Fuel Reserve

[Bones]

A couple of years ago heading to the annual Mapleton Muster I noticed the bike was down a little bit on power nearing the top of the range but wasn't too concerned as i had a passenger on and the bike still seemed to be running ok, so headed to the servo to top up on fuel for the days ride. As I was pulling in i noticed it started to run on three cylinders, gave it a couple of revs, same thing so assumed a spark plug must've packed it in but decided to check it out after breakfast. Asked a couple of people at the cafe if they had a plug spanner because that's the symptom it was giving.

After breakfast started it again and it got progressively worse running from three cylinders then two cylinders until it finally stopped. It was then I noticed the pump was clicking like mad and no matter how many times the key was turned on and off it just wouldn't build up pressure, so deemed it the culprit. Pulled the inlet hose off the pump and hooked it straight to the carbs and it fired straight up and ran like a train for the rest of the day.

I've been fiddling around with bikes and cars since I was a teenager so have a little knowledge on how things work and can trouble shoot some problems, but in this case what gave the impression to me it was spark related turned out being a fuel problem, so maybe that's what other people feel when riding and are thinking as well.

I can't see the reserve function being too complicated on the fuel pump models where the manufactures went to the extra effort to design it where it affects both spark and fuel. The early models got away with simple petcocks, why over complicate things with the pump models.

[FJ_Hooligan]

If it was simply a cutout for power to the fuel pump, it wouldn't need to go through the CPU. Just wire a power lead to the pump and move on. It goes through the CPU because it does more than simply restore 12v to the fuel pump. I believe it does both simultaneously - changes the duty cycle of the ignition to give the feeling of a miss, and reduces the fuel pressure so the pump doesn't force fuel when the timing is off.

Look at items P,Q & R on the diagram. They are all connected to a transformer with 12v supplied to the other side from the main switch. The CPU will modulate the current flow through each transformer (all four ignition coils for timing and the fuel pump relay for pressure), by varying the duty cycle of the waveform applied.

PS - An F-18 is 1990's technology. Now if you had said YF-22...  

The coils (U) and the fuel pump relay (T) are NOT digital devices.  They are not driven with TTL logic, and there is no transformer, they simply receive whatever voltage that the main switch provides.  The reason there is "duty cycle" for the coils is to control the charging dwell time.  Coils charge up very fast.  Keeping the current flowing after they reach maximum charge will overheat the coil and reduce its life.

The ignition CPU changes the coil duty cycle to reach maximum charge just before the crank position where the plug needs to be fired.  The CPU calculates the time to start charging the coil so it is ready when needed and attempts to avoid excess current flow through the coil.  The duty cycle is also varied to account for the switch voltage.  That's why the switch voltage is an input to the CPU.  The dwell time (duty cycle) varies based on how much voltage is being supplied to the coils.

I still find it hard to believe a bunch of engineers would design a complicated reserve function that interfered with the ignition and could possibly cause a fouled plug.

[Mike Ramos]

If it was simply a cutout for power to the fuel pump, it wouldn't need to go through the CPU. Just wire a power lead to the pump and move on. It goes through the CPU because it does more than simply restore 12v to the fuel pump. I believe it does both simultaneously - changes the duty cycle of the ignition to give the feeling of a miss, and reduces the fuel pressure so the pump doesn't force fuel when the timing is off.

Look at items P,Q & R on the diagram. They are all connected to a transformer with 12v supplied to the other side from the main switch. The CPU will modulate the current flow through each transformer (all four ignition coils for timing and the fuel pump relay for pressure), by varying the duty cycle of the waveform applied.

PS - An F-18 is 1990's technology. Now if you had said YF-22...  

The coils (U) and the fuel pump relay (T) are NOT digital devices.  They are not driven with TTL logic, and there is no transformer, they simply receive whatever voltage that the main switch provides.  The reason there is "duty cycle" for the coils is to control the charging dwell time.  Coils charge up very fast.  Keeping the current flowing after they reach maximum charge will overheat the coil and reduce its life.

