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When I start my truck in the morning, a black carbon like substance comes out my exhaust, and it smells really rich, what is the cause of that?

Answers from the Automotive Experts

Colleen McGee, Driving Instructor at Americas Driving School Hi David! It could be a bad O2 sensor or a bad catalytic converter.

Jo An Holt, Automotive Journalist at Holt & Associates Fuel mixture seems overly rich. You may have injectors that are leaking down overnight into the combustion chamber. It needs to be diagnosed by a qualified technician to be sure. Do not think that adding injector cleaner will help.

Stephanie Gutierrez, Marketing Communications Coordinator at Victory Auto Service & Glass David, there could be a few different causes. But the rich smell is from your fuel running too lean, causing excessive burn off of fuel in the exhaust. Vacuum leaks, emissions and the fuel supply system could all be possibilities. My best recommendation would be to have an ASE certified technician properly diagnose the problem to avoid the costly expense of trial and error with replacing parts.

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