Assuming the exhaust leak is located between the exhaust manifold and catalytic converter, it will need to be repaired before your Toyota 4Runner can pass the smog check. The fault here is twofold, in that it posses a visual "defective" failure and more then likely a high emissions failure as well. Having an exhaust leak such as this will disrupt the engine's air/fuel ratio (as it exits the engine) which is necessary for proper catalytic converter operation. The exhaust leak may also cause improper oxygen sensor readings, compounding the high emissions problem. Without correct oxygen sensor readings, the engine emission computer, can not determine how much fuel to the air/fuel mixture. Incorrect air/fuel ratio (14.7:1 is optimal), will cause force the engine to burn fuel inefficiently.
