201526 - Call 05

Kristina bought this truck in California and drove it across country. When she shifts down from 4th to 3rd, the truck backfires loudly. Her mechanic saw the truck had a small exhaust, likely for the California smog test, so he put bigger pipes and a muffler on, but it still backfires. Ray thinks this truck has an anti-backfire valve, which may not be working. Or, the previous owner’s retrofitting to pass the test may have caused the problem.