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BF50D "Rpm issue"

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SaltTime

Contributing Member
I'll try to keep this as short as I can. You guys helped me several months back with a new to me outboard and I was able to get it in running order. Here is the link to that thread.

2010 BF50D Fuel Pump issue

Ive recently purchased a bf50d outboard and have been troubleshooting and trying to get it to run correctly. From the beginning I was able to get it to run barely and stay at idle by first pouring fuel into the cylinders and it fired up and idled somewhat. I could rev it and it would hesitate a...
www.marineengine.com

I have an issue with the motor not wanting to go past about 4200rpms when I'm underway.

It starts every single time with no issue. The power from stop to getting on plane is perfect with no hesitation at all. As long as I keep the motor under 4200 rpm all seems normal. Its when it gets in that range that it just kinda "clips" if i had to use a word describe it. Almost like its hitting a rev limiter. It doesn't really bog or get jerky, it just simply stops accelerating and stays exactly at that 4200 rpm range, once i back off to about 4000 it runs perfectly again. The idle is not perfect, but its never wanted to die on me. It does kind of hunt up and down about 75rpm every 5-6 seconds at idle, but that maybe could be from someone messing with the idle screws before me....I'm unsure.

When i first started using the boat I thought it was just the prop cavitating or aerating because the boat has a tunnel, but once I was able to try a different prop "smaller one" it did the same thing at the same rpm just at a slower speed.

Ive checked fuel pressure while at idle and up to about 2500rpms with muffs on and it stayed rock solid at about 42psi. I didn't want to rev it up to the 4000rpm range to see what it did.

I had cleared the codes awhile back just to kind of start from fresh because people were trying to fix the motor before me so i figured id start fresh. I took it out a few times and it showed a single code of " long, long, long, long...etc" which i read could be an o2 sensor or a bad coil or misfiring spark plug. I cleaned the o2 sensor and cleared the codes again. Took it out once the other day and now its not showing any codes. The MIL light just stays on constant.

What I've replaced : All honda OEM parts from boats.net

high pressure fuel pump
all 3 injectors
high pressure fuel pump plastic filter housing
new spark plugs
new fuel line from tank to motor fuel connection
brand new non ethanol gas since ive been using it
also new o-rings for the vst tank "cleaned it and flushed all lines before hooking up injectors
also i trimmed the rubber piece that the high pressure fuel pump nozzle connects to as well.

I'm fairly sure I have my tachometer hooked up correctly as i have it set as "3 pulse" and its showing an idling rpm of about 850 or so depending if its in the water or on muffs. Hopefully I've explained this to make it understandable as to what its doing.

Thanks for the help everyone.

Also forgot to mention that Ive tried pumping the bulb while the problem is occurring and it doesn't change the condition.
 
My apologies if I over complicated the post….is it possible for the ecm to kick off the ignition or injectors when it gets to that rpm range you think? I wish there was a Honda service center close to me but there isn’t, that’s why I’m here. I just have run out of ideas of what to start chasing now.

I guess I’ll take it out a few more times and see if I can make it produce any codes.
 
SaltTime said:
My apologies if I over complicated the post….is it possible for the ecm to kick off the ignition or injectors when it gets to that rpm range you think? I wish there was a Honda service center close to me but there isn’t, that’s why I’m here. I just have run out of ideas of what to start chasing now.

I guess I’ll take it out a few more times and see if I can make it produce any codes.
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Had a similar issue with BF50D & turned out to be 02 sensor. Runs sweet as now.
Good luck .
 
Check to make sure tachometer is set correctly.----And if you are hitting the rev limiter you may need to go to a BIGGER prop ( more pitch ) I think.-----Why is the tachometer on " 3 pulses " on this motor?
 
racerone said:
Check to make sure tachometer is set correctly.----And if you are hitting the rev limiter you may need to go to a BIGGER prop ( more pitch ) I think.-----Why is the tachometer on " 3 pulses " on this motor?
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I believe it’s a 6 pole motor, and I read that you half that number to convert to pulses on a tachometer. I tried the other settings and it was the closest one to stock idle rpm as well. If I’m wrong please let me know.

