I have a 1991 Cadillac Seville 4.9l with 106,000 miles. The #5 fuel injector stays open and floods the cylinder. I have replaced the injector and also switched injectors. But, no change. Every time I try something, I have to change the oil because all the gas from the injector ends up in the oil pan. Any idea of what needs to be replaced or tried to correct the problem.