Unlike problems caused by a lack of fuel, filtration and lubrication, early LB7 Duramax motors had issues with injectors that had high fuel flow return rates. This was caused by defects in the manufacturing process and caused rough idle, decreased fuel mileage and performance as well as producing smoke at idle. Luckily, if you own a 2001-03 LB7 Duramax, you might be in luck as the factory issued a recall warranty that covers this issue in all 2001-03 Duramax diesels for 200,000 miles or seven years. Contact your local GM dealership service department for more information.