The ignition CPU changes the coil duty cycle to reach maximum charge just before the crank position where the plug needs to be fired.  The CPU calculates the time to start charging the coil so it is ready when needed and attempts to avoid excess current flow through the coil.  The duty cycle is also varied to account for the switch voltage.  That's why the switch voltage is an input to the CPU.  The dwell time (duty cycle) varies based on how much voltage is being supplied to the coils.

I still find it hard to believe a bunch of engineers would design a complicated reserve function that interfered with the ignition and could possibly cause a fouled plug.

I still find hard to believe a bunch of [FJ Forum members would expend so much time and energy discussing] a complicated reserve function that interfered with the ignition and could possibly cause a fouled plug...!!! (...!!! added for emphasis)  

But then if the fuel pump shuts off before the plug(s) foul would it not then involve the CDI, uh CPU unit... so perhaps the real question is who needs F-18 or even YF-22 technology when we have FJ(H) technology...?

Smile gentlemen!

[FJmonkey]

Mine don't work. And frankly I really don't care to fix it. I am old school and track my miles on the trip meter. When I am low on fuel I know it by habit. I know what fuel starvation is when I had vapor lock issues with a plugged fill cap on my '86. When my '86 cut out due to the RESERVE function it was just that, lack of fuel till the reserve switch was cycled. I gave that up when I converted to the 84/85 petcock. My '89 has never shown low fuel or acted like it was low till bone dry. I know the light works.

However, I enjoy the banter after a long day at work. I imagine the campfire warm and hissing from the Thermite, the lies about how fast we were, the truth about how old our bikes (and our selves) are. Talk of tires and oil and the O' SHIT moments we have all had.  Mike said "Smile" and I take that as keep going and keep it friendly.

[Pat Conlon]

Discussion is good. Different points of view are good. Uncertainty is good. It's all good. Healthy.
With all the talented folks here, the truth will become evident.

I love this forum.

[FJ_Hooligan]

Respectfully, I present the following analysis of the Digital Ignition Control System diagram:

The first diagram shows inputs into the Digital Ignitor Unit (H) which contains some level of logic in the CPU/Microprocessor (O).  Three outputs are 2 Ignition Coil Driving Circuits (Q and R) and a Fuel Pump Driving Circuit (P). 
 
Starting from the upper right of the diagram, all power comes from the Main Switch (C).  This is 12 volts from the battery.

Dropping down to the bottom of the diagram this 12V directly feeds the coils and the fuel pump relay.  This would be the red/white wires that power the coils, there's no varying this voltage, it is whatever the battery is.

What I understand about ignition control and coils is as follows:

Current flowing through the coil primary circuit produces a field that induces (or creates) a voltage in the secondary winding.  When the current flow in the primary is interrupted, the secondary voltage discharges through the spark plug causing the spark. 

The secondary voltage has a threshold which must be achieved in order to create a spark.  Anything less than this threshold voltage will NOT produce a spark.  The primary coil circuit has a fixed resistance and pushing 12V through it determines how much current flows.  The amount of time the current flows is proportional to the charge induced in the secondary coil winding.  This is also known as ignition (or coil) Dwell Time.  The Rated Voltage Circuit (N) is an input to the calculated Dwell Time.  Higher voltage requires less Dwell Time.

The ignition controls when the plug fires by interrupting the ground side of the coil primary circuit.  When the ignition has the coil connected to ground, the coil is charging.  How long the coil is allowed to charge is the "Duty Cycle" or dwell time which determines how much charge the secondary coil circuit ultimately gets.  Once the coil has reached maximum charge, additional charging dwell time will result in overheating and reduced life of the coil.

