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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.
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Old 06-18-2009, 09:03 AM   #1 (permalink)
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Air Injection be gone DIY 2009 EFI Bonny/Thrux

As the mystery of the new EFI bikes become unraveled and performance opportunities explored, few subjects of discussion are as debated if not misunderstood as air Injection as it relates to electronic fuel injection (EFI). The carb boys have a lot of experience with removing it on their bikes and know that it has no affect on A/F ratio. Some believe removing AI upsets the temperature of the O2 sensors on EFI. It doesn’t. EFI changes things but not as much as some believe. AI and EFI are almost independent entities made to work together but not dependent on each other. EFI doesn’t want or need AI to operate effectively.
AI in fact needlessly complicates things and hence for a hotrodder, many of us being card carrying members, AI simply must go and what this thread is about.

First…some theory:

There are two types of air injection widely used. On automobiles, a compressor is used which has different functionality than pulse air injection widely used on new closed loop EFI motorcycles. Pulse AI gets its name from the engine firing and exhaust pulses. When pistons go up in unison on a vertical twin for the exhaust stroke, this creates an air percussive pulse (wave) out of the combustion exhaust ports with velocity and momentum based upon no. of pulses per minute i.e. one half of engine RPM e.g. 4 cycle. In a closed volume, if an open orifice is upstream of this exhaust wave or pulse e.g. air injection tube….with a fresh air source available e.g. airbox, this draws...due to vacuum ...not injects (which would be positive pressure) air into the injection tubes which then is drawn into the headers to join the flow of pulsing exhaust air being emitted from the exhaust ports. So air is really drawn by vacuum into the air injection tubes, not injected under positive pressure per se…hence air injection is really a misnomer. This additional cooler air supplemented to expulsion of fuel from the exhaust ports into the headers when the throttle is closed in combination with hot headers due to combustion creates a more complete burning of fuel for reduced emissions.

The ECM only energies the solenoid to allow air into the exhaust ports at small throttle openings but also senses its presence by virtue of it solenoid resistance. The solenoid registers 20 ohms of resistance when measured with a multimeter. Without a complete circuit with resistance, the ECM will throw a code and initiate a check engine light (CEL). Both an open circuit and shorted circuit have been tried and each result in a CEL on the new EFI bonnie.

Some inquiring minds may want to know how substituting a resistor satisfies an ECM. Pretty much all interfacing components with the ECM are either fixed or variable resistors. This is how the ECM processes its information. A solenoid is a linear motor with an electromagnet comprised of a helix of effect, a resistor not unlike the ceramic covered wound wire resistor used for this DIY to replace it. Difference is is how the energy is dissipated. Basically an ECM is a microprocessor with a number of integrated MOSFET’s. MOSFET’s are semiconductor transistors used for voltage comparator circuits. ECM’s contain thousands of these decision making devices. The way AI works is…the the TPS tells the ECM the rider has let the throttle return to idle. O2 sensors go into open loop and don’t talk to the ECM which defaults the A/F mixture to a baseline map based upon information from the air temp sensor. The TPS in idle position causes the the ECM to send current to the solenoid...about .6 amps…to engage the valve and draw air from the intake into the exhaust ports. During this time the ECM evaluates the voltage due to change in current and compares it to a programmed upper and lower limit based upon MOSFET selection. If the voltage is too great or too small, it will gate the current to deploy a CEL and reset the A/F map to limp mode or open loop. That is how a circuit can both operate a solenoid and also simultaneously detect proper amount of voltage for upper and lower limit. By substituting a resistor, the circuit when activated by the ECM will still compare voltage however will no longer effect any mechanical change i.e open a valve…as the ECM interprets the resistor as a solenoid. A simple calculation suggests that a 50 ohm resistor will reduce current to .24 amps = 2.88 watts of power which will be dissipated in terms of heat versus work done to move an electromagnet opening the valve. Choosing a 10 watt 50 ohm resistor, not only reduces current still acceptable to the ECM, but also emits a modest amount of heat energy easily contained by the relatively large heat sink based upon its intentionally oversized 10 watt thermal mass capability.

OK…how to remove AI from EFI bonnies:

To begin…Richard and Dick need to be credited with a DIY to remove the gas tank on EFI bikes seen here:

Further, Dick is to be credited with the first to my knowledge to both remove AI and add a Power Commander III to a new EFI bike…Dick has two new EFI bikes in this configuration in fact. So Dick really started the ball rolling with removing AI initially. One of the things we have learned since then is…you don’t need a Power Commander to remove AI. Many owners started taking the AI’s off EFI bikes either with the base map or one of the optional maps. Some got CEL’s because they went a step further and removed all the plumbing associated with AI including the solenoid. I like clean so that means all the plumbing must go.

