Another problem common with Jeep fuel injectors is leaking O-rings. Each injector has two O-rings that keep pressurized fuel in. The upper O-ring can crack and leak fuel, which is quite noticeable when the engine is running. If the lower O-ring shown here becomes compromised, a vacuum leak will form. Depending on the severity of the leak, a misfire will occur as the computer tries to manage the air/fuel mixture.