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Back To Diesel Products>Tuner chips present dilemma at smog test
10:00 PM PDT on Sunday, May 30, 2010
Special to The Press-Enterprise

Q: Michael Sheridan, a Highland resident, owns a 2003 Dodge Ram diesel pickup. His registration renewal this year required him to have a smog test done on the truck, which surprised him.

The pickup has a tuner chip installed in it. He had the chip put in the truck shortly after he bought it, because he'd heard it would improve its fuel mileage, and it did. "My mileage jumped as much as 5 mpg depending on how I drive," Sheridan said in an email. The chip can significantly improve his truck's horsepower at certain settings, too, he said. But when it was time for the smog test, Sheridan learned the chip can actually be a liability.

"Since the chip improved my mpg, then why have I been told by everybody to hide all evidence of it or I would be automatically failed?," Sheridan asked.

Before his smog test, Sheridan removed everything related to the chip from his dashboard the gizmo is installed inside it and the truck passed the test. But he doesn't understand the logic here.

"I would think that when you (improve the mpg on a vehicle, you cut the pollution it puts out and they would actually give tax credits to have them installed, not penalize you," he said. Why are these tuner chips a no-no when it comes to emissions tests?

A: The problem is the assumption that better gas mileage equals cleaner air.

"In most cases it's safe to say he probably is increasing emissions based on that modification," said John Swanton. Swanton is an air pollution specialist with the Air Resources Board, which works with auto manufacturers to get them to meet California's emissions standards. "The lack of proof (that) the device does not increase emissions is what makes it illegal," he said.

There are aftermarket electronic chips you can add to a diesel vehicle that essentially tell the engine to operate differently from how the manufacturer designed it to run, Swanton said. The chip tells the engine to use less fuel under certain conditions, he said. Some chips can improve mileage by even more than 5 mpg, Swanton said.

But when the engine is running "leaner" like this, it also raises combustion temperature, and an engine running hotter tends to produce more emissions, Swanton said.

Because of that, tuner chips or other modifications meant to boost mileage are illegal unless the manufacturer can prove to the Air Resources Board that their use does not increase emissions, Swanton said.

Owners of any vehicle, diesel- or gasoline-powered, should be aware that by using a tuner chip they risk damaging their engines, Swanton continued, again because the chip tells the engine to operate differently than it was designed to do.

The smog program for diesels is very recent, Swanton added.

A smog test has been required for private diesel vehicles - as opposed to commercial trucks such as big rigs - only since Jan. 1, he said.

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