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2016 BF250 stalls at idle at drops Rpms while cruising

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Lmoore87

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I have a 2016 Honda BF250 that starting surging at idle and now the surging is gone but it will stall while idling. Doesn’t matter if it’s on the hose or in the water it will idle smooth for 5-10 secs and stall. Always starts right back up. If you bump the throttle up a little bit it will idle without stalling. Also after getting on plane it will drop 4 or 500 rpms from whatever rpm you are cruising at. Go back to idle plane off again and it will do the same thing. Doesn’t matter if you run 4500 or 3000 rpms it will drop 4 or 500 rpms after holding for 5 secs or so. It also feels like it has lost a few hundred rpms on top end. I ran it for about 2 hours this past weekend and ran fine the whole time besides what’s mentioned above. I put a new set of spark plugs in it, drained all of the engine separators and vst tank, changed the HP filter changed the separator/filter on the boat, cleaned the iac screen, cleaned the screen behind the regulator on the fuel rail, freed up the stuck IAB flaps in the manifold, checked valve clearances and used suggested clearances from another thread I read through, removed the low pressure pump and hand operated it to make sure it was pumping good, looked over all the vacuum lines while the manifold was removed cleaned the throttle body and ran it on an external 6 gallon tank. It doesn’t have any warnings or check engine light. Any ideas on what I should try. Forgot to mention I also pulled the thermostats to verify they were opening and closing properly
 
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Hi Lmoore,

Welcome to the forum. Hopefully you've already found a solution.

I've been waiting for the smart kids to answer you because I have only just seen a 250 live and in person. Never touched one though.

But, you're looking for ideas so I'll give it a shot.

This sounds to me like there could be something going on inside the VST like maybe some "trash" or a sticky float or needle valve.

Like I said, never worked on one so I've no idea how much trouble it would be0 to open it up for cleaning/inspection.

Something else that might effect the way the fuel float and inlet valve is working is the vent system for the VST tank. If the filter (item 8 in link below) is dirty or the check valve (item 18) is stuck and blocking air flow, then it might interfere with the fuel level in the tank being properly maintained.


Did you see dirt build up on the IAC screen when you cleaned it? If so, that would prompt me to want to clean the throttle body. Actually, I would clean it anyway to see if it might change the symptoms.
You said that you checked vacuum hoses but double check the MAP hose where it slides on the nipple. They crack and leak there on most engines. You might also check the MAP oring condition.

The VTEC solenoid (spool valve) has a filter screen (item.19 in link below) that could affect control oil pressure if it gets dirty/plugged. Not sure it would cause your symptoms but thought I'd mention it. I wouldn't try to reuse the seal/filter so you should probably have a replacement on hand if you decide to take a look. Your choice though.



The fact that you had to un-stick the IAB could indicate there's more to do in there so, hopefully, chawk_man, Ian or others will comment soon.

Just some guesses.

Good luck.
 
Thank you for the suggestions. I haven’t checked anything inside the VST or checked the filter and check valve. Should have done all of those things while I had the manifold off but it’s not really a big deal to remove it. I did drain the VST but I guess there’s more going on in there than I realized. I thought it was just a tank with a pump inside of it so that will be my next task. I also have a 2007 200 that was given to me but isn’t much good for anything since it went for a dive in saltwater but a lot of the parts look interchangeable. Heads, intake manifolds, exhaust manifolds and the VST looks to be the same just has a little bit different filter setup on the back lower left side. Low pressure pump also looks the same. I’ll pull the VST and make sure to report back. I hate reading through threads and not seeing the solution to a problem. Thanks again.
 
Yes, I see plenty of write-ups here and on other sites I use that either go unsolved or, the guy is so eager to get back out there, he never updates.

I wanted to point out to you that, on some V-6 Honda engines, there have been posts about the water hoses with 90 degree bends at the exhaust manifold get partially plugged. See items 6, 7, 8, 9 in the link below.


Not likely causing your complaint but just something to check to prevent overheating.

When you cleaned the throttle body, did you remove it and clean both sides of the plate?

You are probably near entering a phase of diagnosis that will require checking fuel pressure and connecting the Dr.H software to get better information for solving this. Looking forward to seeing you report back some success.

Good luck.
 
