Unsettling Throttle Behaviour

Hello, 

I have an ‘05 VFR800 VTEC ABS, ~43,000km on it. I’m having intermittent issues with the throttle and wondering if anyone has an idea of what is going on. Aside from this the bike is in great shape and runs/rides well. 
 

Basically it feels like I am fully closing the throttle and my hand position has not changed at all. This happens mainly when i’m cruising around taking it easy,  between 4000 - 6000rpm, on and off the throttle in traffic. The bike will lose revs/power, the nose will drop. If I don’t quickly apply more throttle, the bike will continue to lose revs, just like if I had closed the throttle and was coasting. Again, i have not moved the throttle position at all. It does this in rain or sun, hot or cold, any gear, any speed. It did it tonight on my ride home in a low speed corner and I had to quickly add throttle to keep the bike upright. 
 

I really love this bike but if I can’t trust it to maintain my inputs I really don’t want to ride it until this is sorted. Any help is greatly appreciated. I wonder if it’s related to the airbox flap activating?

Sounds like a Vtec transition or a TPS sensor issue. If you have checked the throttle cables & they are free moving & correctly adjusted = zero free play when bars are on the lock stop left/right which ever is the tighter side.  Then some of the Vtec guys can chime in, as the transition point was changed at various points in the model run. But IIRC this was the biggest complaint about the first Vtec model from 2002-2005 or 6. 

I don't believe the airbag flapper is the culprit. That rattling was obvious on both my 5th gen VFR800s, but never on my '09 Vtec (93K km).

Mohawk's suggestion of throttle cable fee play seems top of the list to check, and can be done in the garage. Start your bike and once the engine is idling normally, close the throttle then check how much you can rotate it before the engine speeds up. The book calls for 2-6 mm of free play. But if you do need to tighten it double check afterwords that engine speed doesn't change when your turn the handlebars lock to lock.

Do you know if your bike is completely stock and unmolested? In any case, you can also do a basic mechanical check to assess fuelling and electrical systems to affirm that everything's kosher.

Good luck

Questions and Suggestions......

- How fresh is your fuel? Could you have bad fuel, water condensation in the tank especially with Ethanol blended Fuel?

- Possible dirty Fuel Filter.

- What is the health status of your battery? How old is it? Are the terminals Clean and Tight?

- How old are the Spark Plugs?

- Check for a leaky/ruptured Fuel Pressure Regulator Diaphragm. Remove its vaccumm hose and check for any sign of fuel in the hose or dripping from the FPR hose connector, should normally be dry.

- When the fault occurs Does The Fi Light come On?

- Check Vacuum Hose to the MAP Sensor, make sure there are no kinks, cracks or breaks in the hose and that it is properly connected to the MAP Sensor.

- Suggest going through the process of reading the ECM memory historical fault codes, take note of any, then clear the memory. Go riding till the fault reoccurs recheck the ECM historical codes, an intermittent sensor failure might be logged in the ECM memory. A current active fault will have your Fi Light On while riding then displays the code once stopped and Sidestand is down, Ignition to On.

- Check the wiring and Fuse connector for Main Fuse B 30amp. This fuse feeds ALL your EFI stuff and commonly suffers from heat stressed wiring and high resistance fuse joints causing intermittent to total failure of your EFI.

- Check the Red 4P Connector at the Starter Relay. Make Sure the Red wire that come from Main Fuse A 30amp is Not heat stressed and has not melted the red plastic of the 4P connector, make sure the Red wire Spade connector is making good, clean, tight contact to the Starter Relay contact.

All of the above are some known causes of various forms of Surging and Bogging.

Assume you have the Service Manual? You can download it from this forum.

Good Luck.

Thanks Mohawk, Lorne & Grum for the detailed replies!