I have the OEM shop manual now so I’m trying to decipher it and hopefully find something without just blindly throwing parts at it.
 
SaltTime said:
Thank you for the suggestion. Did you have any alarm or codes being produced when the issue would occur?
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No alarm ,but o2 code was there. The motor was using excess fuel as well & surging at idle.
Its a completely different motor with the new sensor.
 
I have been diagnosing quite a bit as I’ve got the shop manual and have been resetting the ecm as of recently so I’ll have to run it on the water to get a true feeling as if I have any real codes. I was under the impression that an o2 sensor would make an audible alarm, but since in your case it didn’t Denis I will keep a sharp eye out for that particular code.

From my troubleshooting since getting the shop manual I’ve checked the coils and the primary resistance is about 2.2ohms, right within spec. As I moved onto the secondary resistance as the book shows…I am getting 20-21k on all three coils with only a slight variance between them. The book says they should be within 9-11k.

Does it sound possible that all the coils have some sort of resistance in the main spark plug wire but the coils themselves are good? I don’t know how many hours this motor has, but I do know it was on a work barge before I got it. So it could possibly have a lot of time on it idk. It’s hard for me to believe all the coils would be out of range by that amount. But the book wouldn’t lie on its values.

I posted the page so maybe you guys could have an opinion on it.

:

On the tach question, after researching I found a couple places where they said to divide the poles by half and that would be your pulse amount. I’m learning as I go tbh..thanks for any help.
 

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racerone said:
" It was on a work barge "-----Did you do your first trip with the same prop that was on the barge ?
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Yes, it has the original aluminum Honda prop whicg had slight wear but nothing bad. I’ve also tried a smaller diameter prop and at the exact rpm it starts to clip out. I would think the problem rpm range would change but it doesn’t, just gets to the problem area faster with less throttle at a lower speed.
 
You are likely hitting a rev limiter.----When installing a motor that came off a barge you need to consult a shop to determine the correct prop for your boat.----Going to a smaller prop to get the revs up may have been futile.---Sorry if that is blunt.
 
racerone has a good point , my motor came off a houseboat & had 11 1/8 x10 pitch prop & it hit the rev limiter on my
4,7m tinnie , so I went to a 11 1/8 x13 pitch & it worked fine.
 
If your motor is hitting the rev limiter the tacho must be wrong, my rev limiter would start at 6200
rpm. The motor would start missing at those revs, I first thought I had a motor issue until I changed props.
 
pretty sure I have my tach set correctly as the idle speed is about 900, I suspect there’s another issue because the motor just doesn’t get to that “scream” sound and feel. Thanks for the suggestions though, I will update if I find a fix.

If anyone has any experience checking coils and reads what I have posted above and has an opinion on how those coils ohm’d lemme know thanks.
 
SaltTime said:
pretty sure I have my tach set correctly as the idle speed is about 900, I suspect there’s another issue because the motor just doesn’t get to that “scream” sound and feel. Thanks for the suggestions though, I will update if I find a fix.

If anyone has any experience checking coils and reads what I have posted above and has an opinion on how those coils ohm’d lemme know thanks.
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Just curious as to the size & pitch of your prop & size & type of boat . I bought 2 of these motors off the same houseboat
I fitted one with tiller steer & tried on my sons tinnie & it would start missing at 30kph. The motor certainly didn't sound
to be over revving so I tried swapping electrical parts from the other motor , all to no avail. It wasn't till I fitted the other motor to a 15 ft
boat with forward controls & a tacho that I found they were reaching the rev limiter. As they came off a houseboat they both had
10" pitch props. After fitting them with 13" props both boats went to about 50kph & no rev limiter.
I'm still of the opinion your tacho could be wrong, as believe me these motors don't sound to be screaming like2 strokes do,
 
A word on tachometer setting. The EFI get tacho signal from the ecm, not the alternator. The usual setting with a Honda tacho is 1. It sounds very much like it is over revving and you're chasing a problem that doesn't exist
 
iang6766 said:
A word on tachometer setting. The EFI get tacho signal from the ecm, not the alternator. The usual setting with a Honda tacho is 1. It sounds very much like it is over revving and you're chasing a problem that doesn't exist
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hmmm interesting, I installed this tachometer

Sierra International 58255P Tach 7K​

I have it set to the 3p/6c as it seemed to have the closest normal idle speed. Is it possible this tachometer is not compatible with my engine? Have you ever heard of that happening? Here’s a pic of the back, there is no option for a 3cylinder engine so I just went with the pulse setting that I found online and like I said before I kind of went with the idle speed.
 

