Where the FI gremlins come from

Yamaha FJR Motorcycle Forum

Help Support Yamaha FJR Motorcycle Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

DonRed7

Well-known member
Joined
Dec 31, 2006
Messages
286
Reaction score
3
Location
P.E Canada
With my crayons and scrap paper.....

Quite simply,... The fuel rail is dead ended (isn't it?) instead of looped. And also of a smaller diameter than it SHOULD be so that...... The injector pulsing creates pressure waves in the rail and changes fuel pressures in an unbalanced manner in der tube affecting the injectors ability to deliver on a smooth curve along the rev range. Hence and Why the #1 cylinder is always the "leanest factory"=least wave affected. And why the #4 is always the "richest"=most affected..

:wacko:

No... Eh.... Oh well.

-Don

 
With my crayons and scrap paper.....
Quite simply,... The fuel rail is dead ended (isn't it?) instead of looped. And also of a smaller diameter than it SHOULD be so that...... The injector pulsing creates pressure waves in the rail and changes fuel pressures in an unbalanced manner in der tube affecting the injectors ability to deliver on a smooth curve along the rev range. Hence and Why the #1 cylinder is always the "leanest factory"=least wave affected. And why the #4 is always the "richest"=most affected..

:wacko:

No... Eh.... Oh well.

-Don

What you are supposing is true. Called the "water hammer" effect....like when you close the facet suddenly and you hear the pressure spike in the water pipe "hammer." Always an issue with a non-return type fuel rail. So much of an issue it is one reason why return-less port fuel injection systems are just starting to show up on production engines. So much of an issue you can bet your bottom dollar that Yamaha knows about it, too, and has compensated for it in the fuel injection calibration.

The problem with the theory you propose is that it oversimplifies the problem in proposing a reaction. And would it never simply manifest itself as one of the positions or injectors always being richer..or leaner...than the other. As each injector closes it creates a pressure spike (or water hammer) in the fuel rail that bounces back and forth thru the rail. An extremely fast pressure transducer in the rail would show a sinusoidal pressure change at any given point along the rail. Since there are four injectors there are four different pressure spikes bouncing back and forth across the rail from each injector closing. If another injector happens to open or be open just as a high pressure spike were to occur from an injector closing it would cause that injector to deliver rich, or vice versa if a lean spike happened along. Since any injector closing can affect any other injector up and down the rail it gets complicated. The second problem with the theory is that the nodes of the pressure spikes are always changing in frequency with RPM. At one RPM a node of a negative pressure spike might coincide with a particular injector. At a different RPM a node of a positive pressure spike might ovelay that injector opening. The water hammer effect can/could cause any given injector to go rich at one RPM and lean at another RPM.

All this is measured by the fuel injection system development team and software in the ECM compensates for it. Each injector would typically have a lookup table for water hammer effect compensation that is calibrated for each load and speed/RPM point to "tweak" the injector pulse width calculated to compensate for the water hammer effect.

This is also why there is generally a pressure accumulator on the fuel rail to dampen the pressure spikes caused by the water hammer effect in a return-less fuel injection rail. I don't know specifically if the 07 FJR has that or not but I would bet it does. It would look like a small can mounted on the fuel rail, looking much like the pressure regulator in the return style systems.

Sooo....it is true that returnless fuel injection rails do have a water hammer effect going on that does affect the fuel delivery from any given injection depending on the engine speed and load (injector pulse width.) However, suppossing that this phenomenon causes one end of the engine to always run lean and the other end to run rich all the time is highly highly unlikely. I would bet on this partly because I suspect Yamaha is compensating for the phenomenon in the ECM operation and partly the effect is way to random and rare and RPM specific accidently stackup so as to make one end lean all the time and the other end rich all the time. One of those "could happen" sorts of things but highly unlikely in the real world.

You realize that the 03/04/05 FJRs are return style systems and the 06/07 changed to the returnless system...??