I didn't have much time this weekend but I checked the easy stuff:

- Fuel is "fresh", I've been going through a tank or two a week since late April. Latest fuel up was from Costco (in Ontario, Canada) for 91 on Friday morning. Before that was Shell 94 I think and the bike was running fine until I re-fuelled on Friday morning. It's somewhat difficult to get ethanol free fuel around me so most fuel I use is ethanol blended. I do put ethanol free fuel in for the winter

- Battery is new and sitting at ~14.3v at idle, terminals are clean and tight. This spring I replaced the stator, R/R (roadstercycle kit), and wiring and fuse holder/connector for both 30amp main fuses. No signs of heat damage since replacement. It was definitely cooked before replacement

- Throttle free play was at 0 - 1mm, I adjusted it to 3mm

- Spark plugs are new this spring

- The vacuum hose from the bottom of the MAP sensor looks ok as far as I can see it without removing the air box

- The FI light did not light up on Friday. I did see the FI light come on once a few weeks ago while riding, I pulled over and shut off the bike, started up again an all was ok

- I have the Haynes Manual and the downloaded manual, just trying to figure out how to read historical codes

- Looks like I'll need to pull the airbox to check the Fuel Pressure Regulator Diaphragm through the vacuum hose, I'll check this when I can

- This same bogging issue has happened sporadically throughout the riding season but it was particularly bad on Friday

- 'Mods': Delkevic slip on exhaust, K&N filter (cleaned/oil this spring)

Questions:

- Is there a way I can check for water in the tank?

- Should I siphon the fuel out of the tank and try new fuel?

I would try a new load of ethanol free fuel first. If the bike was running ok before the last fill, it seems to point to the fuel.

9 hours ago, lucwilride

Thanks Mohawk, Lorne & Grum for the detailed replies!

I didn't have much time this weekend but I checked the easy stuff:

- Fuel is "fresh", I've been going through a tank or two a week since late April. Latest fuel up was from Costco (in Ontario, Canada) for 91 on Friday morning. Before that was Shell 94 I think and the bike was running fine until I re-fuelled on Friday morning. It's somewhat difficult to get ethanol free fuel around me so most fuel I use is ethanol blended. I do put ethanol free fuel in for the winter

- Battery is new and sitting at ~14.3v at idle, terminals are clean and tight. This spring I replaced the stator, R/R (roadstercycle kit), and wiring and fuse holder/connector for both 30amp main fuses. No signs of heat damage since replacement. It was definitely cooked before replacement

- Throttle free play was at 0 - 1mm, I adjusted it to 3mm

- Spark plugs are new this spring

- The vacuum hose from the bottom of the MAP sensor looks ok as far as I can see it without removing the air box

- The FI light did not light up on Friday. I did see the FI light come on once a few weeks ago while riding, I pulled over and shut off the bike, started up again an all was ok

- I have the Haynes Manual and the downloaded manual, just trying to figure out how to read historical codes

- Looks like I'll need to pull the airbox to check the Fuel Pressure Regulator Diaphragm through the vacuum hose, I'll check this when I can

- This same bogging issue has happened sporadically throughout the riding season but it was particularly bad on Friday

- 'Mods': Delkevic slip on exhaust, K&N filter (cleaned/oil this spring)

Questions:

- Is there a way I can check for water in the tank?

- Should I siphon the fuel out of the tank and try new fuel?

Checking for water in the fuel is not a bad idea. I have had this happen before (I transferred fuel from another bike but there was some water in it as that bike's gas cap was leaky). 

See can you find something called "Wynn's Dry Fuel" or some sort of "water remover" which forces water to mix with the fuel and it burns off. Siphoning it might not work very well, you might leave some behind due to the shape of the tank.

However, as fuel floats on water, the water SHOULD be fully blocking fuel going into the pump or injectors so it shouldn't be running at all. 

How is the thermostat? I had a bad thermostat when I bought the bike in 2020 and it made it run extremely rough. The engine temp wouldn't budge above 55c when it should have been around 80c at "normal" temp. A new thermostat sorted that and it ran nicely after that. 

If I were you I'd go through @Grum's excellent list of issues first and then take a look at the above. 

Best of luck!

Thanks VFR78 & fabio222 for the replies. I'll be siphoning out the tank as best I can tonight and putting in new fuel with a water remover additive to try and make sure there is no water in there. I've found that since last year all the Ethanol free fuel options I had around have disappeared. There are new fuel regulations in Ontario as of last year and Ethanol free appears to be on it's way out here 😑. Edit: I forgot to mention, the thermostat seems fine, I tested it from cold start and the radiators only start warming up once the bike hits around 80 degrees C which I believe is what is expected.

