General Motors' deteriorating financial situation has caused the company to delay one of the most advanced engines that it has ever designed, a 4.5-liter diesel for light-duty trucks.

"We have to make tough decisions right now," GM Powertrain spokeswoman Susan Garavaglia said.

Truck enthusiasts were eagerly awaiting the engine, which would have started production next fall at GM's plant in Tonawanda, N.Y. The engine has unique cylinder heads that eliminate the intake and exhaust manifolds. Its lightweight block has advanced castings for the crankshaft-bearing journals and oil-circulation system.

GM had planned to install the engine in the Chevrolet Silverado and GMC Sierra pickups. The result would have been a fuel-efficient truck priced for less than the heavy duty diesel-powered trucks available now.

The move comes three weeks before a U.S. auto task force is set to determine whether the automaker deserves an additional $16.6 billion in federal aid. GM, kept afloat by $13.4 billion in U.S. loans received so far, is trying to shed brands, sell assets and curb spending as it battles a worldwide collapse in auto sales after four profitless years.

Selling the rights?

GM has been awarded several patents for the engine design, and early tests have shown the new motor to be as smooth and quiet as a gasoline engine. Development of the engine was far along when the decision was made to put the program on hold.

Rights to the engine may be sold to another company, Garavaglia said.

If GM decides to revive the engine, it would likely take at least a year for it to enter production. Meanwhile, GM will not be out of the diesel truck business. The company will continue to offer the 6.6-liter Duramax engine in heavy-duty pickups and modify it as necessary to meet tougher emissions standards.

GM also has just launched Two Mode hybrid versions of the Silverado and Sierra, which get an EPA rated 21 mpg city and 22 mpg highway. The 4.5-liter diesel would have raised the trucks' fuel economy into the mid to high 20s mpg.

Last month, GM scrapped plans to build an engine plant for the upcoming Chevrolet Volt plug-in hybrid and Cruze small car. Instead, the engines will initially come from a European factory while an existing factory in Flint, Mich., is retooled to make the new engines.

GM Powertrain Group Vice President Tom Stephens recently said that all of GM's future production plans are constantly being re-evaluated.

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