There have been cases in the field where a company put a returnless fuel injection system on an engine and suffered some serious failures due to their lack of understanding of the water hammer effect and lack of appropriate compensation. In one specific case I recall in a marine engine the water hammer effect would cause lean related failures in one cylinder if the engine were operated at one load/speed point continously (like you do when towing a skier) and rich related problems in another cylinder at another operating condition (like towing a wake boarder). The guys that did the marine conversion switched to a returnless system due to coast Guard requirements regarding fuel return systems and did not appreciate the potential effect of the water hammer phenomenon.

Return-less fuel injection systems have several "positives" associated with them. Less heating of the fuel in the tank since the system is not circulating the fuel thru the (hot) fuel rail and then returning it to the tank. Less fuel vapor formed as a result and less strain on the evaporative emissions system. Less costly due to eliminating the return line and some fittings. Less leak potentials as the low pressure side is eliminated with all the plumbing assciated with it.

As far as the proposal that the fuel rail is is of a smaller diameter than it should be....???.....what makes you think that or leads one to that conclusion. The orfice in the injectors are tiny and only one injector is open at a time so the fuel rail is highly unlikely to become a fuel flow restriction even if all the injectors were stuck open 100% of the time. Nothing I can see about the fuel rail would support the idea that it is "of a smaller diameter than it should be."

 
This is also why there is generally a pressure accumulator on the fuel rail to dampen the pressure spikes caused by the water hammer effect in a return-less fuel injection rail. I don't know specifically if the 07 FJR has that or not but I would bet it does. It would look like a small can mounted on the fuel rail, looking much like the pressure regulator in the return style systems.
You realize that the 03/04/05 FJRs are return style systems and the 06/07 changed to the returnless system...??

As far as the proposal that the fuel rail is is of a smaller diameter than it should be....???.....what makes you think that or leads one to that conclusion. The orfice in the injectors are tiny and only one injector is open at a time so the fuel rail is highly unlikely to become a fuel flow restriction even if all the injectors were stuck open 100% of the time. Nothing I can see about the fuel rail would support the idea that it is "of a smaller diameter than it should be."
Thanks for the reply Jestal to my mid-sunday, afternoon, slightly beer induced mind fart. I work at a shellfish processing and have seen water hammer blow up a 6" shc 80 PVC "T" sending shrapnel through the metal ceiling.....

-The rail being smaller than it should be,... I was just embelishing a bit :unsure:

-06/07 's have the returnless and not previous yrs,.....Hmmmm interesting...

-Note to self.....*Check for accumulator*

Cheers

-Don

 
Last edited by a moderator:
Jestal, you can see the pressure accumulator/buffer chamber on the fuel rail in the 21st photo of the following thread:

https://www.fjrforum.com/forum//index.php?showtopic=18322

The accumulator is located between injectors 3 & 4. It's facing forward toward the head cover. The photographer's pen/pointer is just in front of the accumulator.

It appears to be crimped on a nozzle on the fuel rail. It also appears to possibly have an adjustment screw.

 
HogWash... The fuel rail has a pulsation dampner fixed to one end just for this reason. Also, if you install a fuel pressure gauge and run the bike, the needle stays extremely steady. Just my 2 cents.

 
Last edited by a moderator:
HogWash... The fuel rail has a pulsation dampner fixed to one end just for this reason. Also, if you install a fuel pressure gauge and run the bike, the needle stays extremely steady. Just my 2 cents.
Yes,.... we have realized that it has a dampener/accumulator.

-However,.... and this is an interesting point (And I have absolutely NO engineering background)...A simple fuel pressure guage could NEVER detect the pressure spikes that i am refering to within the rail even if they became extreme by engine design people, Why,... because,. they are 1/10 or 1/100's of a second events. So don't HogWash it.

