Considering a different take on abrubt throttle response due to Yamaha fuel cut off when coasting in gear

[SnowmobileGuy]

I have a 2006 FJR1300A. Like many of you, I don't appreciate the abrupt throttle response when rolling on the throttle after coasting in gear with the throttle off. There are a bunch of fixes out there that mitigate the issue to varying degrees - Barbarian mod/CO, throttle spring removal, throttle body sync, G2 throttle tube, removing throttle cable free play, PCIII/PCV, etc. They all seem to help some, but there are some folks out there that can't get the issue resolved to their satisfaction with those fixes (either singly or in combination). I contacted Dynojet and they indicated that there Power Commander can not completely eliminate the issue because the Power Commander doesn't stop the fuel from shutting off. You can smooth out the response once the ECU tells the injectors to open, but the fuel will still be cut off when coasting in gear with the throttle off. That got me thinking along a different track.

There are only a few ways the ECU can sense that you are coasting while in gear. The maintenance manual does not have an FI system flowchart - it just focuses on trouble shooting tables and wire diagrams. One must infer the system logic. It knows what gear you are in, it knows your speed, it knows throttle position, manifold pressure, air temperature, etc. It also knows when the clutch is pulled in, but the FI system doesn't show that as an input (it's used in the starting circuit). My thought is this: How about tricking the ECU into thinking you never close the throttle. It seems this could be accomplished by advancing the TPS adjustment just a bit above spec. There might be a risk of running a bit rich if the ECU relies heavily on the TPS reading for injector timing and thinks the butterflies are more open than they actually are. If it primarily relies on engine speed, manifold pressure and temperature, and air mass flow, it might not be a big deal. Perhaps there is a proper median there somewhere - that is, just a few degrees of TPS advance above spec might be tolerable as far is stoichiometry is concerned, but still fool the ECU into thinking the throttle is not shut off. If this were to work, you would have to drop the idle speed a bit (with the idle adjustment knob or the air screws). Is my logic flawed? Has anyone tried this? I'm planning on trying it, but wont be able to get to it for at least three weeks.

 

[Fred W]

I like your train of thought here.

If you already have a PCIII you could compensate for the advanced TPS by subtracting a little fuel from each cell.

Subscribed to hear your results.

 

[wfooshee]

I'm not sure it's not necessarily only at shut-off. Anytime the engine is being "dragged" by the bike's own momentum you have the potential for fuel shut-off, whether the throttle is actually closed or not. In other words, the bike is already going faster than the throttle setting.

Also, I'm not sure raising the TPS minimum would do anything. I'm not sure the ECU wouldn't adjust for it. "Hey, I've not seen anything lower than X from that thing for a while, that must be fully closed, then."

Mind, I'm in a complete fantasy guessing world here.

 

[lnewlf]

It's all in the wrist...

Some company makes a fuel cut eliminator but I don't think they are available for the FJR..

 

[SnowmobileGuy]

As far as "...all in the wrist", that is true, but I want the calibration it to be as good as my other bikes or my cars. It is also wildly different from my other bikes and the differences are hard to adapt to when switching from my other bikes to the FJR.

Wfooshee, I'm not convinced the ECU understands the situation you are describing. Shutting the fuel off at anything besides closed throttle sounds dangerous and counter to what the throttle is for; that is a torque request. The throttle is not a speed request. I don't ever recall experiencing such a situation. If I suddenly go from flat land to a downhill and keep the throttle the same, the bike accelerates (i.e. momentum is transferred from the earth to the bike). Can you further describe the situation you have experienced?

 

[SnowmobileGuy]

Inewlf, Ivan Performance Products has the fuel cut off eliminator for other bikes, but not the FJR.

 

[wfooshee]

I didn't say I've experienced it, I just meant that I could visualize fuel flow being cut off if the ECU saw no need for fuel. It wouldn't happen at the same wrist position you started your downhill at, although fuel flow could be reduced, but as you back off the throttle, a clear signal to the ECU that force is not required, I can see it shutting off the injectors, perhaps only momentarily, even with the throttles still open. As you close the throttle further, the shut of could last longer each time.

It's not so much an efficiency motivation as an emmissions motivation on the part of the ECU programmers. No fuel, no smoke, no emissions!

And like I said, I have no knowledge that such programming occurs, opnly that I can see how it would, and I repeat my "just guessing" disclaimer.

 

[Chuck35]

If the issue is mostly at accell after coast from FULLY closed throttle, there may be a switch in the tps that can be fooled without changing the adjustment across the range.

In the cars I am familiar with this is an NC switch that is opened at idle.

 

[BobQ]

In the 0% throttle cell add 10% - 20%. Anything less than 1500 rpm or so leave alone, it will run like a carbureted bike! They use to call it dry stacking, I think anyway. I had a thread about this back in 09 but can't find it. Report back and tell us how it rides. Start at 10% and work up!

 

[SnowmobileGuy]

Chuck35,

I don't recall seeing a switch (normally closed or open) in the wiring diagram. I will look again. I did check impedance and voltage and they were within spec.

 

[SnowmobileGuy]

BobQ,

I don't presently have a PC. My idea is to cheat the EFI with a tiny advance of the tps and hope I don't make it too rich.

 

[ionbeam]

If the issue is mostly at accell after coast from FULLY closed throttle, there may be a switch in the tps that can be fooled without changing the adjustment across the range.In the cars I am familiar with this is an NC switch that is opened at idle.

No switch in the TPS, and the TPS doesn't work like this. There is no help or solution from TPS settings. On the road to CFR and the POS computer I'm using is making a full reply a pain in the ass.

 

[gixxerjasen]

While I'm no fan of his, I've often wondered why Ivan hasn't developed and sold an FCE for the FJR. Seems to me that with the FZ1 and the FJR both getting redesigns for the 2006 model year, that the fuel cut would have been added to both bikes since they both suffer the same problem it seems.

 

[SnowmobileGuy]

"There is no help or solution from TPS settings. "

Then the question is how does the ECU know when to shut off the throtle? It needs signals from more than one sensor to determine this.

 

[wfooshee]

I think your post scrambled, and the last sentence is you, not ionbeam.

And I think you're asking how the ECU knows when to shut off the fuel.

The fuel injectors are not analog, they are digital, i.e. they are on, or they are off. There is no "on a little bit" or "on full blast." They don't flow fuel faster to get more, they flow fuel longer to get more. The only way to decrease fuel flow is to STOP fuel flow.

Whenever the ECU determines that there has been enough fuel fed, it shuts of the injectors. That might be for milliseconds, it might be for several seconds.

The sensors on the bike related to fuel flow are throttle position, air temperature, air pressure, engine speed, and oxygen in the exhaust. The ECU factors in vehicle speed as well, I'm sure. Very low throttle position, fairly high speed, means very low fuel flow, or even no fuel flow. Reading the speed may be that "other input" you're looking for. Closed (or low) throttle coasting at 60 mph needs no fuel delivery. Closed throttle and 0 mph needs fuel to maintain idle. The difference is how fast the bike's going.

 

[SnowmobileGuy]

Wfooshee,

In my post to ionbeam I screwed up and for some reason the edit button doesn’t show up.

The injectors are actually not digital. There is a transient component in their performance. There is basically an "attack", "sustain", and "decay" phase when they are fired, but true, you can't tell the injector to partially open. The hope is that the fuel volume and the pressure in the fuel rail provide enough capacitance for consistent operations, but metering fuel when a large portion of the "open" time is dwell time can be tricky. This issue can be further compounded by the inertia in the fuel system. A dead head system (i.e. no return line) can have most of the fuel in the rail sitting near motionless in low fuel demand situations. The fuel pump must be able to accelerate that fuel inertia in the rail and fuel line quickly when an injector is opened. You will see some dead head systems with a diaphragm at the end of the fuel rail. It’s there to provide capacitance. Enough of my verbiage as that has little to do with what I’m asking here.

Yes, I suspect you would need to use the speed signal as the EFI system doesn't shut the fuel off if you were to just let out the clutch while idling. Without as system flow chart, it’s hard to know. Chuck35 seems like he may know something about the system logic, but is having issue with his computer.

 

[SnowmobileGuy]

Not sure where the edit button went. in the last sentence in my previous post I meant "ionbeam seems like he may know something about the system logic, but is having issue with his computer."

 

[SnowmobileGuy]

I did get a cahnce to try it this weekend. It woudl ahve been ncie to some sort of metric to it (e.g accelermonters tracking size and time of torque spikes), but I didn't ahve that capabilty in the garage, so I had to rely on the untrustowrthy butt-dyno. I tried advign the TPS to both 23 (on Diagnostic 1) and 20. I might have convinced myslef it was different, but after going back to spec (15-17), it wasn't different or at the very least I couldn't dicern any difference. So the guidance here is "don't bother".

 

[ionbeam]

I did get a cahnce to try it this weekend. It woudl ahve been ncie to some sort of metric to it (e.g accelermonters tracking size and time of torque spikes), but I didn't ahve that capabilty in the garage, so I had to rely on the untrustowrthy butt-dyno. I tried advign the TPS to both 23 (on Diagnostic 1) and 20. I might have convinced myslef it was different, but after going back to spec (15-17), it wasn't different or at the very least I couldn't dicern any difference. So the guidance here is "don't bother".

Ok, home again and not using a netbook on the road.

The ECU sets up a basic fuel injection shot and timing, then based on inputs from all the sensors trims the duration and timing of the fuel shot. The Gen I has a fuel pressure regulator and a fuel return system which lets the ECU calculate the fuel shot based on an expected fuel pressure. The Gen II does not have a pressure regulator or fuel return so the ECU has to compensate for the pressure spikes as part of the fuel shot calculation. When and how to apply the decel and accel is based on the status and rate of change from all the sensors.

Unlike many motorcycles Yamaha does not give us visibility to, or control over spark timing which plays a major role in how the engine performs.

After reading the following you will see that to prevent decel fuel cutoff you need to avoid completely closing the throttle. This can't be spoofed by adjusting the TPS because adjusting the TPS so that the ECU does not think the throttle plates are closed the ECU will continue to add fuel so there will be little deceleration. Plus, it is engine speed dependent and the table of engine speed is in the ECU software.

The TPS is powered by a +5 VDC reference voltage from the ECU and has a ground reference, also from the ECU also. The TPS is locked to the throttle shaft so that a 'wiper' moves along a resistor proportional to the movement of the throttle plates. The TPS returns a signal to the ECU such that idle will be ~ 0.650 volts and full open will be ~5.00 volts. The ECU does some math to convert the voltage to % of throttle. Thus 0.650 becomes 17% throttle open and 5.0 volts becomes 100% throttle open. The real trick is that the ECU follows how fast the throttle plates move and uses both the absolute position as well as the rate of change to alter the basic fuel shot.

The injection duration and the injection timing are controlled by the ECU. Signals that are input form the throttle position sensor, coolant temperature sensor, cylinder identification sensor, lean angle sensor, crankshaft position sensor, intake air pressure sensor, intake air temperature sensor, rear wheel sensor and O2 sensor enable the ECU to determine the injection duration. The injection timing is determined through the signals from the crankshaft position sensor. As a result, the volume of fuel that is required by the engine can be supplied at all times in accordance with driving conditions.

• Acceleration enrichment

Acceleration enrichment is provided in accordance with the signals from the throttle position sensor. As the rider operates the accelerator to accelerate the motorcycle from a constant speed, the throttle position sensor actuates in unison with the accelerator. The ECU interprets that acceleration has taken place through the throttle position sensor signal and executes acceleration enrichment. The enrichment volume is determined by the acceleration enrichment coefficient. The coefficient increases with the changes in the throttle position sensor, which also increases the actual enrichment volume. The enrichment volume is executed in accordance with the acceleration enrichment coefficient when the movement of the throttle position sensor has met the acceleration condition as defined by the ECU. Thereafter, the enrichment volume is regulated by the coefficient that changes in accordance with the damping rate. Note that the damping rate will have a direct role in surging and throttle responsiveness.

• Deceleration control

Deceleration control is effected in accordance with the signals from the throttle position sensor. As the rider operates the accelerator to decelerate the motorcycle that is in motion, the throttle position sensor acutates in unison with the accelerator. When the engine speed is greater than a prescribed value with the throttle fully closed (thus applying engine braking), the ECU executes a deceleration fuel cut-off. The injection of fuel to all the cylinders is stopped when fuel cut-off control is executed, thus improving fuel economy.

• Over-revving control

This function effects fuel cut-off control when the engine speed becomes greater than the prescribed value. The fuel cut-off control regulates the engine speed by stopping the injection of fuel into two cylinders when the engine speed becomes greater than the specified value. If the engine speed increases further, this control stops the injection of fuel to all the cylinders. Thus, the overrevving control effects fuel cut-off control in two stages.