Going through the notes on this diagram;

#1 Determining proper ignition timing.  The ignition must interrupt the primary coil circuit at the proper time to deliver the spark at the desired BTDC point.  This is the ignition timing curve which will vary based on known variables such as RPM and state of the pressure sensor (F) and it's input to the CPU the Vacuum Control Circuit (L) (which is indicative of the throttle position).  I do not know why there are 2 lines drawn between F and L, that would typically indicate that 2 signals are provided by the Pressure Sensor.  I assume the Vacuum Control Circuit takes the signal from the Pressure Sensor and converts it into a logic signal that the CPU can comprehend. So, based on the ignition curve solution for when the spark is supposed to happen, the ignition will cut the coil primary circuit ground based on knowing the position of the crank via the Pickup Coil (G) and the Wave-Shape Shaping Circuit (M).  The Wave Shaping circuit converts the analog sine-like signal produced by the Pickup Coil into a digital signal for the CPU.  Knowing RPM, desired ignition advance and crank position, the CPU can determine the appropriate point to cut the ground and fire the plug(s).  The CPU also calculates when to start charging the coil so it's ready for the spark event while avoiding overheating the coil.

#2 Sensing the engine revolution speed.  As described above, this is required for proper ignition timing.  The Pickup Coil signal is used to measure RPM for the CPU. 

#3 Determining timing for switching on ignition coil (duty control).  The CPU knowns when to fire the coil but it must also know when to reconnect the coil primary circuit to ground to "recharge" the coil.  Under nominal conditions, there is a known minimum charging time (duty cycle) to assure enough secondary voltage is produced to spark the plug.  Simple math in the CPU can solve for the crank position at which the coil circuit is turned on to get (at a minimum) threshold charging.  The coil only needs to be charged to its rated secondary voltage.  Additional dwell time will cause overheating.  The dwell time is also modified to compensate for the switch/battery voltage seen at the coil.

#4 Increasing ignition primary current for starting the engine.  This one kind of  bothers me because it says "current."  Up to this point I have maintained that the coil charging is a function of time given that fixed coil resistance and battery voltage produce a fixed current flow through the primary circuit.  The coil charge (and duty cycle) is also a function of the current flow.  For the ignition to have the ability to allow more current flow through the coils implies that the Ignition Coil Driving Circuits (Q and R) would have to have a varable series resistance that would allow more current to flow through the coil.  That it only does this for starting means that whether it is time of current flow or amount of current flow, the end result is it doesn't matter once the engine is running.  Maximizing voltage at the coil will produce more current flow and faster dwell time. 

#5 Sensing engine stall.  This has been explained.  If the engine dies, the CPU shuts off the fuel pump. Pickup coil provides this signal

#6 Preventing over-revolution of the engine.  Rev limiter!  Again, pickup coil derived signal.

Conclusions?  Based on this, I don't see how the ignition could cut out one coil without causing significant engine stumble.  The coil is either going to fire or it's not.  Even a degraded spark should ignite an air/fuel mixture.

The fuel level is monitored by the Fuel Sensor Input Circuit (I).  When the level gets low enough, the reserve function kicks in.  The Reserve Switch (D) and Reserve Switch Input Circuit (J) override the fuel pump relay cutoff and keep (or reapply) power to the pump.

The Fuel Pump Driving Circuit (P) is a ground path for the Fuel Pump Relay (T).  When grounded, the relay is activated and the pump runs.  If the Pickup Coil (G) and Wave-Shape Shaping Circuit (M) indicate that the engine is NOT running, then the fuel pump relay is activated for 5 seconds then shuts off.  This signal also provides the logic to shut the fuel pump relay off when the ignition is on but the engine dies (a wreck).

The Ignition Coil Driving Circuits (Q and R) control the grounding of the coil charging circuits and are only for dwell and ignition timing.

[Mark Olson]

Noel, 
no fuel pump to go bad , I have a larger hose to fill my bowls.....
larger needle and seat that don't plug up , and living in California my fuel is good.

So yeah ,, I'm Glad.

As for the Reserve switch quest , it appears the fuel relay power is cut ...and what else? maybe it reduces power to conserve fuel to get you to the next gas station. An off the road stationary test is invalid.