Annnnd,... when i opened the topic with the crayons n' scrap paper thing in the first line. This was an attemp to keep it light and hope it dissapear quickly yet let people think a bit

cheers

-Don

 
Last edited by a moderator:
That would be the pulse damper. I thought I remembered seeing one on the 06/07 in some of the earlier posts/pictures but wasn't sure. I would be very surprised to see a returnless system without one. It has a plastic bladder inside with air pressure in the bladder to absorb the pulsations....we call it a whoppee cushion.....

Hogwash.....???..... :huh: :huh: :huh: Indeed, the pressure "pulsations" or spikes are so brief in terms of time that no mechanical gauge in the world could track them. You need a very sensitive pressure transducer and a 'scope at the very least. Even if a gauge could track the pulses your eyes couldn't see the needle moving that fast. But, you are right, run the bike and the fuel pressure will stay perfectly constant...that is how a returnless system works as opposed to the fuel pressure changing constantly with load on the engine like the return systems did.

The presence of the pulse damper indicates that the problem with the water hammer was at least considered and corrective action taken. If the damper is working and is in the correct location it should take out much of the pressure pulsations from the water hammer effect of the injectors closing but there will still be some effect cylinder-to-cylinder that the ECM will take care of via electronic compensation of the pulse width.

 
The "GURU" has spoken. :)

Once again, more info than the average person needs to know...unless you are personally tearing your bike down or a mechanic.

I hope I never have to be forced to work with any of this. :blink:

I believed the FJR to be a well built, quality machine and for the most part a trouble free unit. For me and all of you out there, I hope it stays that way. I would rather have the opportunities to ride than to have my bike in the shop. :rolleyes:

 
Why do you think this "water hammer effect" is limited to the FJR? Almost all of the FI bikes produced by the big 4 recently have a returnless system, just like the FJR.

 
Water hammer as in plumbing nothing more than a little air induced in the system.
weekend rider

Nonsense. Water hammer is caused by the LACK of an air chamber in the system. Water hammer is the sudden pressure spike when the facet is closed abrubtly. Putting an air chamber into the system to act as a cushion will prevent water hammer, not cause it.

 
Someone needs to tell the US Navy about waterhammers. Can't tell you the hours I spent awake trying to ignore the friggin' waterhammers that were alive all over the boat!! Yeah, I know they're "ships," Marines call 'em boats cause sailors hate it!! Semper Fi (the Fi is short for Fidelis not Fuel Injection :dirol: ).

 
Why do you think this "water hammer effect" is limited to the FJR? Almost all of the FI bikes produced by the big 4 recently have a returnless system, just like the FJR.


I don't know about the other folks but I personally expect all returnless systems to have the water hammer effect from the various injectors opening and closing. All returnless systems have to deal with the exact same hydraulic problems whether they are motorcycle, automotive or whatever. The situation is there on all the other bikes. Just some of the OEM's do a better job of coping with it than others. Whether it is the number of cylinders, pressure accumulator(s) added to the system or whatever, they deal with it.

Also realize that the "water hammer" pressure pulsations or spikes from the other injectors opening and closing may not manifest itself as a problem at all. The phenomenon is there it just doesn't create a problem on some arrangements. As mentioned, the pressure spikes travel thru the rail and the nodes of the pressure spikes might or might not stack on top of an injector location at any given RPM. At one RPM they might have no affect on a cylinder, at another RPM it might make that cylinder rich and at another RPM it might make that cylinder lean. No way of telling without doing some development work.

The problem might be more pronounced in an engine like the FJR where there is a single, compact fuel rail with no elastomeric connections (solid metal construction) and with injectors close side-by-side. Excellent opportunity for a pressure spike to resonate up and down the rail with plenty of targets to affect.

 
The "GURU" has spoken.
Once again, more info than the average person needs to know...unless you are personally tearing your bike down or a mechanic.

I hope I never have to be forced to work with any of this.

You won't have to Reggie- You have an 05. I love this geek stuff!

 
Top