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That will work but not accurate. The important rev range is wide open throttle so you can prop the boat correctly. To see if it is accurate at the top of the rev range, just trim out until it hits rev limit which should be around 6400rpm
 
iang6766 said:
That will work but not accurate. The important rev range is wide open throttle so you can prop the boat correctly. To see if it is accurate at the top of the rev range, just trim out until it hits rev limit which should be around 6400rpm
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I can get the boat cruising on top and, like you say I start to trim the motor out and at about 4200-4300 according to the current tachometer it starts clipping out and won’t accelerate anymore. I can reduce throttle and it will be fine until I increase trim or throttle, then it starts to do it again.

I know my fuel situation is good. I recently bought the OEM shop manual and performed all the volume and pressure tests that were in the book and there’s definitely no problems there which i can find.

My trim angle sensor is broken completely out, but there was no mention in the shop manual that the angle sensor would effect the motors rpm’s….i need to email Honda with that question as I don’t want to spend the money on that because I really don’t need it and it would be money wasted.

I’m willing to spend some more money, but I just hate throwing parts without knowing fully well its actually the issue.

The coils were out of range on the secondary resistance test a significant amount, the book says 9-11k I believe and they were around 20-21k. I just have a hard time believing all 3 coils are bad and all the exact same resistance, as I can pull each plug boot while running and can probably jump a 1/2” spark no problem. Not a scientific test though.

Also , the o2 sensor seems really lazy when I bench tested it, very slow to respond up or down. But I’m not getting any alarms or o2 codes.

Sry for rambling, but this is my only therapy between work and trying to fix it lol. I’m not gonna give up.
 
Sounds like you're chasing a fault that isn't there. You're tacho is way out and the wrong one. Best tacho is through your NMEA 2000, straight out of the ecm. I never resistance check coils, I only check output using a DVA meter. They should push out about 5v at cranking speed. Stator is for charging only, ecm runs off battery voltage. Hope this helps
 
iang6766 said:
Sounds like you're chasing a fault that isn't there. You're tacho is way out and the wrong one. Best tacho is through your NMEA 2000, straight out of the ecm. I never resistance check coils, I only check output using a DVA meter. They should push out about 5v at cranking speed. Stator is for charging only, ecm runs off battery voltage. Hope this helps
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thank you iang, I googled that type of tach and it’s it looks like that is a bit out of my price range, and I don’t have that dva meter adapter thing. If I’m able to find something tomorrow I will update. Thanks again fellas
 
Got some time today and resistance checked the throttle body and had a smooth sweep from zero to wide open throttle and back again…also voltage tested it with key on and with the throttle linkage still attached using binnacle I got .60v at zero and rode the voltage up slowly to 4.54 and back a few times with no deviation. Not sure exactly what the best numbers would be but I’m pretty sure those are close.

Bench tested the o2 sensor as well and the heater had 7k resistance I believe and when I used signal and ground the voltage climbed up to about .9v with slow heat from a torch and when I’d take it off it would drop fairly quickly to about .3v and was a little slower from .3v to .1v, but not nearly as fast as ones I saw on YouTube being tested….maybe it’s a little lazy?

The idle is still choppy and it hunts from about 800 to 900rpm and back about every 3-4 seconds. Guess I’ll just have to enjoy going a little slower on the water for now until I find what’s wrong or find something else to put on the boat.

Also was excited for a bit because when I resistance tested the TPS my meter was going to O.L at half sweep, until I noticed it was set to the wrong value of 2k instead of 20k. lol

Anywho, maybe it is the ecm and I’m just chasing my tail. NSDON, I will try to get my hands on a secondary tach and compare like you said as well….but I tried the 2pulse as well as 4 pulse and they were both obviously reading incorrectly at idle. Thanks everyone
 
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