Let’s get started.
First remove the tank…how it looks with the tank off and AI plumbing in place
Most of the stuff shown in the picture will be removed:

Next unplug the large hose that draws air from the air box.

Last edited by biker7; 06-18-2009 at 10:59 AM.
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Old 06-18-2009, 09:06 AM   #2 (permalink)
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The airbox plug comes with the kit. I chose the flush mount AI kit from British Customs because I believe it has the cleanest look:

Next…remove the air injection tubes adjacent to the spark plugs. The plugs btw do not have to be removed for this in spite of instructions that suggest otherwise. In the common practice of wrenching…one always tries the least invasive method of tearing down a motor. In the case of these insidious tubes which are positioned very close to cylinder head casting material…access to the 13mm hex is tight. I thought I would be clever lightly kiss a ” open end wrench with a die grinder to take it to just under 13mm but found the torque to be too great to remove the tubes without rounding the hex which I absolutely did NOT want to do.
This is what I tried first:

Some have successfully used a ring or box end wrench which offers better engagement. I believe an offset box end wrench would work as others have reported but I knew a 6 sided deep socket would be best. Unfortunately, I couldn’t find even a special deep socket deep enough so like others before me, I elected to break off the tubes which is quite easy.
First kink the tube with wire cutters:

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Old 06-18-2009, 09:07 AM   #3 (permalink)
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First, remove the rubber tubes by taking a small blade screwdriver and drive down the Oetiker clamp holding the rubber hose to the metal injection tube. The rubber tubes will now lift right off. I believe the Oetiker clamp could be used again but installation would be more difficult. A simple substitution with a std. small hose (worm gear) clamp would do. Then I took a large philips screwdriver shank and fatigued the tube(s) off. This is very easy to do. You now can use a basic 13mm deep socket. Btw…I suggest a 6 sided versus 13 sided socket for this for maximum engagement. Again…the tubes in this case were sacrificed but I knew that AI wouldn’t be going back on my bike.
See pic with extension added. I used a ” drive rachet for increased leverage.

I am glad I went this route and this is still the path I recommend to everybody as extracting these tubes takes a fair amount of torque and you don’t want to round the hex on the injection fitting or you are hosed…forgive the pun. For those that want reversibility…purchasing these small metal tubes either from the dealer or a Rat member is still likely cheaper than a special 4” deep well socket from Snap On. If a special socket like this does exist…I couldn’t find on in my brief search, it would likely cost more than replacing the tubes…lol.

OK…on to installing replacement plugs. I like clean if not elegant solutions and British Customs makes some sweet AI plugs for these motors without protrusive hex heads. Always use a copper washer and a hint of anti-seize paste on the threads as you never want steel and aluminum to get too cozy due to heat cycling:

And how they look installed in the bike. The look is outstanding. Couldn’t be happier with the access to the plugs or how factory it looks:

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Old 06-18-2009, 09:08 AM   #4 (permalink)
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On to the second part which is removing the plumbing from the bike. This part is pretty easy…bolts on both sides of the top frame rail and the whole mess comes off. Ok…now you have the injection tubes removed and holes plugged…the airbox plugged and all the AI plumbing removed…now its time to address the electrical aspect of AI that interfaces with the ECM via the solenoid that no longer is on the bike. As previously mentioned a 50 ohm 10 watt resistor will do nicely as a surrogate for the solenoid. These are cheap and inexpensive and available at Radio Shack. This keeps the ECM happy and satisfies the diagnostics of OBDII.

The next part of the DIY relates to how to mount the resistor to the bike’s harness. The further invasive nature of this DIY relates to the solenoid connector. Dick and I have had a fair amount of discussion on this and have concluded that cutting off the connector is the best approach because using stand alone pins plugged into the factory female connector would not be very robust and you don’t want to lose continuity to the resistor that replaces the solenoid.
A look at the solenoid connector after cutting it off which exposes how small the pins are:

Further…reversibility is not big deal as the connector can be restored almost imperceptibly with a little solder and shrink tube in the event you wanted to put AI back on the bike…heaven forbid.

