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FJR Motorcycle Forums
Technical & Mechanical Problems
Where the FI gremlins come from
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<blockquote data-quote="jestal" data-source="post: 243402" data-attributes="member: 477"><p>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.</p><p></p><p>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.</p><p></p><p>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.</p></blockquote><p></p>
[QUOTE="jestal, post: 243402, member: 477"] 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. [/QUOTE]
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FJR Motorcycle Forums
Technical & Mechanical Problems
Where the FI gremlins come from
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