Please conduct the following test for the good of the FJ collective.
attach sensors and probes to your ignition system to record input and out put voltages while operating your FJ.
now ride till you run out of gas and have to switch to reserve but don't switch till the engine dies and you can record your readings ... Like does the engine still get spark when you have stalled with the reserve switch still off.
Make sure you ride to a remote area as roadside tests are dangerous ..

I am counting on you.

Yeah, sure Mark. as soon as I finish the parabolic algorithms for re entry I'm working on I'll move onto the serious stuff. 

Mark, I don't have a handle on your sense of humour and I don't want to offend you but I will go with my gut feel and assume your suggestions are tongue in cheek.

On the off chance you are being serious......

Why is an "off road stationary test" invalid. How does forward speed effect such a test?
You agree power is cut to the fuel pump. Why would you then have reduced spark as well if there is no fuel to ignite?

There is one point that many seem to overlook, it is just a fuel reserve function on a garden variety bike. Just how complicated were Yamaha going to make it?

I say again, there is no mistaking a bike running out of fuel with one running out of spark.

As for the bigger needle and seat (which really isn't that much bigger and the bigger hose which is irrelevent), they just let bigger crap through.
The benefit from the filter the pump allows you to run is less crap in your carbies. A fuel pump should only need replacing once in the entire life of your bike, hardly a biggy.

You are lucky to live somewhere with good fuel. We are also lucky here in that regard.



IMO

Noel

yes Noel , it is all in jest ..... I would think by now after all these years you would know when I am winding you up.   thanks for playing. 

[rlucas]

Respectfully, I present the following analysis of the Digital Ignition Control System diagram:

The first diagram shows inputs into the Digital Ignitor Unit (H) which contains some level of logic in the CPU/Microprocessor (O).  Three outputs are 2 Ignition Coil Driving Circuits (Q and R) and a Fuel Pump Driving Circuit (P)....

TL;DR

https://www.youtube.com/watch?v=fsOrty4RmSA

[FJ_Hooligan]

Rock,
Perhaps you've seen my other video:

https://www.youtube.com/watch?v=yefVpB5GEio

[ribbert]

I still find hard to believe a bunch of [FJ Forum members would expend so much time and energy discussing] .......
Smile gentlemen!

Mike, it is far better use of forum resources (and time and energy) than repeatedly launching unprovoked, long winded tirades denigrating fellow members wouldn't you say?

Noel

And yes, I'm smiling.

[Pat Conlon]

aaaaawh, just when I was feeling the love. 

Someone piss in your cornflakes Noel?

[Mike Ramos]

My goodness Noel,

Noel, it is just a little old reserve switch!

Deep breath & relax, repeat gently until the anger fades away or your until sanity returns...

Of course, pour a new bowl of cornflakes... unless the taste appeals to you!  :

Laugh Noel, it is the best medicine...

Noel, I think resort to additional comments via P.M. if you deem it necessary... 

As a reminder, this is not exclusively our Forum... let's at least let others enjoy it...

[Pat Conlon]

So, Hooli, if the TCI/DCI (aka CPU) calculates coil dwell time and adjusts the coil charging time according to voltage (among other factors) is the voltage is sensed at the CPU....or is the voltage sensed at the coil?
You could have 2 different values.... Voltage at the CPU could be different than charging voltage at the coil.

Coil relay mod vs Dwell times.  
Before my coil relay mod, I was seeing ~11.2 volts at the coil thru my oem wiring harness.
After the coil relay mod, I'm seeing a full 14.4 volts (Transpo VR mod) at the coils above 2k rpm.

That is a considerable increase in energy to the coils, which begs the question:
If the CPU is calculating the coil dwell time, based on current it sees at the CPU, so, with the relay mod. the coils are now seeing 23% more energy than the CPU sees.....
Are not the coils potentially subject to overcharging and possibly overheating?

I've had my coil relay mod for several years now, with no ill effects...even in super hot weather riding.

Cheers Hooli....Thanks for helping me understand....

