Idling -- '13+ FJRs vs earlier models

[Constant Mesh]

One thing I've never understood all that well on my '04 is the idling fluctuation.

I can finish a nice hour ride, pull into my drive, observe a smooth idling engine @ 1.1K rpm for a few seconds and then shut it down.

I can come back fifteen minutes later with the bike not having cooled all that much, start it and observe the idle speed being quite a bit lower and somewhat erratic. I don't understand why the speed has dropped down below 1K.

The coolant temp is still two bars. The wax motor idle control is not in play.

Why has the computer reduced the fuel input when the temp and other inputs would indicate a warm, up to temp engine?

I envy those with the '13 and later FJRs. I'm assuming your idle rpm is rock steady and precise once the engine is up to temp. The computer measures the rpm and adjusts the throttle valves to get the desired idle speed.

 

[dcarver]

My 13 FJR still fluctuates idle rpm even after full warm up.

My DL650 Suzuki is rock steady.

My 2006 FJR fluctuates too.

Must be an FJR thing.

 

[RaYzerman19]

If throttle sync is OK and no vacuum leaks..... perhaps the fuel in the tank gets a chance to warm up while sitting? Air box temp sensor warmed up too? All that heat has to go somewhere. I haven't noticed much of a problem.....

 

[Queensland Ken]

The FI system is explained in chapter 1 of the service manual.

It's to do with fuel enrichment during a cold start, governed by coolant temp and less fuel on a warm start.

 

[lele]

dirty throttle bodies?

 

[ionbeam]

Older electric tachs would use the ignition signal to drive an averaging volt meter (gross simplification, one type of meter), these meters were often damped to eliminate little variations and ticking of the needle. This also resulted in an artificially more stable tach needle.

The FJR ECU sends a digital signal to the meter assembly (dash gauges) and drives a stepping motor which is not as damped as an analog type gauge. Yamaha could have added some digital filtering to stabilize the tach, depending on how it's done it could slow down the tach's responsiveness.

I have found that a TBS will affect how stable the idle is with temperature variation and how repeatable it is from warm start to warm start. I haven't tried to correlate barometric pressure or altitude to the tach stability

Warm air and higher engine vacuum tend to contribute to tach needle wander. A rich, lower vacuum engine tends to have a more stable idle.

The FJR, like most performance motorcycles has a very light flywheel weight which contributes a lot to tach variation. Most performance engines idle at very low load so there is little damping, unlike a car with a big ol' flywheel. The engine is also run fairly lean which causes higher intake vacuum which contributes to tach variation. As lele mentions, a dirty throttle body can also contribute to wandering idle.

Is the idle sufficient that the engine idles without stalling? Is the idle low enough that the ECU isn't hunting the FI up and down? (With an engine up to operating speed, try holding the throttle steady around 1,700 for a minute or so and see what starts happening to the idle speed.)

My '04 idles pretty stable and may vary 50-100 rpm, depending on engine and air temperature. I still can sleep at night and don't feel a need to disassemble the engine to fix this 'problem'

 

[lele]

ionbeam why are u so smart?

 

[its just rain]

He must be really old

 

[ionbeam]

He must be really old

At least this part is verifiably true.

 

[wheatonFJR]

He must be really old

After having observed various groups of this Forum population in various settings, I can positively conclude that age and smarts do not necessarily have a 1:1 correlation.

Ionbeam's other worldly smarts are proof of the existence of alien implantation on this planet.

 

[15wannabe]

Hey Mesh, might be something as simple as the engine being "heat soaked". You've turned it off and the coolant is no longer circulating. I read somewhere that heat soaked fuel injected engines will "lean out", while carburated engines richen during the same process.

 

[huron52]

I just tell people that I have put a high lift Cam in it.....