Had sometime this evening and pulled the manifold and vst off. VST was super clean and the float seemed to be working properly. I was able to blow through the line when the float was in the down position and not able to when it was in the up position. Checked all of the filters again and they were all clean. Checked the two check valves. One up top and one on the bottom and they both worked correctly. Checked my vacuum lines for cracks and leaks and they all looked good. The vacuum canister still had vacuum on it when I unhooked the lower gray line with the check valve in it. I ran the motor before this hoping it would idle correctly lol. But of course it didn’t. Tried to see if it had any codes but still didn’t. I idled it up with the binnacle and lost a few hundred rpms after 5 or 19 secs so it’s doing the same thing. I haven’t got my o2 sensor yet to try that but the one on the parts motor I have has a bigger threaded portion where it goes in the bung so those parts are not interchangeable. I also opened the IAB flaps and put my finger over the vacuum diaphragm port and they only closed a little and the diaphragm held them open until I pulled my finger off. Any more suggestions before I put all of this stuff back together? I guess once this is back together I’ll figure out how to check fuel pressure and try a new o2 sensor. Motor has 572 hrs. Thanks for the suggestions
IMG_9801.jpeg
 
Lmoore87 said:
I have a 2016 Honda BF250 that starting surging at idle and now the surging is gone but it will stall while idling. Doesn’t matter if it’s on the hose or in the water it will idle smooth for 5-10 secs and stall. Always starts right back up. If you bump the throttle up a little bit it will idle without stalling. Also after getting on plane it will drop 4 or 500 rpms from whatever rpm you are cruising at. Go back to idle plane off again and it will do the same thing. Doesn’t matter if you run 4500 or 3000 rpms it will drop 4 or 500 rpms after holding for 5 secs or so. It also feels like it has lost a few hundred rpms on top end. I ran it for about 2 hours this past weekend and ran fine the whole time besides what’s mentioned above. I put a new set of spark plugs in it, drained all of the engine separators and vst tank, changed the HP filter changed the separator/filter on the boat, cleaned the iac screen, cleaned the screen behind the regulator on the fuel rail, freed up the stuck IAB flaps in the manifold, checked valve clearances and used suggested clearances from another thread I read through, removed the low pressure pump and hand operated it to make sure it was pumping good, looked over all the vacuum lines while the manifold was removed cleaned the throttle body and ran it on an external 6 gallon tank. It doesn’t have any warnings or check engine light. Any ideas on what I should try. Forgot to mention I also pulled the thermostats to verify they were opening and closing properly
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I have exactly the same problem with my four year old BF250 for almost one month. The Honda service agent has also replaced the O2 sensor some weeks ago. Last week he removed and cleaned all the injectors. We have also swapped out the ECU. I still have exactly the same problem you have with declining rpm over a short time period. This happens regardless of the sped and rpm you select, at six knots or 25 knots. The boat speed and rpm gradually decrease and then suddenly jump back up to the initial setting and then it repeats the process again.
Honda New Zealand have nothing to offer as to what the problem may be.
 
Hard to help without a full description of what the dealer has done.There is a fine screen under the high pressure fuel pump insude the vapour separator, has tis been checked/ cleaned? Has fuel pressure been checked whilst the motor is running under load? This definitely sounds like a fuel supply issue. A data recording when problem is present would also be useful to help solve the issue. I'm surprised NZ Honda can't fux this issue, is it still under warranty?
 
Just had another thought, I once had one with these symptoms and it turned out to be a leaking lower seal where the manifold goes into the lower mountcase exhaust, a fine mist of water was spraying up onto the O2 sensor. Something to check if your manifolds have been off for anode replacement.
 
iang6766 said:
Hard to help without a full description of what the dealer has done.There is a fine screen under the high pressure fuel pump insude the vapour separator, has tis been checked/ cleaned? Has fuel pressure been checked whilst the motor is running under load? This definitely sounds like a fuel supply issue. A data recording when problem is present would also be useful to help solve the issue. I'm surprised NZ Honda can't fux this issue, is it still under warranty?
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I’ve been with the mechanic when we’ve had lap top connected and on a call to Honda more than once. No issues with fuel supply pressure, that was the logical first port of call. Had previously had issues with the O2 sensor and replaced it. Next step is to replace the VST and IAC valve.
It’s not under warranty but you would have to say support is questionable. Will report back tomorrow after I give it another in water test.
One thing I do find a little alarming for a motor of this age is the level of corrosion caused by the use of unsuitable metals in some parts. Great for fresh water, not so great for salt. I’ll report back tomorrow after I’ve water tested.
 
I don't believe it's IAC related. It would not cause a surge in the midrange. I've worked on these motors for a long time and I'm still think it's O2 sensor related, it would be good to see a recording of the values and see how quickly it's reacting to changing conditions in the exhaust.
 
Yesterday we replaced the VST and IAC valve. In water tested an d the problem remains the same. We also swapped out the ECU just because we had one. Also checked the spark plugs for any sign of wetness. The plugs and O2 sensor is only six months old. The mechanic saved two segments of testing at different speed settings to send to Honda mechanic. They couldn’t see anything before and it appears nothing has changed but let’s wait and see.
 
Try another O2 sensor, they were extremely troublesome, don't assume it's fine because it's only 6mnths old. I've had them fail that early, biggest issue with the V6 Honda's the reason they deleted them from the D series engines, because they couldn't get it right. Result is a motor that uses 10% more fuel than the O2 sensor equipped models.
 
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