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Discussion Starter · #1 · (Edited)
This tutorial will show you how to safely disable the Secondary Air Intake System on a 2015 Ducati Scrambler.

Before we begin, some explanation of this system is probably in order...

The Secondary Air Intake System (also sometimes referred to as a “PAIR” - Pulsed Air Intake System) is used to decrease the amount of unburned fuel that may be present in a exhaust system, post combustion. There are two primary reasons for manufacturers to implement a system such as this.

This first is to simply “clean up emissions”. The second is to prolong the useful life of the catalytic converter.

A catalytic converter is a device that uses a catalyst to convert three harmful compounds in car exhaust into harmless compounds.

The three harmful compounds are:
  • Hydrocarbons (in the form of unburned gasoline)
  • Carbon monoxide (formed by the combustion of gasoline)
  • Nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen)
Carbon monoxide is a poison for any air-breathing animal. Nitrogen oxides lead to smog and acid rain, and hydrocarbons produce smog.

In a catalytic converter, the catalyst (in the form of platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in a muffler-like package attached to the exhaust pipe. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.

The lifespan of this unit is in direct proportion to the amount of unburned fuel it needs to neutralize - this is why manufacturers incorporate a Secondary Air Intake System. Reducing the amount of raw fuel in the system will prolong it’s effective life.

The SAI injects pulses of air into the exhaust manifold, burning off the majority of any unburned fuel, reducing the amount of work that the catalytic converter would have to do.

The way it works is that the ECU sends a signal to a solenoid valve, which opens and sends clean air from the air intake to the exhaust system - under conditions where incomplete combustion would normally occur.

If you have modified the exhaust on your motorcycle, removing the catalytic converter, than this system causes noticeable “popping or gurgling” in the exhaust, especially noticeable while reducing RPM’s. This causes no immediate (or long term) damage, but most - including myself - do not care for this gurgling “ruining” the rumble of our new aftermarket pipe.

Please do not confuse this phenomena with the noise caused by fitting a freer flowing exhaust and NOT altering the fueling to match! Doing so causes the same thing (detonation in the exhaust system), but on a larger scale due to the system being overly lean - which can cause MANY other issues.

Enough with the “technical details” already, here is how you do it...

This is a VERY easy operation and you will need the following supplies:

  • Shrink wrap tubing
  • 2mm hex key
  • Miniature standard screwdriver
  • 2 - 1/4″ spade connectors (male)
  • Soldering iron & solder
  • Sugru (this is optional, but very useful stuff - more on this later)
  • A 47ohm - 1/2watt resistor - NOT SHOWN (tolerance does NOT matter in this application)
  • Some 18ga insulated wire - NOT SHOWN
Using the 2mm hex key, remove the right side cover (located just beneath the fuel tank). This is what you will see behind it..

The green arrow shows the solenoid valve that opens, pulsing air into the exhaust. The red arrow is the connection from the ECU. Remove this connection by pressing down on the tab that is directly at the red arrows “point”, and pull the connector off.

Here is a view of the inside of the connector...

Look closely at this picture, there is a small plastic “tab” (shown directly at the arrows point). Using the miniature screwdriver, gentry pry this up (towards my index finger) while pulling the wire out from the rear of the connector. Repeat this process with the second wire. You will have two wires, each with a “female” connection, and a now empty plug.

Now to the part about “Sugru”...

Surgru is a self-setting silicone rubber. It feels like play-dough, and it's that easy to use too. It bonds to almost any other material and cures just by exposing it to air. It forms a semi-permanent, waterproof seal on ANY material, but can be easily removed later. It is effective in temperatures ranging from -50°C (-58°F) to +180°C (356°F). Totally useful stuff, I use it EVERYWHERE.

Here is a LINK for more info on this awesome stuff.

Take some Sugru and stuff it into the back of the now empty connector - then plug it back into where you disconnected it from.

If you just leave this disconnected, then the bike will throw an error code (check engine light will come on), so we have to rectify that. To do so, we will be “bridging” the connection with a 47ohm, 1/2watt resistor (tolerance does NOT matter in this application). This will “fool” the ECU into thinking that the SAI solenoid is still connected and fully functional.

Here’s how to fabricate this simple bypass. Take the 1/4″ spade connectors (2)...

And grind (cut, file, whatever) until they fit the now exposed female connectors snugly. It will look something like this...

Cut a couple of pieces of 18ga wire to approximately 2 inches in length, tin the ends, then solder each to the resistor. It should look like this...

Now, attach the spade connector which we modified earlier to each exposed end, and cover everything with several layers of shrink wrap tubing.

Now, plug each end into the female connectors coming from the ECU, and cover everything with more shrink wrap.

