#1 Thread starter
PAIR valves are the same on the fifth generation VFR, so it should apply there as well.
PAIR (Pulsed Air Induction Reed) valves are an emissions control device that takes clean air from the airbox and injects it into the exhaust tract of the engine, on the backside of the exhaust valve. The main idea is that when an engine is running rich for whatever reason, particularly when you back off the throttle, the exhaust gas will have unburned fuel and no oxygen. Fuel vapors are nominally worse pollutants than combustion byproducts, so putting fresh air into the exhaust while its still hot will cause the fuel to combust inside the pipes rather than be released into the atmosphere as-is. It also keeps the catalytic converter warm so it works better.
Anyway, the wierd knocking noise you get sometimes when pressure suddenly rises in the airbox compared to the exhaust pressure is caused by these things. Your engine runs slightly more efficiently without it (how much I have no idea), but it also just sounds better.
Here's the stuff you remove in block diagram form:
[image: user posted image]
The blue area highlights the solenoid control valve for the PAIR system. Its attached to the back of the airbox and has three large air hoses and one four-element electrical wire attached to it.
The red crosses indicate where we're removing the hoses from. One is the input to PAIR from the airbox, on the left rear corner of the airbox. Two of them supply air to the PAIR valves themselves on the valve covers.
To get to everything, you'll need to remove the airbox from the velocity stacks as if you were performing a starter valve sync. If you don't know how to do that, follow the Starter Valve sync How-To located here:
http://www.vfrdiscussion.com/forum/index.php?showtopic=7935
After you've lifted the bottom half of the airbox, start the mod by removing the PAIR hoses from the engine and airbox. Don't mistake the aft PAIR hose for the crankcase breather! (Its output is on the right rear corner of the airbox.) Then disconnect the PAIR solenoid control wire, and remove the solenoid and hoses as one piece. The solenoid "hangs" on the airbox and doesn't have any screws holding it in place, so you can just pull it off.
Since we're taking the hoses off, we need to cap the PAIR ports somehow. Several ways to do this...you can machine a cover to replace the one that's there, you can remove the cover and fill the port with JB Weld, or you can put a $2 rubber cap over it. I'm lazy so I picked the latter method. Here's what it looks like on the front side:
[image: user posted image]
I used 5/8 inch rubber bypass caps from NAPA, P/N: 660-1696, and zip tied them around the base to keep them airtight.
Here's what it looks like on the back side:
[image: user posted image]
To plug the airbox outlet, I used a 1/2 inch bypass cap from NAPA, P/N 660-1697, and pushed it in from the outside.
Last step is to put everything back together. Without the PAIR hose running to the front cylinders, its at least a little easier to set the airbox in place! After doing this mod the annoying knocking noise of the reed valves was gone, and the engine was slightly smoother. Of course, that's just an opinion, and I also did a starter valve sync at the same time.
Next step is evap canister removal...
PAIR (Pulsed Air Induction Reed) valves are an emissions control device that takes clean air from the airbox and injects it into the exhaust tract of the engine, on the backside of the exhaust valve. The main idea is that when an engine is running rich for whatever reason, particularly when you back off the throttle, the exhaust gas will have unburned fuel and no oxygen. Fuel vapors are nominally worse pollutants than combustion byproducts, so putting fresh air into the exhaust while its still hot will cause the fuel to combust inside the pipes rather than be released into the atmosphere as-is. It also keeps the catalytic converter warm so it works better.
Anyway, the wierd knocking noise you get sometimes when pressure suddenly rises in the airbox compared to the exhaust pressure is caused by these things. Your engine runs slightly more efficiently without it (how much I have no idea), but it also just sounds better.
Here's the stuff you remove in block diagram form:
[image: user posted image]
The blue area highlights the solenoid control valve for the PAIR system. Its attached to the back of the airbox and has three large air hoses and one four-element electrical wire attached to it.
The red crosses indicate where we're removing the hoses from. One is the input to PAIR from the airbox, on the left rear corner of the airbox. Two of them supply air to the PAIR valves themselves on the valve covers.
To get to everything, you'll need to remove the airbox from the velocity stacks as if you were performing a starter valve sync. If you don't know how to do that, follow the Starter Valve sync How-To located here:
http://www.vfrdiscussion.com/forum/index.php?showtopic=7935
After you've lifted the bottom half of the airbox, start the mod by removing the PAIR hoses from the engine and airbox. Don't mistake the aft PAIR hose for the crankcase breather! (Its output is on the right rear corner of the airbox.) Then disconnect the PAIR solenoid control wire, and remove the solenoid and hoses as one piece. The solenoid "hangs" on the airbox and doesn't have any screws holding it in place, so you can just pull it off.
Since we're taking the hoses off, we need to cap the PAIR ports somehow. Several ways to do this...you can machine a cover to replace the one that's there, you can remove the cover and fill the port with JB Weld, or you can put a $2 rubber cap over it. I'm lazy so I picked the latter method. Here's what it looks like on the front side:
[image: user posted image]
I used 5/8 inch rubber bypass caps from NAPA, P/N: 660-1696, and zip tied them around the base to keep them airtight.
Here's what it looks like on the back side:
[image: user posted image]
To plug the airbox outlet, I used a 1/2 inch bypass cap from NAPA, P/N 660-1697, and pushed it in from the outside.
Last step is to put everything back together. Without the PAIR hose running to the front cylinders, its at least a little easier to set the airbox in place! After doing this mod the annoying knocking noise of the reed valves was gone, and the engine was slightly smoother. Of course, that's just an opinion, and I also did a starter valve sync at the same time.
Next step is evap canister removal...