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Discussion Starter · #1 ·
Right, so, now I've got an actual running issue with the bike.



Going down the highway, or just cruising around in general between 5 and 6,000rpm, I get a surge and loss of power. Inability to accelerate. Does not happen consistently, just comes and goes.

It has, on one occasion, happened above 6,000. But has not happened since.



No FI light. If I drop down to about 4,000rpm, it goes away, and I can accelerate back up where I want to be. During the surge, I have a real loss of power, no ability to rev the bike (full throttle might as well not exist) and The bike just generally acts like it's out of fuel or sputtering.



Ideas? I don't know enough about the engine/driveline to diag it without other knowledge. A quick google search has not yielded much (although perhaps I am searching the wrong things).
Any guess I have is a shot in the dark.
 

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I had a very similar problem with my car, and the problem was either an intake pressure sensor or a bad sparkplug cable; I'm not sure which one was causing the problem (probably both), but I do know they were both bad and were both replaced.
 

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Fuel filter more likely TPS depending on how many kms the bike has covered, the contacts may simply be worn out where you ride it most. Its likely the factory manual has a basic multimeter test for this.
 

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My guess is a +1 for throttle position sensor (TPS). That was scary stuff when I gave it throttle and nothing happened, twisted more and it sputtered (while losing speed...), downshifted because I was thinking I missed a gear, twisted again and nothing....then BAM! Instawheelie because the TPS "woke up" and saw that I 'wanted' near-full gas in 2nd.

Took it to the dealer the next day for those shenanigans.
 

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My first guess was TPS as well. I'd recommend testing it and making sure it is not the problem, because you're fucked when it shuffles off its mortal coil. I had one go out, and that bastard left me stranded at the bottom of a hill on a narrow bridge over a river. Talk about no good place to pull over and leave the bike…
 

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Mexican Hard Shell Taco
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My SV did just that when the TPS went bad. I could not just cruise at 4-5K rpms, it would hesitate and misfire but it would run smoothly if I went WOT.
 

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Discussion Starter · #7 ·
ran great for 400+km today. . .

I'll use my spare time to check the location and testing method for the tps this week. thanks for the suggested starting location guys.

should note: I've also had some hard starting issues in the last few weeks (I thought setting the valves would fix this, but no, it did not) and it's taking a rather long time to warm up lately. Temp is steady. fan doesn't kick in @ 100C, but I cannot recall exactly when it is supposed to either.

anyway, I'll check out the TPS asap. last thing I need is for this thing to quit on me when I am living so far from "home"
 

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Mexican Hard Shell Taco
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ran great for 400+km today. . .

I'll use my spare time to check the location and testing method for the tps this week. thanks for the suggested starting location guys.

should note: I've also had some hard starting issues in the last few weeks (I thought setting the valves would fix this, but no, it did not) and it's taking a rather long time to warm up lately. Temp is steady. fan doesn't kick in @ 100C, but I cannot recall exactly when it is supposed to either.

anyway, I'll check out the TPS asap. last thing I need is for this thing to quit on me when I am living so far from "home"
Hard cold starts are not an indicator of valve clearance issues, tight valves cause hard warm starts as they don't close properly. Hard cold starts are likely to be caused by sensor issues... Yes, my SV was a biatch to start cold...

But other sensors could be at fault here, don't know the "peculiarities" of the VFR FI, but some FI systems run in two different modes, speed/density at lower RPMs (where emissions are tested) and Alpha-N at high RPMs (not emissions and noise tested). For example, they will test noise at half the RPMs, they will shift at X% of the RPMs, etc. More information here:

Document Display | NSCEP | US EPA

That can make a bike run like crap at lower speeds, when it is running in speed/density mode and perfectly at WOT and/or high RPMs as it runs in alpha-n mode...

But lets keep it simple.

First of all, you adjusted the valves, but I can't recall you synchronizing the throttle bodies. When throttle bodies go out of sync you'll have a cylinder(s) that is(are) slacking while the others take the extra load. Whenever you touch the valves you should check the TB synchronization, in fact, in several bikes (for example, my Kawa Versys) require TB sync check much more often than the valves (TB sync every 7500 miles and valve clearance check every 26,500 miles).

