Fast Idle Circuit and FI Enrichment

[Denver_FJR]

Recently came across RadioHowie's great post about the FJR's fast idle design. It appears it's simply mechanically controlled valves that allow additional air during cold start. So where does the extra fuel come from? I know it's from the injectors (duh) but how does the FI system "know" how much extra fuel to deliver and for how long. My thought is the MAP sensor is the only input the ECU has while the system is in open loop, but I've seen several posts from those who have disconnected their MAP sensor and noticed no change. (Maybe those where short tests only performed post warm up?)

Thoughts?

 

[SkooterG]

What's a MAP sensor?

And you need to be careful as the Gen II fast idle system, at least how it is activated, is completely different than the Gen I.

 

[RadioHowie]

MAP sensor = Manifold Absolute Pressure sensor...it's the vacuum sensor attached to the fuel rail on the left end, if viewed from the driver's seat, looking forward.

Skoot, looking at the parts fiche for an 07, the fast idle system is identical to the Gen 1, i.e., a wax motor heated by coolant, to open/close the air valves on the throttle bodies. Probably the only difference between Generations is the speed of the fast idle, lower to account for AE operation.

As to the OP's question, I'd hazard a guess that coolant temperature is probably the determining factor in the injection/fast-idle loop.

 

[SkooterG]

MAP sensor = Manifold Absolute Pressure sensor...it's the vacuum sensor attached to the fuel rail on the left end, if viewed from the driver's seat, looking forward.
Skoot, looking at the parts fiche for an 07, the fast idle system is identical to the Gen 1, i.e., a wax motor heated by coolant, to open/close the air valves on the throttle bodies. Probably the only difference between Generations is the speed of the fast idle, lower to account for AE operation.

Well, then I guess they changed it in 08. Because when I helped Fairlaner do a valve check on his 08 the fast idle circuit was completely different.

Edit: Never mind. I was having a 'moment'. The normal idle circuit is completely different on the Gen IIs than the Gen I. I guess the fast idle circuit is the same.

 

[RadioHowie]

MAP sensor = Manifold Absolute Pressure sensor...it's the vacuum sensor attached to the fuel rail on the left end, if viewed from the driver's seat, looking forward.
Skoot, looking at the parts fiche for an 07, the fast idle system is identical to the Gen 1, i.e., a wax motor heated by coolant, to open/close the air valves on the throttle bodies. Probably the only difference between Generations is the speed of the fast idle, lower to account for AE operation.

Well, then I guess they changed it in 08. Because when I helped Fairlaner do a valve check on his 08 the fast idle circuit was completely different.

Well, that's weird. All years of parts diagrams show the same fast idle circuit. But I am telling you the fast idle circuit on Fairlaner's 2008 FJR was nothing like the fast idle circuit on the Gen I. For example, NO coolant lines or wax motor. Seems Yamaha didn't correctly update their parts diagram?

What??? Yamaha screw up??? Well, yeah, there IS that whole "Gen II" thing.....

 

[SkooterG]

As to the OP's question, I'd hazard a guess that coolant temperature is probably the determining factor in the injection/fast-idle loop.

I bet engine RPM plays a big role too......

MAP sensor = Manifold Absolute Pressure sensor...it's the vacuum sensor attached to the fuel rail on the left end, if viewed from the driver's seat, looking forward.
Skoot, looking at the parts fiche for an 07, the fast idle system is identical to the Gen 1, i.e., a wax motor heated by coolant, to open/close the air valves on the throttle bodies. Probably the only difference between Generations is the speed of the fast idle, lower to account for AE operation.

Well, then I guess they changed it in 08. Because when I helped Fairlaner do a valve check on his 08 the fast idle circuit was completely different.

Well, that's weird. All years of parts diagrams show the same fast idle circuit. But I am telling you the fast idle circuit on Fairlaner's 2008 FJR was nothing like the fast idle circuit on the Gen I. For example, NO coolant lines or wax motor. Seems Yamaha didn't correctly update their parts diagram?

What??? Yamaha screw up??? Well, yeah, there IS that whole "Gen II" thing.....

Never mind. Me screwed up. I know - imagine that? First time this millennium.

 

[SLK50]

Don't worry, the millennium is young, you'll have plenty of opportunity.

 

[Fred W]

The ECU adds the extra fuel during cold starts in the form of prolonged injector open time.

Even if the wax motor didn't add the extra bypass air to increase cold idle speed the ECU would be adding extra fuel during warm-up based primarily on the coolant temp sensor signal, but it is also affected by the increased intake air volume, which is calculated from the TPS signal and the Intake air pressure sensor.

The ECU also has a special Starting Injection condition where it squirts a bunch of fuel in asynchronously (not timed to crankshaft position) to aid in starting while cranking. This is the feature that can cause your engine to flood if you keep trying to start it over and over, or turn the engine off too soon after a cold start.