[FJ_Hooligan]

Pat,
According to "theory" the voltage and the CPU and the coils needs to be the same to properly calculate coil dwell time.  As we know from the headlight relay mod, the actual voltage is a function of resistive wiring losses.  Without directly measuring the voltage at the coils and the CPU I don't know for sure.

Your ~11.2 volts for the OEM wiring, was that at idle or 2K RPM?  So we can compare apples to apples.

Looking at the wiring diagram it's kind of hard to decipher.  Looks like the Ignitor Unit get its voltage source directly from the main fuse box.  The coil power wire comes from the Relay unit.  It looks like the input power for the Relay unit is the Brown wire.  Following the brown wire shows that there are numerous branches off of this circuit.  It appears to power almost everything on the bike.

From this, I can only assume that the CPU voltage MAY be more direct and higher than the voltage showing up at the coils (direct measurement would confirm).  Maybe that's why the coil relay mod is so successful and doesn't harm the coils.  The CPU doesn't know the coils are at a lower voltage so the dwell time is shorter than it really needs to be.  Adding the relay gives the coils more voltage which would make up for the short dwell time.

All just a guess.  I would think a 23% increase in voltage would be significant.  Especially since I think there is a square somewhere in the math. 

[ZOA NOM]

If it was simply a cutout for power to the fuel pump, it wouldn't need to go through the CPU. Just wire a power lead to the pump and move on. It goes through the CPU because it does more than simply restore 12v to the fuel pump. I believe it does both simultaneously - changes the duty cycle of the ignition to give the feeling of a miss, and reduces the fuel pressure so the pump doesn't force fuel when the timing is off.

Look at items P,Q & R on the diagram. They are all connected to a transformer with 12v supplied to the other side from the main switch. The CPU will modulate the current flow through each transformer (all four ignition coils for timing and the fuel pump relay for pressure), by varying the duty cycle of the waveform applied.

PS - An F-18 is 1990's technology. Now if you had said YF-22...  

The coils (U) and the fuel pump relay (T) are NOT digital devices.  They are not driven with TTL logic, and there is no transformer, they simply receive whatever voltage that the main switch provides.  The reason there is "duty cycle" for the coils is to control the charging dwell time.  Coils charge up very fast.  Keeping the current flowing after they reach maximum charge will overheat the coil and reduce its life.

The ignition CPU changes the coil duty cycle to reach maximum charge just before the crank position where the plug needs to be fired.  The CPU calculates the time to start charging the coil so it is ready when needed and attempts to avoid excess current flow through the coil.  The duty cycle is also varied to account for the switch voltage.  That's why the switch voltage is an input to the CPU.  The dwell time (duty cycle) varies based on how much voltage is being supplied to the coils.

I still find it hard to believe a bunch of engineers would design a complicated reserve function that interfered with the ignition and could possibly cause a fouled plug.

Well, I didn't say they were digital devices, but the internal components of the CPU are, and the outputs to P,Q & R are not simply grounds. They are square waveforms that determine duty cycle by placing and removing the grounds to those devices. Also, the windings of the Fuel Pump Relay, and the Coils are indeed transformers, as you described above.

In any event, it remains a mystery, and mine has never worked as far as I know, and the bike runs fine.



edit: just found this on http://www.yamaha-tech.com/wiki/Yamaha_FJ1200

Electrical system
The FJ1200 features a standard 12 Volt electrical system. The alternator and starter motor are mounted behind the cylinders. Yamaha's self cancelling indicator unit is used and a variable resistance Level sensor is used to monitor engine oil contents with associated warning lights. A large fuel gauge is provided as is a low level warning light. Denso Capacitor discharge ignition is used in conjunction with two Ignition coil. The FJ1200 fuel reserve system used in later models is unusual in that when the fuel level reaches approximately 5 litres remaining ignition is cut to two cylinders giving the impression that the vehicle is running out of fuel, a reserve switch mounted in the fairing restores the cut cylinders allowing the rider to continue normally.[7][8]