Intermittent fault, loss of power, acceleration error, gen 1

[Abdistiller88]

Hello Everyone, My name is Benjamin!

I'm new to the group/forum. I purchased my first 2005 FJR gen 1 back in 2020 from a motorcycle collector with very low mileage, 4,800 miles to be exact. I just hit 19,000 miles last week but, I've been having an intermittent fault in between the 14,200 miles that I've owned the bike and I really hope one of you may have experienced this same issue or may help guide me in the right direction.

After I purchased I replaced, all fluids, spark plugs, k&N air filter. I regularly service the motorcycle just to keep it running its best.
Everything on the motorcycle is original except for the slip on Staintune exhaust. I also had the TPS (Throttle Position Sensor) replaced due to an open recall that was never performed about 6 to 9 months ago from a local authorized dealer.

The bike idles perfectly at stop lights. The issue only occurs when I take it out on long trips. I live in FL and the weather gets hot.


The intermittent fault, loss of power I'm experiencing occurred way before I got my TPS replaced and continued after the updated TPS was installed. The issue doesn't occur right away but, it seems to be a regular occurrence when I ride long distance with the engine nice and warm. The motorcycle never throws a CEL (check engine light) or stores a fault code. My first experience happened when I rode with a friend to Daytona for bike week. The ride up there was fine but, the ride home was when I experienced the loss of power. I was cruising at 90 mph in the middle lane on I95. I changed into the left lane to pass someone, opened the throttle and the bike started acting up. My RPM dropped, Bike slowed down to 60 mph, exhaust popping or backfiring. I gave it full throttle got no response. If I slowly eased into the throttle the bike would respond but only allow me to accelerate to 85 - 90 mph until it would repeat the same symptoms. I decided to pull over and allow the bike to cool. After 20 to 30 minutes I got back on and rode home with no issues. The throttle was responding and I was able to accelerate from 90 mph to 130 mph no issues.

The issue happened again when I took a trip with friends and we went on a 4 day trip to Pensacola, FL. The ride there was perfect but, the ride home from Gainesville I experienced the same issues. So I did my research and I found out about the open recall and got my TPS replaced after the trip.

I've read that some previous owners experienced this same issue and after the TPS was replaced some reported they never experienced the symptoms while others had the throttle body assembly replaced and that corrected the issue.

I would greatly appreciate your advice. I love the bike and I'm not ready to give it up so quickly because of this one flaw

 

[RossKean]

TPS is certainly a possibility.
Before you do that, try opening the tank filler cap and see if the tank is under vacuum. Kinked vent hose or boogered up gas cap could be the problem.
Less likely but worth checking is the fuel pump.

Goid luck.

 

[torch]

It certainly sounds like it is not adding fuel when you open the throttle. If it happens again, I would immediately (after pulling over) put it in Diag mode and check the TPS values as you twist the throttle to verify smooth and consistent readings. While there, I would also verify that the intake air pressure and ambient air pressure sensors values make sense -- with the engine off, they should be darn near equal and at the current ambient pressure. The ECU looks at the difference to calculate the volume of air entering the engine.

So long as a sensor is within the defined acceptable range, the ECU will trust the values it provides and calculate the mixture accordingly. They have to be completely bonkers before the ECU throws a code, lights the light and drops into fail-safe mode.

While a plugged tank vent is certainly a possibility, I don't think your description fits the classic symptoms. A plugged vent issue is usually consistent and doesn't go away.

An overheated fuel pump is certainly possible -- the Gen 1 airflow famously heats the fuel tank, especially as fuel level drops. Google can produce any number of attempts to alleviate the issue. Perhaps two with the best feedback are "Chromeit's heat fix" combined with adding a gen 2 style heat shield under the tank using aluminized heat insulation from the local hardware store.

Another possibility is a sticking fuel pressure relief valve not responding to the drop in pressure as the throttle is opened. Which again could be caused by heat.

Good luck! Intermittent issues are particularly difficult too trace.

 

[Prosolar]

If its pop[ping might be loosing ignition, fuel still going through the engine but not getting burned... Check your spark plugs/wires and especially the resistors, look inside with a flashlight for arcing and check them for proper resistance... Most are in the 5k range but it will be fairly obvious if one is out.

 

[Bounce]

That sure sounds plausible. I could replicate it on my GL1500 with the kill switch. Hit it with a slight pause while underway (tunnels) and flip it back on. BAM! as that raw fuel (that had been flowing while off) lit off all at once in the pipes.

As for heat shielding: https://www.fjr-tips.org/mods/insul/insul.html

The example shows my first-pass with firewall "rock wool". It's now that aluminized "bubble wrap" heat shielding (lighter and weather/fuel resistent).