Basic injector duration is always being adjusted based on a few of the signals: intake air temp, engine rpm & TPS. Anyone else think that sensor might be important? Not as important as Seafoam, of course.

 

[RadioHowie]

The ECU adds the extra fuel during cold starts in the form of prolonged injector open time.
Even if the wax motor didn't add the extra bypass air to increase cold idle speed the ECU would be adding extra fuel during warm-up based primarily on the coolant temp sensor signal, but it is also affected by the increased intake air volume, which is calculated from the TPS signal and the Intake air pressure sensor.

The ECU also has a special Starting Injection condition where it squirts a bunch of fuel in asynchronously (not timed to crankshaft position) to aid in starting while cranking. This is the feature that can cause your engine to flood if you keep trying to start it over and over, or turn the engine off too soon after a cold start.

Basic injector duration is always being adjusted based on a few of the signals: intake air temp, engine rpm & TPS. Anyone else think that sensor might be important? Not as important as Seafoam, of course.

"HE SHOOTS!! HE SCORES!!!"

"GOOOOOOOOOOAAAAAAAAAALLLLL!!!"

 

[ionbeam]

Not quite as important as Seafoam is the Intake Air Temperature Sensor. So, we know coolant temp, air temp, intake pressure (Gen I also knows atmospheric pressure) (Gen I fuel rail pressure) and Throttle Position. Add some lines of software code and VAROOOOM, we are off. In addition to all these fuel thingies we are listing, the ECU will be changing the normal spark timing curve.

 

[Fred W]

The ECU also (apparently) compensates for battery voltage in the FI duration according to the 1st Gen FSM, though it isn't clear exactly how or why to me. Perhaps the baby seal killer is onto something important?

Spoiler

NAH!

PS - I did mention the IAT sensor already, Professor, but not the atmospheric pressure sensor, which is very important in the air volume calculation that I mentioned, since the manifold air pressure has to be corrected for ambient to get anything meaningful.

 

[ionbeam]

Ahh, posting in haste, I missed the IAT. With no Mass Air Flow sensor the ECU has to do a little extra work, thank goodness it is usually good at math. I was going to PM you but I'm still in a time crunch, so I'm posting the following...

At 10k rpm the injectors are firing ~42 times per second. I assume the injectors are poppet type solenoids and not modulated by voltage/current. Your opinion? Monitoring battery voltage is a way to determine if there is sufficient 'pull-in' voltage, or over voltage which could damage the injector. During cranking with a Shorai battery when voltage drops below (?) 8.x volts the ECU stops firing the injectors because cranking RPM would be too slow to start (?) and the injectors would be approaching minimum pull-in voltage (?). My, guessing is such fun! Without actual facts we get to make up the story so it should have a happy ending. But, we can get closer to the truth by bundling what facts we do know.

 

[J Paul]

All the gasoline or gaseous fuel injectors I've ever worked with-Cummins heavy duty and midrange engines-use a PWM signal with dedicated drivers in the ECM.It's been explained to me that voltage drop effects the drivers before the computer causing mismetering.

 

[Redfish Hunter]

This is all such good technical sounding stuff. I am sitting here drinking a Seafoam and Ring-Free cocktail and reading all this knowledge. The more Seafoam I drink, the more sense it all makes.

 

[ionbeam]

This is all such good technical sounding stuff. I am sitting here drinking a Seafoam and Ring-Free cocktail and reading all this knowledge. The more Seafoam I drink, the more sense it all makes.

Now here is a smart guy, I'm off to the garage to mix a few too. I'm thinking a good brake fluid shooter should cap it off, after all we need to know when to stop.

 

[Fred W]

I've never been particularly good at that (knowing when to stop). This post is Prima facie evidence of such.

 

[Redfish Hunter]

I've never been particularly good at that (knowing when to stop). This post is Prima facie evidence of such.

In that case, let us both take a lesson from our friend Ionbeam. A small addition of brake fluid will most assuredly enhance your ability to stop. Unless of course, your ABS has created bad habits or your caliper pistons have become discolored. In which case, you might need to watch this video I JUST found of an FJR rolling off a dock...
In fact, I apologize to the OP for diverting this thread with my useless drivel. I will just have some of that brake fluid now.

 

[Denver_FJR]

In fact, I apologize to the OP for diverting this thread with my useless drivel. I will just have some of that brake fluid now.

Heh, I knew what I was getting into. Pass the brake fluid shooter along!

 

[Chuck35]

One of the reasons car makers started triggering ignition coils from the ecu many moons ago was so they could increase the dwell (duty cycle) when the battery voltage was low to still have a nice fat spark.

The ECU also (apparently) compensates for battery voltage in the FI duration according to the 1st Gen FSM, though it isn't clear exactly how or why to me. Perhaps the baby seal killer is onto something important?