[cornerhungry]

I Was out for a ride the other day heading up the hill. The bike ran fine minutes before then suddenly wouldn't rev past about 4k rpm. The maxx PRM can very but never past 5 or 6k. if I roll the throttle to full it bogs the motor and nearly dies out with a couple of pops out of the throttle bodies. I recently replaced the fuel filter but replaced another to be sure.
I'm leaning toward an electrical issue but my haynes manual isn't much help. Any one have any thoughts or ideas on how to better trouble shoot the electrical systems in our bikes. I Have a 2002 748. The Haynes manual doesn't even have a wiring diagram for my model. I also tried swapping the relays under the seat but same result.
Now I'm Scratching my head

 

[mlukason]

I had a similar experience with my ST3. It was running great. Then periodically it would loose power/bog down at about 6,000 rpm. I tinkered with many systems. Then, after exhausting any and all avenues I could think of at the time, I gave up and brought the bike to a dealer. They tested, tested and tested some more. Turns out the ECU was failing. It would intermittently enrich the mixture to the point it would just bog down.

My suggestion, before you spend lots of money, see if you can borrow an ECU and see if that takes care of the issue.

 

[jsheerin]

I had a similar thing and it turned out to be o-rings of the wrong material swelling inside the fuel line quick disconnects and blocking flow to the injectors. Ran fine at lower rpm, but I think mine would stop revving around 7k rpm when riding. I also had a similar problem but intermittently. That one resolved after running injector cleaner through the bike for a while. That was right after I bought it, and I think it had been sitting for a while.

 

[SS904]

Sounds like fuel starvation. I'd have said split fuel line if you hadn't mentioned being in there twice for the filter.

You replaced the filter, but did you check the sump and sump screen for gunk? Fuel pressure check? Clogged sump screen or failing fuel pump are both good possibilities. Easier to eliminate those items than digging into the electronics right away. Certainly could be the ECU, chip or something associated but I'd at least eliminate the obvious stuff first if you haven't already.

 

[xracer]

Could also be the crank angle sensor. Unlike but I’ve seen it happen, just won’t rev past 4000. Changed it and off it went.

 

[SlowDuck]

I had a similar issue pop up about 4 years ago (at ECM of all places) on my 2001 748. Engine shut down every time it was rev'd, but fired right back up. Turned out, as SS904 mentioned, it was a split fuel line. It worked fine until pressurized too much I guess. While it sucks replacing that fuel pump o-ring every time, I'd agree it's probably easier to check off the basics first.

Good luck with it.

 

[Heisenberg]

Above posters have provided good stuff to check

Crank Position Sensor
ECU
Fuel Pump Assembly plumbing


My 998 wouldn't go past 5k or so without engine braking and trying to throw me off the bike. One thing I did that helped a lot was a remove a power commander on my bike. Also had the tube from my pump to filter come loose which eventually caused my bike not to start due to lack of fuel pressure.

 

[Strega]

Suspect dirty air filter.

 

[cornerhungry]

Great suggestions. As soon as I get some time off I'll dig a bit deeper. I didn't mention that the tank is new to the bike. So I've recently replaced all internal fuel lines and moved the fuel filter to where the charcoal canister used to live between the throttle bodies. All fuel lines are rated for submersion. Before reinstalling the new tank I pulled the pump assembly and cleaned all the internal filters. Although it had been running great I had just topped of half a tank of fuel. .... so possibilities maybe but I had a thought if I pinch the fuel line before the injectors it should create a similar reaction right ? Didn't happen bike sputtered and stalled. So for now I'm ruling out fuel related. A couple years back I replaced the timing sensor perhaps I should double check the shim distance on it. There must be a way to meter the timing sensor at the Ecu to check its operation. Or check the voltage of the coils at the ecu to check values on them. Ecu's aren't cheap so I'm hoping to determine what it is without having to order a bunch of parts. Also I tried another chip and had same result.

 

[davy.j]

I had timing sensor problem, the bike would cut dead for a few seconds and then before it slowed down much would fire again then do it all over again.

Cure was to shim the crank sensor to just a few thou so it clears the gear cold (the gap grows as the motor warms and that's why mine would cut out)
I tried a different sensor but the issue remained the same... reduce the gap and the bike runs perfect right up to the limiter.
Shims are easy to make out of blister pack plastic.

 

[bradblack]

test the fuel pressure. that way you can rule out all the fuel supply system.

rotation sensors can do weird things. as has been said, check the gap and drop it a lot to see if it has an impact.

it happened right after you put fuel in it? get rid of the fuel and see if it has any pressure. i had a fuel filter blocked so solid it blew the hose off the inlet within 2km of filling up once. cut it open and laid the paper out - fuel wouldn't even seep through it.

 

[cornerhungry]

thanks all for the thoughts and ideas. Everyone that said it was fuel related , you were correct. After I metered out almost every sensor, relay, and fuse. I decided to revisit the fuel delivery. I pulled the injectors and cleaned them out. drained all the lines. Dreading that I would pinch the tank gasket i did it last. I guess I should have started there. Low and behold the fuel line had slipped off the top of the pump. The pump must have been creating enough pressure in the tank to allow it to idle and rev slightly. I refit the fuel line cleaned the crap out of the lower pump filter and carefully installed the base plate.

Fired right up ,

Thanks again all !!!!