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BF 50D Runs poorly @ high rpm

BF50D

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I bought a used 2011 pontoon boat with a same year Honda BF50D from a boat dealer this summer. I had it for a month during which it ran well, then suddenly started running poorly at full throttle. The dealer has been real good at working on it, no charge, but not getting any results on a solution. They feel that the rev limiter is shutting the engine down. It was sent to an authorized Honda service dealer, where they dropped the engine an inch and changed the propeller with no change in performance.
I'm wondering if there isn't another problem that's being overlooked? I read about a fuel pump, or pump diaphragm possibly being an issue?
Any suggestions for possible alternative causes would be appreciated.
 
If a Honda dealer is looking at it, a good start is to run it with a fuel pressure gauge and see what's happening. Not sure why they would mess around with eng height etc if it used to run well. The grommet on the pressure side of the high pressure fuel pump is a common culprit for cause reduced fuel flow, but your dealer should know about this
 
hmmm.
If they thought the engine protection system is shutting the engine down then they should have been thinking about an over overheat scenario. Did they mention that to you? Even if the engine is cooling properly a bad temperature sensor could cause this sort of issue.

If the engine is being "de-rated" but not shutting off there may be an engine oil pressure connection. Again, pressure could be fine but a faulty sensor could cause the engine to power down. When an engine goes into de-power due to overheat or low oil pressure it will usually return to normal, for a short time at least, when the ignition is turned off and it is restarted. Is yours behaving that way?

As Ian pointed out, if it ran well before, what was their justification for altering outboard height?

Completely agree that checking fuel pressure while the fault is occurring is indicated here. Did either shop do that?

Other things that come to mind might be a faulty crankshaft position sensor, faulty load sensor (MAP), valve train issue or even a loose connection in the ignition wiring. Even a bad alternator will occasionally affect how an engine runs.

Good luck.
 
2 things- I have just about zero confidence in dealers to start with, so when I hear of one lowering the engine to repair an engine having trouble making power at high rpm, I'm thinking I would be speaking with a different dealer - if not Honda directly. I'd also be asking to have the engine put back where it was originally - at their expense. Regarding that grommet on the high pressure side of the pump, my somewhat limited experience (as compared to others here) would tell me this is generally an issue only if the vapor separator has been apart and the fuel pump removed. That being the case, it's extremely likely to be an issue. Further, a pressure test would reveal that issue pretty much immediately. Beyond that, I'm assuming that there are no trouble codes being thrown? Wouldn't temp and oil pressure issues record an error? Either way, if there were an issue with a sensor or an actual issue with the motor. If there is a heat issue, has a t-stat been changed? Is there a chance that the replacement is the 180 degree unit used on the older 50's rather than the 160 (I think?) used in the fuelies? Best of luck. These fuelies are great - until they aren't. MUCH more difficult to troubleshoot/diagnose than the carbed engines.
 
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Thank You all for the replies.
I've gotten all limited information second hand from the selling dealer. He was upset with the Honda dealer having had the boat for 3 weeks and no solution. Supposedly the engine was lowered to address a cavitation issue thought to be triggering the rev limiter. I was told the Honda dealer replaced a high pressure fuel filter & installed a thermostat which had been missing. In reference to the comment about a possible bad temperature sensor, maybe sometime in the engines history someone removed the stat to address a heat issue? The engine never returns to normal performance regardless of time interval between operation.
If there were a valve train issue, would engine performance be affected at low rpm? The engine starts right up and performs well up to approximately 4k rpms. Beyond that rev point the engine sputters and stumbles.
Thanks for the help.
 
Though I believe it's pretty unlikely, if it were a valve train issue it could be EASILY identified by a compression test that shouldn't take more than half an hour tops. USUALLY valve train issues make themselves known at all rpm.
 
Well...
Yes, a valve train problem COULD manifest itself at higher rpm. Consider a weak or broken valve return spring. At low rpm a weak spring can "keep up" with doing it's one and only job....closing the valve on time. At higher rpm it might not.
BUT....please don't get hung up on that. It's just an idea that, at some point, when all else doesn't pan out, could be an avenue of investigation.
AND...while a "static" compression test will NOT always reveal a fault like that, it is still a valid test to perform to gain some possible insight into the health of an engine. A "running" compression test could also be indicated here to identify cylinder sealing during off idle operation.

Again though, since you're not the mechanic, you are in a position where you need to gather what information you can and ask lots of questions.

The info you gave us initially was incomplete. You updated with the fact that the high pressure fuel filter had been replaced. Was that before the problem started or after? If before then the problem may have been introduced during that service.

Yes, people do typically remove the thermostat in a misguided attempt to solve an overheat condition. I mean....why else would someone do that?
While it might not be related to what's happening now I can't say that I would look at it as a "good sign". But since you said it ran ok before it would seem that the engine didn't suffer any major damage.

If you're paying for the time, you're entitled to ask questions. Did they hook up Dr.H at the dealer to check for codes? If so, they have the ability to print out the operating parameters during the test. There might be some useful info there and you should ask for a copy. Especially if you end up needing to take it somewhere else for further diagnosis.

Good luck.
 
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