OK…you will want to prepare the resistor for installation. I elected to have both leads go on the same side and for stealth, use shrink tube to bring them together and then stagger the connectors to further minimize package size on the bike.
How the resistor looks prepped with pigtail and male bullet connectors:

For attachment…I connected the resistor to the large cord of wires comprising the harness via a single tie strap and some electrical tape for further insulation.

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Old 06-18-2009, 09:09 AM   #5 (permalink)
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The end result with robust bullet connectors available again at Radio Shack which I have used over the years on other motorcycles for many wiring applications…turns out to be hard to even detect after the installation is complete. If you didn’t know a resistor was there, you would be hard pressed to see it…even with the tank off. You can feel the resistor for heat and it doesn’t get hot as the ECM only occasionally looks for the solenoid and when it does..with very little current due to the generous resistance and 10 watt load capacity of that resistor.

Last edited by biker7; 06-18-2009 at 09:27 AM.
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Old 06-18-2009, 09:11 AM   #6 (permalink)
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Lastly…how does the bike run without AI?. In summary, the rideability of the bike is improved.

Changes to the bikes performance without AI:

- No change to acceleration

- Softer throttle onset…throttle modulation feels more like carbed Bonnies with less abruptness or the term of snatchiness often used to described EFI throttle response.

- Occasional backfiring i.e. sucking of exhaust into intake completely gone.

- Popping “completely eliminated” on decel. This again is with stock factory map and Tors exhaust. Prior to AI removal I would experience light popping most of the time when closing the throttle.

Best Regards,,

Disclaimer: I am obligated to conclude this DIY with a cursory disclaimer relative to a modification of this nature. This DIY is for off road use only and I accept no responsibility for any effect this change has to the performance or function of your bike or effect on the environment. Implementation of this modification is at “your discretion only.” Providing this thread is for information purposes only to help others that are so inclined. Above all…ride safe.

Last edited by biker7; 06-18-2009 at 09:27 AM.
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Old 06-18-2009, 10:35 AM   #7 (permalink)
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Great write up George! The pics will make this a lot less daunting for many others. Mine is almost identical; I used a two pin Molex connector I had laying around instead of the bullet connectors. I ran a digital ammeter through the circuit for a few days to see what the peak reading was while riding and it never went over 200ma so I guess we are fine with our 10W resistors. I am going to continue to look for the mating connector for the AI solenoid loom, as it exists somewhere and if it can be located someone like BC or New Bonneville could offer a nice 2009+ AI removal kit with a pre-wired plug and play connector/resistor.

A warning to others: Do not turn on the power or run your bike with the AI solenoid connector demated or without the resistor or you will be enjoying a nice bright orange check engine LED until you clear the code - ask me how I know this
'09 T100 50th Anniversary- Togas, Hagons, PC V
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Last edited by dkreidel; 06-18-2009 at 12:09 PM.
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Old 06-18-2009, 10:49 AM   #8 (permalink)
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Thanks fr your great effort

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Old 06-18-2009, 10:51 AM   #9 (permalink)
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Thank you Dick. You are in large part responsible for contributing knowledge about the EFI bikes and a pioneer in removing AI so thanks to you for your information sharing that contributed to this thread. Thanks also for measuring the amp load...ECM now only is testing the circuit which apparently draws very little current...a good thing for a cool running resistor.

Also, this DIY is meant as a working document so please weigh in with your questions and in particular your experience if you choose to remove your AI on your EFI bike.

A couple of further comments. Thanks again to Dick, Frank and others, it has pretty much been concluded that US spec EFI bonnies don't have cats in the headers. It seems as though European spec bikes "may" indeed have cats in their headers which changes the landscape for deciding to disable AI.

Second issue is...AI has and can be successfully removed by just leaving the solenoid in place and attached to satisfy the ECM. The rest of the plumbing can be removed. This simplifies the DIY and also helps reversibility and is almost as clean.


Last edited by biker7; 06-18-2009 at 10:55 AM.
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Old 06-18-2009, 12:17 PM   #10 (permalink)
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Nice job, George, both in the doing and in the illustrated write-up.

Since you mentioned the turn signals, which are they? I'm not highly motivated to change mine for visibility reasons, but I do like yours.
2005 Bonneville Blue 790cc, AI removed, Staintunes RC, no snorkel, inlet enlarged, 118/40/NBZT "Thruxton" needles/1 shim/3 turns, Ikon 7610s, Ricor Intiminators, Dunlop GT501s, D9 gauge panel, tachometer.
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