DennisA Posted August 4, 2018 Share Posted August 4, 2018 I'm on my 5th VFR, the 3rd 5th gen and never had a problem until now. I purchased a low mileage 2001 with 22,000 KM, that had been sitting for a couple of years. A new battery, gas filter, air filter, synthetic oil and filter, spark plugs and new tires. The city driving operation is ok but highway riding with varying rpm suffers from bogging down occasionally but constant surges. It feels similar to 6th gen VFR. The surges may occur at 5,000, 6,000 or 7,000 rpm. I've tried Seafoam and Lucas engine cleaners. We exchanged the throttle body sensor. Should we have exchanged the entire throttle body? No error codes, idles fine. Valves not done yet.. Any suggestions would be appreciated, thanks, Dennis Link to comment Share on other sites More sharing options...
Member Contributer Cogswell Posted August 4, 2018 Member Contributer Share Posted August 4, 2018 Maybe a part of the puzzle is the phrase " . . . that had been sitting for a couple of years". It sounds as though you've made attempts at addressing varnish or gumming up of the fuel system with SeaFoam and other fuel additives. If the injectors are not operating properly the ECU has no way of knowing that - it's sending pre-calibrated amounts of pulse time to the injectors presuming that the appropriate amount of fuel is being delivered based on the presumed fuel pressure. On my 6th gen I have a Power Commander and tried many of the same treatments to overcome surging and stumbling - SeaFoam, etc. It wasn't until I removed the injectors and sent them out for a bench flow test and cleaning did I discover my issue. The spray patterns were decent at best - even after all the fuel additives. Once they were re-installed I had the ah-ha moment - it suddenly ran as smoothly as my 4th gen had. Granted, removing injectors on a 5th gen is not as easy as on a 6th - and I'm not saying this is the issue. But after nearly 20 years and a couple of years of sitting, a proper cleaning would be good maintenance even if it's not the root cause. You can try RC Engineering, or other services - they run about $100 for a set of 4. YMMV Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted August 4, 2018 Member Contributer Share Posted August 4, 2018 Hi Dennis. Agree with Cogswell here especially given the bike age. Very long periods of no riding isn't the best for the fuel system. Another thing that might cause your issues is the Fuel Pressure Regulator, and just like the flow rates etc of the Injectors it's not monitored by the ECU, so no fault code for it. Also have a very good look at ALL vacuum hose for any leakage. When you say you "exchanged the Throttle Body Sensor" are you referring to the MAP Sensor? Bit severe at this stage to be thinking of exchanging the entire Throttle Bodies! Just a thought! Good Luck. Link to comment Share on other sites More sharing options...
DennisA Posted August 5, 2018 Author Share Posted August 5, 2018 Thanks guys for the assistance, I'll let you know how I make out. Fuel Injector cleaning to start. Link to comment Share on other sites More sharing options...
Member Contributer KevCarver Posted August 27, 2018 Member Contributer Share Posted August 27, 2018 On 8/4/2018 at 11:57 PM, DennisA said: Thanks guys for the assistance, I'll let you know how I make out. Fuel Injector cleaning to start. Any progress? Link to comment Share on other sites More sharing options...
Member Contributer adkfinn Posted August 27, 2018 Member Contributer Share Posted August 27, 2018 On 8/3/2018 at 11:24 PM, Grum said: Hi Dennis. Agree with Cogswell here especially given the bike age. Very long periods of no riding isn't the best for the fuel system. Another thing that might cause your issues is the Fuel Pressure Regulator, and just like the flow rates etc of the Injectors it's not monitored by the ECU, so no fault code for it. Also have a very good look at ALL vacuum hose for any leakage. When you say you "exchanged the Throttle Body Sensor" are you referring to the MAP Sensor? Bit severe at this stage to be thinking of exchanging the entire Throttle Bodies! Just a thought! Good Luck. Regarding the FPR - from what I understand about these bikes it limits flow more than anything, since the fuel pump pushes more pressure than necessary. That said, when the FPR fails the bike will over-fuel since the FPR is allowing greater flow to the injector (even though the pulse/duration is still correct). Indicators that your FPR is failing would be running rich (which could make the bike run a bit cooler than normal), sooty/fouled spark plugs, and gas in your oil (which might be visible as a slightly rising oil level). Any of these are pretty easy to check. Also, how does the inside of tank look? Is it rusty and crusty? If it is crappy in the tank, it is possible that the fuel filter is clogged and is restricting fuel flow. It is easy enough to pull the tank and replace the filter (get a new tank gasket if you do this). Cheap and less work than pulling the injectors. If you do pull the injectors to have them cleaned and flow tested, you might as well clean the throttle bodies while you have them off, clean the engine v, and then replace all the vacuum lines, the thermostat, and the cooling joint o-rings at a minimum while you are in there. You might also consider the PAIR mod, replacing the old cooling hoses completely (why not pull the rads and complete a full cooling system flush since you've gone this far), and replacing the intake boots since they'll be all hardened up by now also.... It is a rabbit hole for sure, but you either need to enjoy a bit of wrenching or have a bunch of money to spend on labor if you are going to keep and properly maintain old motorcycles. Link to comment Share on other sites More sharing options...
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