Base fuel pressure slowly drops while riding

GXR1147

GXR1147

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Start off with i did the initial turbo build about 2-3 years ago. RCC stage 1 on a gen 1 and it ran flawless. Couldn't be happier. Then I wanted more boost. Picked an used ultra plenum and and bought all he rest of the stuff new. Got it together over the winter (which ment relocating the FMU under the the throttle bodies and rerunning a lot of lines) and Frank tuned it about 6 weeks ago or something like that. Loaded it up and left powerhouse in the typical fashion, couldn't be happier then a pig in mud. Finally weather was good enough to take it for the first ride with he new set up. Pulled the bike out and let her warm up and we were off. First stop gas station a few miles away. Bike stalled twice at idle while leaving. And noticed the fuel pressure was down 1-2 lbs and the needle was a little shaky when it had always been rock steady. Kept riding, watching the AFR also and noticed it bouncing around (upwards in high 14's to 16's at time while at cruise speed/throttle position). Long story short, seemed like after we would stop somewhere and the bike would sit for a short while, the fuel pressure would get lower and lower each time when I would turn it back on. By the end of the day when I got it home it was down to 20 PSI. And could barely keep it running at idle or wouldn't idle at all. Pulled the tank and found a kinked return line and rerouted some things to make sure that issue was solved. Took the bike out the next day (yeasterday) and same thing. Pressure starts off fine, but as the day progresses it falls off. Tomorrow I'm going to run 12v to the pump directly and kick the return line to test the pump as suggested by frank.

Also worth noting, even when the pressure is down a little and I lean into it and start building boost, my AFR does still drop into the 11's like it should as long as the pressure hasn't gotten too low, one time it seemed to only get down into the 12's and I backed off real quick. The pressure gauge is in a location that is hard to see while riding so while the bike is starting to get into boost I can't (won't lean over to look) see what it's doing.

I figure the only 2 components that can cause this issue would be the FMU or the fuel pump itself. Just wondering if anyone else has seen this before. Thinking maybe the FMU doesn't like its new location and maybe heat soak could be a problem or the pump is just getting tired?
 
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I had a similar issue with a naturally aspirated bike, turned out the fuel filter was all clogged up. Replaced the filter and ran great. Pulling the entire pump can be a pain, though not hard, and I remember guys talk about drilling out the stock pump and put an inline filter to avoid the issue in the future.
 
I just replaced the file filter right before the second ride. Issue was still there. This pump is located behind the motor under the swingarm pivot. I installed it while the motor was out. I can imagine how fun it will be to replace if it is the cause of my problem. I'm also wondering if it's being affected by heat. So I'm gonna stop by my job and grab my heat gun. Hopefully find out in a couple hours when I get down to it. After dropping the kids off at school today
 
Thank, that's the route I'm taking. After all the testing I've done it seems like the most logical direction to take. I have a pump on the way from Richard as we speak. Supposed be here on Monday and I should have it on the bike Tuesday. Im going to finish replacing the rest of the fuel line that I haven't replaced yet as well.
 
It would have taken me much longer to figure mine out but I was data logging and at steady state cruise the A/F started spiking lean
 
I have an AFR gauge at the top of my dash and that's what it was doing. I also have a fuel pressure to confirm my suspicions. It started stalling easily leaving a gas station on the first ride after the tune. So I was on top of what it was doing wondering what was gonna be normal and what wasn't.
 
Mathewrussell52 said:
Check all your lines and fittings i had a similar issue and I believe I when the line got warm it leaked and the pump was sucking air.
Click to expand...
All the lines were just replaced except for the small section from the filter to the pump and the feed from the pump to the rail. I got all new Parker line that will be going in at the same time as the pump.
 
Yeah, it's the newer RCC one. I have a new fuel pump in it. Gotta finish the new fuel line tomorrow then I'll be able to test it out.
 
Lol, it didn't want to come out, it need some persuasion . I had to do it by myself and I used a jack on the center stand loop. Sketchy AF. So I had to resend the ears on the bracket back into place today when I changed out the pumps. My girl is gonna give me a hand tomorrow getting it back in and pluming the new lines.
 
No it wasn't. I try to get mine out every opportunity I can. Adulting limits that with work, kids and family stuff unfortunately. But I try to set an entire day aside and start out in the early hours of the morning and get lost on new roads until late in the evening.
 
Mathewrussell52 said:
Do you think it could be a gas tank vent issue???
Click to expand...
Na, pressure stays low even after opening tank to add fuel. I'm gonna start testing the charging system tomorrow and see if there's a voltage issue as things warm up. Only other thing left in the fuel system itself would be the FMU. I talked to Richard about it and there's isn't really anything in it to fail other then a diaphragm, and if it's not leaking it's good from what I was told. And they are too expensive to just throw one at it...
 
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