A few months back the family and I went on a trip to Virginia City and I noticed that once I got above 2,000 ft elevation my 1993 smoked out the exhaust, no biggie but my question is every once in a while it puffed way darker, pure black smoke. Could that be and injector starting to stick open? And then today I took my son and a couple other students from his class to san fransisco for a field trip and because the elevation wasn't high I didn't smoke but I did blow a few puffs while pulling a grade, but not as dark as up in the hills.