2005 FJR Running Rich - Stumbling Mid RPM

[gbrmksmith]

My 2005 with 58,000 miles is running rich and stumbling a bit on acceleration (at least until the RPMs pick up). Anyone have/had this problem? Thinking maybe O2 sensor is not up-to-snuff and ECU is flooding the fuel air mixture.

Any help?

Thanks.

 

[kamal]

This is an old post but should still be relevant. Not sure if it will answer your question? https://www.fjrforum.com/forum/index.php?showtopic=114430

My '04 has never done this.

Good luck.

Al.

 

[Fred W]

My 2005 with 58,000 miles is running rich and stumbling a bit on acceleration (at least until the RPMs pick up). Anyone have/had this problem? Thinking maybe O2 sensor is not up-to-snuff and ECU is flooding the fuel air mixture.
Any help?

Thanks.

Not likely the O2 sensor as it only is looked at by the ECU at idle and steady cruise. But really easy to rule it out, just unplug it and the bike will run fine in open loop mode.

Much more likely that one of the other sensors (like temp?) is FUBAR. How does the bike run when cold vs when warmed up? Might want to go through the "Diag" screens (under the conditions when the problem is happening, whatever those are) and verify all of the sensors are in their expected normal ranges.

 

[gbrmksmith]

Thanks, I'll check.

 

[gbrmksmith]

Hinshaw's Honda in Auburn finally sorted this out. Turns out the fuel pressure regulator was malfunctioning and instead of diverting some of the fuel from the fuel pump back to the tank, was sending all the volume into the intake system causing the rich condition.

Replace the regulator and back to sweet running and proper mpg.

They stated that they had seen this on a few FJRs.

 

[ANZAC]

Good to hear you got it sorted out. There have been lots of these problems on both boards including my bike. I have a TPS on order but who knows for sure.

Need to find a good place to take mine in in the Portland/Vancouver area.

 

[Fred W]

Turns out the fuel pressure regulator was malfunctioning and instead of diverting some of the fuel from the fuel pump back to the tank, was sending all the volume into the intake system causing the rich condition.

Another way of saying that would be "The fuel pressure regulator wasn't regulating properly." On 1st gens the way the regulator works is to send excess pressure back to the tank.

FWIW 2nd gens have the regulators built into the fuel pump inside the tank. They do not have a 2nd fuel return hose.

 

[puppychow]

Hmmm. Is this fuel pressure regulator issue a pretty common issue which develops in relatively high-mileage FJRs? Mine at 72K on it and I have a "rich" running FJR also for the past few tankfuls. About 30-33 mpg or so.

I am about to pull the spark plugs to see how they look. I ran my finger through the outlet of the exhaust pipe and saw some carbon soot on my finger, but it was nothing bad really, but I don't know what good, or bad or worse carbon soot is that you can see in the pipes near the exhaust tip...so...

 

[Fred W]

There is a procedure in the FSM for measuring the pressure, but it requires enough gadgetry to make it a PITA. It's supposed to be 36 psi at idle with the vacuum hose disconnected. Then the pressure regulator is supposed to vary the fuel pressure based on manifold vacuum. As the vacuum pressure increases the fuel pressure is supposed to decrease. Maybe it isn't decreasing correctly from the base pressure?

You may want to inspect the vacuum tubing around the regulator, or use a MityVac and try sucking on the regulator and see if you have a leak.