Intermittent hesitation and just bad running.

I was on my way home yesterday. It was extremely hot out. Must have been 95 deg Farenhiet. High humidity just one heck of a hot sweaty day. Bike was runnig alright, then I stopped and got fuel. After that the bike just was idling rough and hesitating on accelleration. Even on the Freeway it would seem to cut out then pick up again, In slower traffic it would just drop down to a real slow idle quickly and just run bad. Seemed alright for about the last mile home, but has anyone else experienced similar problems? I hope it was just the High heat and cooler fuel but I have never experienced anything like this before and want to be sure it is not the start of some kind of problem.

 

I have experienced similar hesitation on my '02 vfr a few times in the past month. Last night I tried to do some diagnostics but no luck. I checked all the plugs and coils and they seem ok.

One thing I noticed when the bike is in neutral, I tried to climb up slowly and smoothly through the revs. On the way up I can get to about 2500, then it suddenly jumps up above 5000. Then trying to go down smoothly from 5000 it will go to about 4000 then drop right off to idle. Is this normal? Can someone else try this? I'm thinking maybe it's one cylinder not working at low rpm.

Let me know if you find out what the problem was.. I'll do the same.

 

My 05 has been doing the same thing...intermittent hesitation and stumbling like it's running out of gas. Over the past few months I've checked just about everything imaginable, and so far haven't come up with an answer. Tough to figure out a problem that is intermittent and not easily repeatable. You might try running half a can of Sea Foam or Chevron fuel injector cleaner in your next tank of gas and see if that helps dry out the fuel and perhaps also clean the injectors a tad.

BTW, the sudden jump in revs during a neutral rev-up test is normal for a stock unmodified VFR. I think it's because the factory fuel map is fairly lean below 5K or so, and what you are feeling around 2.5K is a well-known lean flat spot, and then as you increase the throttle position the ECU richens the fuel map which causes the sudden jump in revs. Many people on VFRD have found that going with a higher pressure fuel regulator helps reduce some of the low rpm lean flat spots, or instead you could go with a PCIII with a richer map and O2 eliminators (case in point: most Dynojets PCIII maps for the VTEC VFR really richen up the mixture between 5-20% throttle and from 2-6K rpms). Unfortunately, I have found that none of these $100-300 dollar fixes totally eliminate the low rpm problems...usually they just make them easier to live with.

 

Another good product is called BG44K. I used it in my Honda and VW cars every 10K miles or so, so I'm sure it's perfectly safe for motorcycles as well...just make sure you dilute to the proper ratio. BG44K can be tough to find though as it's typically not sold in parts stores, but I think if you call an import dealership such as Honda, Acura, VW, Nissan, etc they might have it. Also try privately owned repair shops for the same models.

 

Hey, guy's. Just getting back about my intermittent problem. went through that tank of gas and it was just fine. I was thinking it had something to do with my bike being so hot from sitting in the hot sun all day and then filling it with cool fuel and running it on the freeway immediately afterward. I imagine that the big difference in temperature might have contributed. Any way I have been throug a few tanks of fuel now and everything seems just fine. I am glad it seemed to correct itself. Thanks for all the input. I will try to get some of the fuel system products mentioned and run them through just for safe measure.

 

Hey guy's,

I have been having a similar problem too. I get a hesitation usually in lower gears revving up between 4000-5000 rpm. If i roll the throttle very gently vs punching it i can notice as if the bike is starving for fuel, but once its past 5k its fine. If I open up the throttle from a standstill it seems fine.

I will go through another tank of gas, perhaps thats the problem, I just got a full check up from the dealer (used bike inspection free for the dealerships 1st anniversary in there new location) and it gave me 2 thumbs up.

It has been hot and humid here in TX too, and I notice the temp guage running hot, the fan kicked on a few time at stop lights.

I just turned 7K miles on my 02, I havn't changed my air filter yet, though I have a K&N sitting in the garage for it. Could this be an issue, though its not actually due.

Any advice is appreciated - cause its bugging the crap out of me!

 

Gonna throw out a suggestion here.

Back in the 'day', my dad said his old car would lock up badly during very hot weather, called it vapor lock. Ice on the fuel lines and some time would fix the glitch.

I know these bikes are fuel injected and computer controlled, but wonder if it's still possible a vapor lock/venting problem could still happen.

 

6th Gen's have that lean surge between 4-5K....I know I have it. I hooked my O2's recently and that problem reared its ugly head. Didnt really enjoy even riding the bike so tonite I re-bypassed em with the resistors and the fault almost completely went away. The bike was fun to ride, just a hint of leanness and I cruised between 4-5K rpm to make sure the problem was cured somewhat.

 

The VFR should not be a victim of vapor lock as the fuel pressure from the electric pump is much higher than older cars which had mechanical pumps. I ain't saying it can't happen, but it is very unlikely.

Venting issues are a separate can of bait.


Rex