Older GMC Diesels



Hi, I bought a 97’ GMC Sierra TD about a year ago specifically to haul my 31’ Airstream. Once I had the dealer check and correct the codes, it took me from Boston to LA absolutely flawlessly. I’ve been using the newer fuel, for better mileage and operation, changing the oil every 3k and adding either a fuel additive or mystery oil, or auto trans fluid every other tank full. Now a year later, she’s smoking black bad and I dunno why. Added a fresh 22 gals of gas and more trans fluid to make it home and within about 5 min. of that the service engine soon light came on. Can you tell me what, besides bad fuel, can cause a normally very low smoke diesel to blow black. It’s not consistent black. But it’s consistant enough to be very embarrassed and feel like I’m some kind of eco-jerk. Help!!!


I’m not sure why you are adding trans fluid to the fuel or all those additives. I would knock that off some but black smoke is a fuel problem. Either the injector pump is going south, an injector problem, or possibly injector timing. I used to have to replace injector pumps about every 100K at $500 each. Don’t know if they are still using the Stanadyne or not but they were junk. Best take it in to a diesel shop for a look see.