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2009 Buell 1125R Rear Fuel Injector Disconnect


Obviously, try this at your own risk, I am liable for nothing.

I may have found a solution for excessive engine heat in stop and go traffic. I first partially tested this idea while I was removing the throttle solenoid and the official useless stator harness "fix". Since I already had the air box off, I decided to unplug the electrical connector to the rear fuel injector. I started the bike, the ECU detected the error, and the bike continued to run on one cylinder. I turned off the bike, reconnected the rear injector, and started the bike. It ran fine and showed no check engine light or fault. So, the question was: Can the rear fuel injector be switched on and off while the bike is running?

This summer's 100+ degree F heat and stop and go traffic around San Antonio proved to be the motivation I needed to answer that question. I installed a switch in series with the rear fuel injector. This reduces fuel consumption and therefore heat generated while idling. This also increases cooling capacity by drawing air, without fuel or combustion, through the rear cylinder. Luckily, the ECU is smart enough to keep the bike running on one cylinder and the check engine light disappears when the rear fuel injector is turned back on. The rear fuel injector can be switched on and off while the bike is running.

In the video below, ambient air temperature was about 105 degrees F. At the start, the bike is idling normally on both cylinders and you can see the coolant temperature continue to climb. If I were riding in stop and go traffic, the coolant temperature would climb to at least 220 degrees F. Then I switch the rear fuel injector off and the ECU shows two errors: rear injector fault and rear O2 sensor fault. Afterward, the coolant temperature drops by 10 degrees F in 2 minutes or so. I rev the engine on one cylinder to show that it is still usable. Next, I switch the rear injector back on to show that the ECU extinguishes the check engine light and the bike runs on both cylinders, which you can hear immediately after the injector is switched back on. Finally, the coolant temperature climbs again while idling on two cylinders. I actually drove the Buell for a few miles on one cylinder and it worked, but it felt much slower. The sound and feel were quite a bit different, because it was essentially a 562cc thumper, and it required much more throttle and higher RPMs to get it to move, but it will work great in hot stop and go traffic.

This is not a novel idea; HD has been doing this automatically in their ECUs for years. They call their automatic cut-out feature EITMS or "parade mode".

Accelerated Testing 9/1/2011

I rode 30 miles today on one cylinder and another 10 miles on two with deactivation at stop lights. I had planned on 300 miles on one cylinder, which is 10% of a 3000 mile oil change, but I have to cut it off at 30 miles or 1%.

Riding around on only cylinder is not fun at all; go figure. ;) It has no torque at low rpm, it is not smooth at low rpm, and it sounds half castrated. Once I was moving, everything was fine and smooth enough. My momentum and the wheel speed functioned as the larger flywheel single-cylinder operation needs. I did some stop and go and some highway at about 65 mph. Starting from a stop is tricky; it requires high rpm, like 3-4k+ RPM, just the right amount of clutch slip, and a lot of throttle. Taking off from a stop on one cylinder, I feel like I will eventually stall it out when I need to get moving, which is not the safest feeling. So, I cut the riding on one cylinder part of the test short. This should still give some good accelerated reliability data for the mod because of the torque and RPM involved.

For the 10 miles on two cylinders on my way home today, I flipped the switch at every stop light. Idle RPMS drop for a fraction of a second until the computer compensates. When operated this way, this mod rocks. My coolant temperature was 215 F, at 100+ F ambient, when I pulled up to the longest light. I have to sit through at least 4 light cycles at this one, inching up bit by bit, but it is still the fastest way home. My coolant temperature dropped to 195 relatively quickly. My frame was noticeably less hot.

Putting Heat In Perspective

Yes, this is a pic of my melted and deformed ear plug case. It hangs forward of the ignition switch getting lots of radiator/convective heat and touching the frame. This happened some time in the last two weeks, but I just noticed it this morning.

Automatic Operation

Several people over at BadWeB suggested that the manual toggle switch is a bad idea and are right on the money. A couple of times, I had inched my way up to the light on one cylinder. When the light turned green, I switched the rear cylinder back on and started to move. But, I waaaaay over revved the bike because I had given it too much throttle and too little clutch. Darn muscle memory; and this was when I was paying close attention.

My next move was to convert from the toggle switch to a normally-closed relay driven from the neutral light or the neutral wire coming out of the transmission. This only cuts the rear fuel injector when the bike is in neutral. I used the toggle switch to enable or disable the neutral light to relay connection. This is automatic, does not require any extra controls, and inching up in traffic happens on two cylinders.

Here is the relay I used:

First, I made a some electrical measurements at the neutral switch connection:

Next, I connected a diode in series with the existing neutral switch wire to protect the ECM from the 12V used in the modification. Yes, I know this diode is probably overkill, but I wanted to keep the voltage drop from the ECM current extremely low. I tapped a new neutral wire in after the diode.

After running the new wire to the front, I tested to make sure the ECM, neutral light, and relay all still worked properly with the engine not running. Alligator clips are great for this.

I used a mini fuse tap (add-a-circuit) in the fuse box under the seat in the key-switched ACC position to power the relay. I also used this to power a HomeLink universal remote I purchased on Ebay from a Land Rover.

This pic shows the toggle switch and the HomeLink remote mounted:

Here is a simple wiring diagram of what I ended up with:

Here is a video of this modification in operation at idle. Notice that there is little to no noticeable hesitation when shifting from 1st to 2nd gear.