Tempurature Sensor Mod

Here is the problem. My '09 FE450 runs great for about a hour or maybe two. Then it starts to hesitate and sputter randomly. If the bike cools off, it runs great again, so it appears I have a heat soak problem. It is not the gasoline overheating since refilling the tank with fresh, cool gas does not help. The engine itself is not overheating, the cooling system is fine. However, the rest of bike gets really hot, including the rubber airbox.

The air temperature sensor it mounted in the bottom of the airbox, which happens to be very close to the exhaust pipe. This is actually a very poor location for it for a couple reasons. First, the sensor itself will get a substantial amount of heat from the exhaust and engine. Also, the location of the sensor will not always be "cooled" by the incoming air flow into the engine since it is not in the path of the air flow. This problem will be worse if you are riding slowly with low throttle for extended periods since the air box may not be mixed up enough to get an accurate temperature reading. Under these conditions, the temperature sensor will be reading too high, which will generate an incorrect lean condition since the actual air entering the engine is much cooler.

The solution? Every other FI vehicle has the air temp sensor directly in the airflow to the engine where it will have the best reading. My fix is the move the sensor to the intake boot. I simply removed the sensor, extended the wiring, drilled a hole into the intake boot, inserted the sensor into the hole, and zip tied it in place.
See the attached picture.

The results? My bush whacking adventure last week proved that it worked, the bike ran fine the entire day.

Kayeffess said:

Looks great Brian. Seems to make a lot of sense too. Giving the computer the actual temp of the air going directly in the intake. Did you change the plug to find out if it is running lean or fat?

Click to expand...

Plug reading is witchcraft. I guess I could have taken a reading off the O2 sensor, but I just wanted to test my theory. It was easy enough to switch back to stock if it didn't work. Seems to work great, bike got really hot in the last Ganny ride, lots of downed trees to jump over.

OK, it seems that this mod did NOT completely fix the problem. Bike still was running crappy when it got REALLY hot.

On next thing to check: The Throttle Position Sensor (TPS) voltage.
Stock setting is 0.60V at idle. Mine was dead on. However, there was some talk about adjusting the TPS to give 0.64V which should provide a slightly richer mixture at idle.

I adjusted the TPS, took it for a spin and it was better, but not perfect. Back at the garage saw 0.63V on the voltmeter. I also got the bike hot to see if the voltage changed as the sensor got hot. There was no change.

A quick adjustment to 0.65V, another test ride, and the bike seemed to be running much better when it got hot. I would say it runs 95% better. I just have the occasional pop on decal, but it didn't flame out, run rough or be hard to start.