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Discussion Starter · #1 ·
I have an 03 R6 that is practically all stock; no aftermarket parts other than the back license plate assembly and the direction lights. It was running fine until recently and I would like some help to further troubleshoot. What's happening now is that I need to get the RPMs higher than before to accelerate and gain speed.

In neutral, it seems to idle fine and responds well when I open the throttle. When I put it into gear, it feels like it is dragging to get up to speed and it feels like it is about to stall if I don't get the RPMs up. In fact, I need to release the clutch at a higher RPM to really get going. At speed, the behavior isn't much different in that it feels like it dragging relative to the throttle.

Here's what I done so far:
  1. Removed all the ignition coils (look good) and tested. All in spec.
  2. Replaced the spark plugs
  3. Removed the TPS and tested. In spec. I've had it fail before and this feels different.
  4. Also, several weeks before the issue showed up, I changed the oil and filter with regular riding since.
I probably need to change the air filter but it looks fine and I have gone much longer without changing it with no noticeable performance issue like this. Looking through the forum, I saw some posts with close but not exactly the same issue indicating the fuel pressure regulator could be the culprit. The regulator, although I can see it, requires a lot of disassembly to remove because of the configuration so I really only want to mess with it as a last resort. I also found some opinions in the forum that these regulators don't generally go bad (and I am hoping that is the case).

I'd appreciate any thoughts on the problems and recommendations for next steps. Thanks!
 

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Fuel regulator is easy to understand.
377588

The THICK and clamped line entering from the bottom is from the fuel pump.
There should be another line that returns a metered amount (excess) fuel back to the tank.

The silicon line with the white stripe is a vacuum line.
Vacuum is highest at idle.
At idle, fuel demands are lowest.
So high vacuum causes the regulator to dump more fuel off the return line.

Fuel pressure regulators rarely have issue. But plugging and capping the vacuum line, which may close off flow to the return line, will allow you to read fuel pressure on the fuel pump.
 

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Discussion Starter · #3 ·
@Intuit Thanks for the response. So, you're saying that I can test it without taking it out? I'll need to figure out the tool to test but do you think the fuel pressure regulator could be what's causing the problem in my case if it has gone bad?
 

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Fuel pump is a suspect. I'm not saying it's the definite cause, but with the issue being as consistent as it is, both the regulator and pump are something that can be eliminated. In my prior car, engine miss at low-RPM and high engine load was the ignition (spark) breaking down. Might be able to use the rear brake to help load the engine on the stand. (though it's probably not going to be much competition for the engine)

You'll have to remove the line between the regulator and fuel pump and replace it with a temporary line that includes the fuel pressure gauge. I have no idea what the spec should be however.
 

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Discussion Starter · #6 ·
Alright, I'll have to plan testing all this out (tools, time, and space).
The dragging brake is not something that even crossed my mind. I imagine there'd be a burning smell but I won't discount anything. I really appreciate the input and will update when I make some progress.
 

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Discussion Starter · #7 ·
Update. I was getting set to start messing with the fuel pressure regulator when someone I was talking to said it's probably the coils. Since they weren't OEM, the specs aren't necessarily the same so I re-tested the coils and one was way off with higher secondary resistance. I don't know how I missed it the first time. I reached our the CoilSpec (the replacement brand) asking about the spec and realized one was practically dead. I got a replacement from CoilSpec and it fixed the problem. I also change the air filter and now the performance is back. So, lesson learned, check the coils thoroughly because loss of power is likely a coil. Thanks for all the help.

PS - The one Coilspec coil didn't last even close as long as to the OEM replacements from the recall but customer service was great and I would recommend. We'll see how durable they are in the long run.
 
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