Why do I need to block my PAIR, and will it affect my mapping?
The factory PAIR (Pulsed Air Intake Reed) simply injects air into the exhaust track (through a hole in the cylinder head from the exhaust port to the top of the valve cover on each cylinder) to help burn any unburned fuel in the exhaust pipe.
In OEM applications, this occurs before the catalytic converter and creates additional heat to help it operate more effectively and lower emissions. In an aftermarket application, the PAIR must be removed and/or blocked to prevent excessive popping during deceleration (aka Decel pop). There is no power gain to be had from blocking the PAIR alone as all aspects of the pair occur after the exhaust gases have left the engine. Additionally, fuel injection mapping has no effect on pair modifications.
Blocking the PAIR and removing the associated components can add up to a considerable weight reduction. If the PAIR is allowed to operate in conjunction with any aftermarket exhaust system which does not utilize the catalytic converter, it can create excessive exhaust heat which may discolor exhaust pipes and lead to premature heat-related failure (to the exhaust itself and especially to the packing in the baffle). Removing emissions components from any vehicle may render it illegal for street use, check with your state and local authorities.
Note: Removal of the PAIR valve assembly from the harness will result in a Check FI light - the most reliable means to eliminate this light is with an ECU flash. Blocking the PAIR manually (block off plates, PAIR valve cap etc.) will not result in a check FI light if the valve and assembly remain attached to the harness - it's just dead weight.
Additionally, if the mechanical PAIR blocking suggestions above still do not reduce deceleration pop enough for your liking, an ECU flash that allows the factory deceleration fuel cut to be adjusted can substantially reduce the popping.