Now back to the broken things, check the easiest things first. Make sure that you have no leaks in the intake, as in between the throttle bodies and the engine. Check for leaks between the MAP sensor and the throttle bodies. The rubber plugs that cover the vacuum "nipples" to sync the TB's also like to rot and leak. Any leak in there will cause the bike to run lean, and they are already dangerously lean from the factory, going any leaner makes them run like crap.

Then there are sensors, and they are easy to check. The easiest way to test a sensor is just to unplug it and test the bike. The ECU will know, instantly, as in turn the key on and get the FI light, that a sensor is out and it will go into limp mode. In limp mode the ECU will use values for that sensor that are stored in a "safe" map, those values are good to keep the engine running without blowing up. That method will work for the MAP, ambient pressure, IAT, O2 and engine temperature sensors. What are you looking for? Well, whenever you unplug the sensor that is giving funky values to the ECU the bike will run fine, not perfectly, but it will run good. The only sensor you can't test like that is the TPS, you'll need a good multimeter, which any self respecting DIY mechanic should have, to test it.


As a matter of fact, I rather troubleshoot an FI bike than a carbed bike. I've had nightmares where I'm pulling out the carburetors off my XJR1300... Then back in, just to find that I left a stupid o-ring out, and after the whole thing is repeated, the bike still doesn't run right.
 

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Discussion Starter · #9 ·
I have nothing but a basic toolkit where I am now. the 5th gen VFR runs. . .ohhh shit.. .I think it's closed loop mode at <25% throttle/steady rpm, and open loop at <25% throttle or varying rpm.

or those two terms could be switched. it's late. I dunno for sure.

the VFR uses a set of starter valves that replace a traditional choke setup (no idea if other FI bikes use em, Honda had some interesting and weird tech at one point). they basically bypass the throttle bodies and feed air directly into the intake chamber of each cylinder. they need to be synched or you'll naturally get a surge at idle (and mine does have a slight surge at idle. it's not much but it is there. they'll also cause my hard starting issue, and them plus the throttle set will cause the high idle.

So those gotta get done. although it isn't a hard service, but it does require some tool whoring on my part. oh well.

checking the R?R was suggested, although I don't know how that would impact the running condition of the bike. regardless, it's a common trouble spot so I'll have a look when I can. if nothing comes up, I'll start checking sensors.
 

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I have nothing but a basic toolkit where I am now. the 5th gen VFR runs. . .ohhh shit.. .I think it's closed loop mode at <25% throttle/steady rpm, and open loop at <25% throttle or varying rpm.

or those two terms could be switched. it's late. I dunno for sure.

the VFR uses a set of starter valves that replace a traditional choke setup (no idea if other FI bikes use em, Honda had some interesting and weird tech at one point). they basically bypass the throttle bodies and feed air directly into the intake chamber of each cylinder. they need to be synched or you'll naturally get a surge at idle (and mine does have a slight surge at idle. it's not much but it is there. they'll also cause my hard starting issue, and them plus the throttle set will cause the high idle.

So those gotta get done. although it isn't a hard service, but it does require some tool whoring on my part. oh well.

checking the R?R was suggested, although I don't know how that would impact the running condition of the bike. regardless, it's a common trouble spot so I'll have a look when I can. if nothing comes up, I'll start checking sensors.


I don't see how the R/R could be related to this type of behaviour at all. Unless you're just wanting to check it as a point of routine maintenance, I'd skip it.

I had a similar issue when a coil was going bad on a Trophy 1200. That said, it was a known weakness of that particular model, which made it easy to find similar problems on a Trophy-specific section of a Triumph forum.

TPS makes sense to me - to a point. My TPS experience mostly extends to the Jaguar fuel injection system, which uses it more like an accelerator pump, so that the system isn't behind the curve when you leave a stop. If it failed at 4,000 RPM I don't know how noticeable it would be.

Does your bike use TPS for fueling decisions, exclusively, or is there some kind of airflow sensor? I'm guessing I'm over-thinking it, and bringing non-relevant questions to the table. So, please feel free to disregard everything I've posted, except the point about the R/R. :lgh2
 

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It could be something as simple as water in your gas.
 

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Discussion Starter · #12 ·
Been through 2.5 tanks from 3 different stations. Doubtful.
 
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