Is Fuel-Saving Device Too Good To Be True?

Dear Car Talk:

I've been reading about a device called Fuel Save Pro that plugs into my car's OBD II port under the dashboard. It says I can save 15% to 35% on fuel costs by letting this device optimize my car's fuel settings dynamically while driving. The cost of the device is under $100, so that sounds like a good deal -- unless it's not.

What do you think? What does the device really do? I called my car dealer and talked to the service department, and they had never heard of it. -- Don

Neither have I. I did buy a Hair Save Pro once from the same company, though. It was supposed to regrow 15% to 35% of my hair, and I'm still bald.

The manufacturers optimize your engine for the best balance of performance, fuel economy, and emissions. And they spend millions of dollars a year trying to squeeze a percent or two more fuel economy out of their vehicles. So, if there were a way to increase fuel economy by 15% to 35% for $99, trust me, it would already come with your car.

I've never heard of this particular device, but most of them do two things. First, they remap the engine and transmission parameters that the automakers have gone through great trouble to set. And if they boost one variable, like fuel economy, it will undoubtedly come at the expense of one or more of the others. So, the downside is that you might damage your engine or transmission, void your warranty, ruin your catalytic converter, give your neighbors' kids asthma, and/or fail your next emissions test.

The second thing they probably do, in my opinion, is exaggerate the results. So, you might not get anywhere near what they promise -- even with all that downside.

Generally speaking, Don, when something sounds too good to be true, it is. And this sure fits that description.

My advice would be to forget about this thing, drive gently, avoid jackrabbit starts, quit warming up your car, and make better use of that $99 by applying it to your gas bill.

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