The resistor will get hot when it receives current from the ECU (this is what resistors do!), so let’s be careful to insulate well. Take another “blob” of Sugru, and fashion a “ball” covering the resistor.

The resistor only heats up when current is applied, this is infrequent and for short durations.

I elected to locate and wire tie this “bypass” as shown in the photo below. I wanted to keep it out of behind the plastic side cover, exposing it to cooling air.

Here is how it looks when the side cover is installed once again...

Simple, and totally reversible. The “popping” is now greatly reduced (almost eliminated entirely), and the bike runs as it should.

Originally posted on my personal blog - moto-graphic.com
 
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Discussion Starter · #3 ·
Is it not possible to use Rexxer to turn off the SAI?
You cannot turn the SAI off with the Rexxer, but it can prevent the error code from being thrown when it is simply unplugged. This is how I do it - because I own a Rexxer unit - simply unplug it and suppress the error code.

My post was for those who do not own one, and need to disable the SAI.
 

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Discussion Starter · #4 ·
Update...

Just discovered that if you disable the O2 sensors (via Rexxer or some other means, you a can leave the SAI completely intact. The solenoid valve will not operate without feedback from the lambdas, and remains closed.


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Discussion Starter · #6 ·

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Interesting thread. Can the air injection parts be removed? Or are they integrated with other parts that can't be disassembled?
I haven't looked at mine yet...
 

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I would use a 5 or 10 watt power resistor. I tried 2 0.5 watt 100 ohm ones in parallel (so 1 watt 50 ohm total) just as a sanity check because I had them on hand. While the ECU was happy, they got quite hot. Now that was with the ignition on but engine not running which is not usual but still a possibility. If my mathematics are correct the system would be using about 3 watts when active. I intend to try a 5 watt - should cope easily. Also I'd like to try plugging the resistor assembly into the socket from the ECU directly and sealing it rather than removing the wires from the socket. I reckon that's easier to put back to stock. Obviously both plug and socket need to be sealed up.
Blocking the input or output hoses sounds good too but it's pretty fiddly in there.

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Ok tried it. While the apparatus didn't throw an ECU error or catch fire, it did absolutely nothing to the bikes running.
I have a hunch that the full Termi map disables it anyway - come to think of it, it's never popped badly on deceleration....I was more interesting to see if it fixed the floating idle. It didn't.
I put the SAI plug back in.

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Did anyone else try again to put the resistor to trick the ECU? Were you successfull to avoid the popping in the exhaust?

I did a test on my Monster 797 (same 800cc engine as the Scrambler), I put a 1kOhm resistor to reduce the electrical current (and the heat).
I realized that:

1) Just by doing Ignition ON (Key ON), the voltage difference on the resistor poles is 0V, due to the fact that V=R*I, V=0 means that no current flows inside (i.e. the ECU does not turn ON the valve). in this condition, engine malfunction lamp (MIL lamp) is OFF.

2) Cranking the engine (engine cold condition), the ECU still does not turn ON the valve (0V on R pins, so I=0). MIL lamp is still OFF.

3) After riding few km (~2 km), the engine failure lamp (MIL lamp) suddenly turned ON, and the idle engine speed became very rough. I suddenly stopped the bike on the side of the road, then remove the resistor, reconnect the wiring harness male connector to the valve female connector. Started the engine again, no issue anymore, but the MIL stays ON (I guess it takes few driving cycles to turn it OFF definitely)

4) I read the DTCs using an ELM327, and DTC P0413 was "Confirmed DTC". The meaning of this DTC is "Secondary Air Injection System Switching Valve A - Circuit Open".

My conclusion is that the resistor value of 1kOhm is too high, and therefore the first time when the ECU turns ON the valve (transistor closes the circuit to GND and therefore the current flows in the resistor), the voltage detected by the ECU feedback diagnosis is not in the right range, so the ECU detects "Open Circuit".
The reason why this happened after some kilometers, I think it's due to the fact that the engine had to heat up (maybe lambda sensor too) before the valve control is activated.
Definitely, a smaller resistor has to be used: some people were successful with a 50 Ohm, while I got an error with 1000 Ohm, so I think that there's somehow a "max R tolerated" limit. I will try with 50 Ohm resistor too, however I am concerned by the heating, so I bought "10 W resistors" on Amazon.

By the way, someone in another forum said that putting the resistor is worthless, because anyway this valve is "normally Open" and therefore if not powered, the valve stays open and intake constantly communicates with the exhaust (except for the reed valve in series, which stops back flow) and this could have bad influence to lambda control. So, the resistor does not solve the popping issue. Is this true or not? Did you solve the popping issue just by adding the resistor? Did you notice any side effect on idling?
 
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