Hello @Grum, I just checked the stored FI Fault codes. It is throwing code 22 = Faulty no. 3/4 Oxygen Sensor, no codes other than that one. Any thoughts on whether or not that could lead to the issue I am having?

I'll pull the fairings tonight so I can check the sensor, wiring and connector. Could someone explain how I can check the wiring between the sensor and ECM for shorts? It appears that I would check continuity of the black/orange wire between the ECM and connector? The other wire (that is not for the heating element) seems to be light grey in the wiring diagram and this connects to a green/orange wire that goes to most of the other sensors. Do I need to check that wire as well for shorts/continuity?

It looks like the heating element has it's own fault code (which has not been thrown) but I will check the resistance between the two white wires on the sensor itself anyway. This is a ~$300+ part for me so if there is anything I should verify prior to just buying a new one and replacing it I would appreciate any tips. Thank you!

Can I ride the bike with this faulty sensor or is it best to park it until that is fixed?

Hello All, 

I'm also interested in this conversation.

I have a 02 VFR Vtech... 63k kilometres in great condition. Up to December 23'

I have a big overhaul done, New cam chains and tensioners, plugs, filters, oil etc. Got her back, but couldn't ride due to crap weather for x6 weeks. I noticed straight away in 4th/5th gear a lag when climbing speed between 5/6k revs, then Vtech kicks in and it's fine !!

I've tried checking fuel etc, had it back to the garage and they changed the coils, but it's still the same.

Now they think it's the brand of plugs they used ? I've copied Grums solutions as I think electrics because it always lags at the same point and other than that, revs seem fine 🤔

But it is annoying and dangerous 😦

11 hours ago, lucwilride

Hello @Grum, I just checked the stored FI Fault codes. It is throwing code 22 = Faulty no. 3/4 Oxygen Sensor, no codes other than that one. Any thoughts on whether or not that could lead to the issue I am having?

I'll pull the fairings tonight so I can check the sensor, wiring and connector. Could someone explain how I can check the wiring between the sensor and ECM for shorts? It appears that I would check continuity of the black/orange wire between the ECM and connector? The other wire (that is not for the heating element) seems to be light grey in the wiring diagram and this connects to a green/orange wire that goes to most of the other sensors. Do I need to check that wire as well for shorts/continuity?

It looks like the heating element has it's own fault code (which has not been thrown) but I will check the resistance between the two white wires on the sensor itself anyway. This is a ~$300+ part for me so if there is anything I should verify prior to just buying a new one and replacing it I would appreciate any tips. Thank you!

Can I ride the bike with this faulty sensor or is it best to park it until that is fixed?

I wouldn't worry too much about the Code 22 for the O2 sensor at this stage, other than to perhaps check its 4P Black connector for good, clean connections. The Service Manual Symptoms for this Fault States - "Engine Operates Normally".

It would be highly unlikley the O2 sensor fault would cause your nasty issue as the O2 sensor just provides feedback info to the ECM (closed Loop Mode) for A/F ratio fine trimming.

Did you clear the code as suggested? You want to do this and re run your bike, who knows when that O2 Sensor DTC could have been logged to memory, if your bike gives you a hard time, its after that when you want to see and recall if any intermittent fault has been stored to memory. AND when riding when the fault occurs check the status of the Fi Light as quick as you can IF you can! A sudden flash of the Fi Light could also mean a momentary loss of EFI Power - The Black/White wire coming from the Engine Stop Relay and ultimately from Main Fuse B 30amp previously mentioned.

With the memory cleared any highly intermittent error detected by the ECM (there one second, gone the next) will be stored and may help in isolating a problem causer.

An intermittent sensor issue, such as the TPS, a Fuel Injector, Ignition Pulse or Cam Pulse Generator etc is more likely to cause sudden changes to the bikes operation, not an O2 Sensor, especially as you've stated that "It does this in rain or sun, hot or cold, any gear, any speed".

And, as mentioned, an Active current fault detected by the ECM will have your Fi Light ON while riding, then displays the flashing code once stationary with SidesStand Down. If the fault suddenly comes good the Active code dissappears and no flashing code will be seen, However it will be logged and stored in the historical memory for later recall.

