Rattling/clattering from PAIR valve...

'06 S'Wing 16.5k miles:

For the last few months I have been hearing a subdued and seemingly getting louder, somewhat annoying rattling/clattering apparently emanating from the right side of the engine's upper end; and it occurred to me I had read in the Burgman forums of B400 owners having similar experiences and tracing it to the PAIR valve. I never had that situation as it was one of the first things I disabled on my '03 B400.

So after studying the FSM for a while it seemed that the value could be disabled by simply unplugging its electrical connector, and that said connector might be accessible through the "maintenance" cover over the spark plugs--sure enough it is, and unplugging it made the noise go away.



The PAIR system is not monitored by the ECU, and simply disconnecting the valve leaves it in the same state as when it is not activated by the ECU. On my Burgman 400 I took time to fabricate a block-off plate for the PAIR check valve port in the head so that I could remove the valve and associated plumbing, but that was not really needed;

I may make one for the S'Wing if I get ambitious...

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Edit:

Disabling this will of course affect emissions, if you live in a place that "sniffs" bikes this would mess thing up (do they do that on bikes in some places? I've been if Florida for 26 years now and they do not even sniff cars here)

Great info, Cliff. Thank you.

So in disabling the PAIR valve wouldn't that allow more 'raw' fuel to enter the exhaust system and cause loud(er) backfiring?

My '09 S/Wing has the O2 sensor in the exhaust; I hear a soft popping in the exhaust when the PAIR valve functions on deceleration. I have also noticed that the muffler 'appears' to be significantly hotter after a long, sustained, high speed ride. Neither of these were evident on my, non-O2 sensored, '03 S/Wing so I've attributed this popping noise (along with increased fuel economy) to the ECU / O2 sensor causing the engine to run leaner and the PAIR valve to increase the exhaust temps in the muffler.

With a less restrictive aftermarket exhaust and the PAIR valve disabled wouldn't that cause some pretty significant backfiring, if not actual flames at the exhaust? Or would the O2 / ECU "read" the changed exhaust and further lean out the air/fuel mixture to reduce that backfiring? And if that is the case then wouldn't that also lead to burnt exhaust vavles and/or holed pistons?

Tim

I believe PAIR valve adds air into exhaust through a passage in the head somewhere. BUT not into combustion chamber. Added 02 helps burn hydrocarbons in exhaust system, this will make more heat for sure. Less pollution.
Back fire is usually caused be a lean A/F ratio not rich.
Narrow band 0/2 is always switching lean-rich back and forth. This tends to keep blend fuel trim in the middle. 14.7 is leanest ratio for best economy---12.5 for best power.

Disabling PAIR might lean it out some but 02 should be able to adjust.

As stated in Mech 1 twa's  post, The PAIR system reduces emissions by providing a path for filtered air from the air box to be sucked into the exhaust port by the lower than ambient pressure at the trailing end of the exhaust gas pulse (after the exhaust valve closes). This fresh air mixes with the hot exhaust gasses; and at that any unburned hydrocarbons in the exhaust are burned--this does of course create heat and cause the exhaust valve, exhaust port and head pipe to run hotter than they would otherwise.

It is often called a "pulsed air injection" or similar, however that is a misnomer as it does not "inject" air; it just provides a path for the low pressure tail of the exhaust pulse to pull in air. The full path on most systems is as shown below.

This is the Suzuki Burgman 400 system. Suzi's service manuals are better than Honda's, with a lot more detail, and a lot of "why"and "how" information. The arrows and annotations are mine, the PAIR info is in green, red is the PCV flow.



You can see that (when the PAIR valve is open) filtered air from the airbox can flow through the solenoid valve and as far as the PAIR reed valve. Then when the exhaust pressure falls below ambient air is drawn into the exhaust port. Disabling the PAIR system causes the exhaust valve, exhaust port, and head pipe to run cooler.

The Silver Wing system works the same, and is actually physically very similar.

The ECU controls the opening of the PAIR solenoid valve as it sees fit using a combination of data such as ECT, IAT, throttle position, manifold pressure and engine speed. Typically it is open at idle and closed or near closed throttle deceleration.

Disabling the PAIR system was, on the '03 to '06 400 Burgmans, a common "fix" to prevent exhaust popping and full blown backfiring on deceleration.

With the '07+ S'Wing disabling the PAIR could cause the O2 sensor to believe the mix is richer than intended. I am not intimate with the later model;s EFI system however if like many this would only be an issue at idle where closed loop operation might lean the mix if the PAIR is disabled. On closed or even partially closed throttle deceleration it would be quite odd (in my experience) for an EFI system to attempt to closely control AFR using O2 sensor feedback.

It would be simple enough to unplug the valve connector and ride a while with a "weather eye", monitoring for ill-effects...

o2 plays a small part in overall fuel mixture. MAP manifold absolute pressure sensor plays a much bigger role in fuel delivery.

Honda uses their system called PGMFI Programed fuel injection. Its been around since 80's.
If a sensor fails system can run a base kind of program to keep you going.Sensor value will default to a set reading.. If MAP fails you will have a very rough running engine. The check engine will be on if anything is reading out of spec. or fails.

Mech 1 twa wrote:

o2 plays a small part in overall fuel mixture. MAP manifold absolute pressure sensor plays a much bigger role in fuel delivery.

Honda uses their system called PGMFI  Programed fuel injection. Its been around since 80's.
If a sensor fails system can run a base kind of program to keep you going.Sensor value will default to a set reading.. If MAP fails you will have a very rough running engine. The check engine will be on if anything is reading out of spec. or fails.

Yes, most all EFI systems have fail safe modes, that fall back to preset values--Ford calls it FMM, Failure Management Mode.

The Burgman 400 FSM provides a table showing the "fail safe" assumptions for each critical sensor: