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

[Fred W]

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.

Although it is risky to disagree with the good Professor, I am going to do that this time.

Yes, adjusting the TPS to indicate some voltage above the normal idle one will result in the ECU commanding the injectors to squirt more fuel than what is normally used at idle (actually at all throttle positions and RPMs), but this will not result in a higher idle rpm speed, just a richer mixture, since the throttle butterflies will not be opened any more than usual. It takes more O2 to raise the engine rpms up, not just more fuel. In fact, more air alone (with no added fuel) will still raise idle RPMs as can be evidenced by what happens when you pull off a vacuum cap or open the air bypass screws more.

If you happened to also be running a Power Commander on the bike you could then command the ECU to send less fuel across the board and thereby undo that rich condition. But the ECU should still think that you are never on zero throttle during overrun, so would never cut fuel entirely. The result would be a much lessened engine braking during decel and a much smoother transition from throttle off to throttle on since the fuel never gets completely cut. Just like on a carburetted bike.

 

[ionbeam]

... the ECU should still think that you are never on zero throttle during overrun, so would never cut fuel entirely. The result would be a much lessened engine braking during decel and a much smoother transition from throttle off to throttle on since the fuel never gets completely cut. Just like on a carburetted bike.

Try it and let us know how that works for you. Given the calibration range in the FSM you would have to have >750 Ω so the ECU thinks the throttle isn't fully closed. How much more is unknown. You are right that offsetting the TPS would result in a rich mixture, similar to bumping the CO setting. Rich fuel settings create mild bogging that will be perceived as smoother operation.

Since the span of the TPS is fixed, offsetting the low end would mean that the ECU would never see the throttle plates 100% open.

 

[Fred W]

Sorry , I have to disagree again, Professor I.

Yes the span of the TPS is fixed, but by rotating the TPS in the direction that we are talking about you will be end up telling the ECU that you are WOT earlier than it actually is, not the opposite. Since the difference in flow between 95% open throttle and 100% open throttle is less than 5% of the total, this should result in an insignificant fueling difference

I have actually already tried this little trick on my Fuel Injected Suzuki V-strom 1000 (which exhibits the same fuel cut characteristic) to soften the off to on throttle jerkiness. On that bike it works and doesn't cause trouble at WOT, although I have not (yet) fully mitigated the slightly rich running of the bike and crappy fuel mileage it results in. I do have a PC3 on that bike too, so it should be do-able with the right equipment, time and money.

But I haven't played with it at all on the FJR yet. That's why I subscribed myself to this thread, with hopes the OP would forge that particular new ground, and so I could lazily observe his results from the sidelines.

 

[rocketman]

When you close off the throttles in deacceleration the intake manifold vacuum exceeds a certain value and the fuel injectors are turned off. I didn't messure it - it may be around 20". And you have noticed as I have, if you are still deaccelerating, when you crack open the throttle bodies again, asking for fuel, you get no fuel until the intake vacuum goes back down. I have have tried several tricks to fake out the intake pressure sensor with different vacuum relief valves and bleeds but never got it quite right. For one think it always tripped the check engine light. the best thing was the power commander 3 with wallys smoothness map. It's not perfect but it works good enough.

 

[Fred W]

When you close off the throttles in deacceleration the intake manifold vacuum exceeds a certain value and the fuel injectors are turned off. I didn't messure it - it may be around 20". And you have noticed as I have, if you are still deaccelerating, when you crack open the throttle bodies again, asking for fuel, you get no fuel until the intake vacuum goes back down.

Where did you get this information; that the vacuum level was the primary trigger for the Fuel Cut on trailing throttle?

I sort of doubt that it is the sole mechanism, as vacuum can still be very high and you get the injectors turned back on with just a relatively small opening of the throttle.

It may be a logical "and" function of high vacuum, zero position (or below a certain threshold) from the TPS and the engine rpm above XX value that triggers the fuel cut. Unfortunately the Service Manual's FI theory section doesn't go that in depth.

 

[Constant Mesh]

"The Gen II does not have a pressure regulator ..."

Apparently it does have a pressure regulator. It's located in the tank with the fuel pump. Unlike the Gen I the fuel pressure is not modulated by the manifold pressure.

From the service manual ---

"The pressure regulator maintains the fuel pressure that is applied to the fuel injector at only 324 kPa (3.24 kg/cm², 46.1 psi)."

That's a bit higher than the Gen I regulated pressure of 36 psig.

 

[gixxerjasen]

Just food for thought from Ivan's page. Specifically about the FZ1 but as you can see, it applies here as well. Also to note, he now modifies the ECU on the bike as an option and removing the fuel cut is achieved this way as well.

This bike has lazy throttle response, and also the typical abrupt on/off throttle transition problem that all of todays EFI bikes have.
This is due to "fuel cut".....

"Fuel cut" happens when you close the throttle anytime above 4500 rpm (on this bike), the fuel injectors will stop.....

Upon re-application of the throttle, there is a delay before the system will start back up and re-wet the intake tract and combustion chamber..... the rider feels this as a delay and jerky response from closed throttle.... especially while leaned over in a turn.

In addition to the response problem, there is also one loud bang from out the exhaust that is usually heard when re-applying the throttle, after you change the exhaust.

Under these conditions, throttle response is much less than precise.

I have designed the FCEtm (fuel cut eliminator - $195.00) for this bike, and as a result there is a marked difference as to how much better this bike responds under any riding condition.... and as the first dyno chart shows, more midrange power between 6000 & 9000 rpm.

The product will add as much as 10hp due to the sub-throttles opening at a faster rate as well as preventing the EFI system from shutting off under decel conditions.

Combined with proper fuel and ignition mapping, this bike is transformed from a precarious ride under aggressive riding conditions to a perfectly smooth and predictable ride under any riding condition.

This product will make a marked improvement in any year fuel injected Yamaha FZ-1 (2006 - 2013) because it eliminates the root cause of the abrupt throttle response - "Fuel Cut" and it also offers the advantage of a faster opening rate of the sub-throttles.... regardless of what the factory may have done to improve this model.

The fact is... as long as there is "fuel cut", the problem will remain.

(Fuel Cut is a federal emissions regulation requirement for all EFI vehicles sold in the USA since 1980...... NO VEHICLES ARE EXEMPT !!

 

[Fred W]

Good stuff. I'll have to go nose around on Ivan's web site a bit.