GoneAce Posted January 14, 2023 Share Posted January 14, 2023 2003 vfr800 (6th gen). Known mods/maintenance- vfrness installed, new coils, new plugs, new fuel pressure regulator, exhaust baffles removed, air box flapper bypassed. Bike cold starts very rough, smells like it’s running rich, will bog/die with quick blips of throttle but if I roll into it it’ll rev all the way out. It smells like it’s running rich and smokes a small amount. Volts at battery read 13.5-14.5 at idle. I’m only getting about 8 volts at the coil harness plug and I’m assuming that’s the issue, where should I start to find out why I’m getting low volts at the coil? edit- error lights are 9,11,21,22 for iat sensor, speed sensor, and both o2 sensors Quote Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted January 14, 2023 Member Contributer Share Posted January 14, 2023 What is the state of Main Fuse B 30amp? Check this for an overheated discoloured fuse and wiring as it can suffer badly from high resistance joints and burn ups (see attached). Main Fuse B is the 12v supply via the Engine Stop Relay for ALL your EFI stuff on the Black/White wire, it also directly feeds the Ignition Coils, and, as you mentioned, you should be seeing Battery Voltage not 8v on this wire, most likely the cause of all your problems. The other weak link is the Blue 18P connector where this voltage goes to and from the Engine Stop Relay, high resistance joints can develop within the pins and sockets of the Blue connector. Trust you have the wiring diagram and Service Manual for your bike, they can be downloaded from this forum? For info - Make sure you have NO accessories or anything wired into Main Fuse B 30amp wiring as this power source is dedicated to the EFI system and should not be messed with. Once you've got the 12v restored on the Black/White wire clear all the old historical codes from the ECM, then start the bike and see what fault codes reappear, if any. Keep us posted with whatever you find. Good luck. Quote Link to comment Share on other sites More sharing options...
GoneAce Posted January 15, 2023 Author Share Posted January 15, 2023 16 hours ago, Grum said: What is the state of Main Fuse B 30amp? Check this for an overheated discoloured fuse and wiring as it can suffer badly from high resistance joints and burn ups (see attached). Main Fuse B is the 12v supply via the Engine Stop Relay for ALL your EFI stuff on the Black/White wire, it also directly feeds the Ignition Coils, and, as you mentioned, you should be seeing Battery Voltage not 8v on this wire, most likely the cause of all your problems. The other weak link is the Blue 18P connector where this voltage goes to and from the Engine Stop Relay, high resistance joints can develop within the pins and sockets of the Blue connector. Trust you have the wiring diagram and Service Manual for your bike, they can be downloaded from this forum? For info - Make sure you have NO accessories or anything wired into Main Fuse B 30amp wiring as this power source is dedicated to the EFI system and should not be messed with. Once you've got the 12v restored on the Black/White wire clear all the old historical codes from the ECM, then start the bike and see what fault codes reappear, if any. Keep us posted with whatever you find. Good luck. You are correct, the main 30amp vuse is darkened, I would assume that’s why the vfrness is installed, I replaced the fuse and it does not feel like it’s getting warm/hot anymore. (I bought the bike this way just recently, I’m just trying to get it back going). I have not checked that other plug yet, is there another way to address that 30amp fuse better? Will check that other plug today but thank you! Quote Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted January 15, 2023 Member Contributer Share Posted January 15, 2023 What does the fuse holder, wiring, and the inline joiner look like, anything like the picture above? You could purchase one of these from any good automotive store. (See attached) Solder and sleeve this into the existing wiring eliminating the inline joiner. Have you re-measured that 8v you had since replacing the fuse, has it increased? Suggest you clip your meter black lead to the battery Negative terminal, using your wiring diagram follow the Black/white wire back from where you measured 8v to the 18P Blue connector, probe the wire both sides of the connector see if one side has the 8v and the other 12v if so you've found the fault, if not then follow the wire up to the ESR Relay measure it both sides of the Relay. Keep doing this all the way back to the Main Fuse and ultimately the Positive battery terminal. Somewhere you should find where the Voltage drop is occurring. Perhaps you've already found the issue being the Main Fuse! Good luck. Quote Link to comment Share on other sites More sharing options...
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