today's cars that continually use small amounts of battery current that when left unattended will cause the battery to go completely dead.

John Paul is the public affairs manager for AAA Southern New England. He can be reached at jpaul@aaasne.com or on Twitter @johnfpaul.