There most definetly is No problems riding the bike just because of a historical memory DTC of 22 for the O2 Sensor. If it was currently Active your Fi Light would be telling you so, you don't have that situation.

Just curious - When you changed the Spark Plugs. What brand and part number were they?

Be interested in hearing how you get on after siphoning as much as you can from the tank and refill with fresh preferably non Ethanol blended fuel.

There are stories of Fuel Stations (high humidity regions of Texas is one area) that do not purge their storage tanks, this allows the continued build up of water in the tanks because of Ethanols hygroscopic nature, this can ultimately end up in the fuel tanks of customers, something to think about!

Thanks again for the detailed reply Grum 🙏. Glad to hear the O2 should not be a major issue, I'll clear the codes tonight and see what pops up over the coming rides. 

9 hours ago, Grum

And, as mentioned, an Active current fault detected by the ECM will have your Fi Light ON while riding, then displays the flashing code once stationary with SidesStand Down.

On this point, do I just come to a stop once I see the light come on, put the side stand down and it will start flashing the code number? Do I need to shut the bike off?

The spark plugs are OE parts from partzilla, NGK, P/N: 31912-MCW-003 (IMR9B-9H). I'll pull the coils and just make sure they are all still snug in there. From the information I could find it seemed like the IMR9B plugs were the right ones, as opposed to the IMR8B. 

I've put Sta-Bil 360 into the tank for now, I'll run it this week and see if any change. Also still planning to pull the air box and check the fuel regulator diaphragm and also double check the various fuses and connections noted above. 

43 minutes ago, lucwilride

Thanks again for the detailed reply Grum 🙏. Glad to hear the O2 should not be a major issue, I'll clear the codes tonight and see what pops up over the coming rides. 

On this point, do I just come to a stop once I see the light come on, put the side stand down and it will start flashing the code number? Do I need to shut the bike off?

The spark plugs are OE parts from partzilla, NGK, P/N: 31912-MCW-003 (IMR9B-9H). I'll pull the coils and just make sure they are all still snug in there. From the information I could find it seemed like the IMR9B plugs were the right ones, as opposed to the IMR8B. 

I've put Sta-Bil 360 into the tank for now, I'll run it this week and see if any change. Also still planning to pull the air box and check the fuel regulator diaphragm and also double check the various fuses and connections noted above. 

To be honest with the four VFR's I've owned I've never experienced an EFI fault while riding, so I'm going by what the Service Manual states. It's makes good sense that whilst riding and a fault is detected you don't want a distracting flashing light in front of you, only when stationary, sidestand down, kill switch to RUN, ignition to On that the code will display not sure if engine needs to be running, but the fault needs to be active.

Plugs are correct being the NGK IMR9B-9H. The optional 8B are a slightly hotter heat range plug.

Good luck with all the other checks. 

I wonder could we just be talking about dirty injectors?

If I had this issue with carbs I'd remove them and give them a thorough clean. I know that isn't as easy to do with injectors, and they don't tend to be as susceptible to gunking up, but it might be worth thinking about it. 

23 minutes ago, fabio222

I wonder could we just be talking about dirty injectors?

If I had this issue with carbs I'd remove them and give them a thorough clean. I know that isn't as easy to do with injectors, and they don't tend to be as susceptible to gunking up, but it might be worth thinking about it. 

Man I hope not, I'll rule out the other stuff first. For cleaning injectors is there actually an effective fuel additive that will clean them or would they have to be disassembled and cleaned? The bike does need a valve inspection this year so I could have a look at cleaning the injectors while I have the airbox and throttle assembly pulled out for that job

I'm lazy. To know that they were clean, you'd have to take them out. If you're out...clean them by taking them out. lol 

I've only used additives with some success. 

One track bike needs them to come out. It has for probably nearly a decade. 

If the bike runs fine everywhere except the vtec transition point, I'd be looking there. But if it only went wonk after the last refuel then switch out the fuel & see if it gets better. If mot then look further. 

BTW in my case, we changed the coils but the bike still had the same issue... Then, changed all the spark plugs and HEY PRESTO... That was it !

It runs perfectly now. NGK PLUGS went in, not sure the brand that came out 😕

Is there a VTEC solenoid valve which might be faulty? One which actuates the extra couple of valves in each cylinder at the VTEC transition point...