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2002 BF225A chokes over 4000 rpm after several hrs of running

OK I talked to the boat grotto in SD this morning, just fact finding. So here is what he told me. 2001-2009 honda outboards 200 and up all have ECMs that fail. It was a known issue and the ECM is non-repairable and they all fail. He said he has worked on countless of these motors with all the same issue. When I described this it was his instant response and a repower was the only real solution as even another sourced ECM would potentially have the same problem. I of course thanked him for the information and then spooled up AI to look for anything out there that supported this theory. AI had the opposite statement saying they are actually very robust.. thoughts?

In the AI session another possibility was identified. I replaced the failing oem O2 sensor with a cheap amazon sensor with 5 star rating.. AI flagged this as the potential root cause of all my problems stating that Honda ECMs are very sensitive to sensors reporting exact readings... so thinking I have to spring for a 300.00 O2 sensor...

Thoughts?
 
I have bought a used O2 sensor from ebay to check this out... Theory is worst case I get an O2 alarm and I can get past the 4K limit... Worst case its something else and nothing changes... Pretty solid AI response from both chatgpt and gemini that the aftermarket sensors are a big no no
 
I have an 04' 225 for 22 years, no ecm issues. The only regular issues with that generation of V6 are 02 sensor, vertical shaft bushing, crankshaft thrust bearings and corrosion issues. An o2 sensor issue will trigger an intermittent alarm after idling for a few minutes. o2 sensor only affects a/f mixture from idle up to 2500rpm, all map after that.

Easy test for o2 sensor, launch the boat and get to open water. turn off the engine for a few minutes then restart and immediately accelerate to over 3000 rpm and keep it there. If intermittent alarm comes back its either water in fuel, charging or battery issues.

A steady alarm is serious, either overheat or low oil pressure, stop engine immediately. Find another mechanic, running DR H diagnostics will tell you exactly what's alarming. The first thing I would do is check the fuel pressure at idle and under full power. If you do need an ECM they sell them all the time used on ebay.
 
I'm definitly not the guy to ask or believe about this but it is entirely possible you're on the right track. I have seen a few cases here where the O2 sensor "made the diffeeence".

I'm confident Honda had plenty of O2 problems with the early V6 outboards and, I don't know for sure, but I think they moved away from using O2 sensors for fuel control a few years ago because of those issues.

Additionally, there are guys on this site...chawk_man for instance...that are still running their well cared for, pre 2007, big Honda outboards. And though I'm not positive, they may still be on the original ECU

Hopefully they'll speak up about what they've seen.
 
123jayyyy said:
I have an 04' 225 for 22 years, no ecm issues. The only regular issues with that generation of V6 are 02 sensor, vertical shaft bushing, crankshaft thrust bearings and corrosion issues. An o2 sensor issue will trigger an intermittent alarm after idling for a few minutes. o2 sensor only affects a/f mixture from idle up to 2500rpm, all map after that.

Easy test for o2 sensor, launch the boat and get to open water. turn off the engine for a few minutes then restart and immediately accelerate to over 3000 rpm and keep it there. If intermittent alarm comes back its either water in fuel, charging or battery issues.

A steady alarm is serious, either overheat or low oil pressure, stop engine immediately. Find another mechanic, running DR H diagnostics will tell you exactly what's alarming. The first thing I would do is check the fuel pressure at idle and under full power. If you do need an ECM they sell them all the time used on ebay.
Click to expand...
ok good info and this aligns with what happened initially. The boat would idle for about 2-3 min and then alarm. turn it off and turn it on and alarm would go away for about the same time idling. Anything over idle did not trip an alarm.

I replace the O2 sensor and the alarms all went away. but now I have this choking or surging or searching over 4K rpms. I assumed it was filters as it will run for 3-4 hrs normally running from spot to spot or trolling and then this happens last 3 trips out. Which leads me to think its a heat soak thing or caused by trolling at 7-10 knots for an hr or so.. I currently have no alarms or codes being thrown

I have two water fuel separators and both have no moisture in them

If I understand what your saying the O2 sensor isnt part of the computer map over 2500 so shouldnt be affecting how the motor runs at higher rpm.

my next steps:

1. O2 sensor replace the Chinese one with the honda one
2. low pressure fuel pump
3. Pull and clean the VST
4. get a fuel pressure rail gauge
 
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That system isnā€™t currently functioning it is stuck in the wide open position. Itā€™s on the todo list. Iā€™m led to believe that the wide open position is where the butterflies would be in running the motor over 4000 RPM.
 
While you have the Vst out pull the high pressure pump and check the screen in the insulator, they clog easily. Unless it's brand new you'll break the plastic insulator when you remove it so have a new one ready.
 
So a bit of an update: I was able to disassemble the air bypass flapper things inside the intake manifold and get them functioning with the vacumm actuator. I installed the new to me used 02 sensor and so fare on the muffs it doesn't seem to be alarming. Also installed a new to me used low pressure fuel pump. again every thing seems to be working.. We just had a storm hit so cal so maybe next weekend I will get a test run in...

Also I pulled all the plugs and checked them. I did notice some engine oil in the hole of the bottom 2 plugs on each side. I assume this is just a leaky valve cover gasket. I cleaned it all out, and reinstalled the plugs... Plugs have about 20 or so hrs on them and they looked clean.

I ordered all the seal and so forth for the vst swap..

I was looking to install an engine water temp guage and interesting there isn't a port available on the honda motors for an aftermarket water temp guage. Has anyone done the direct surface mount ones?

Also I read that I can get a nmea 2000 cable and all my diagnostics will read into the nmea system and can be displayed on on my chartplotter. Has anyone installed one of these cables? Seems plug and play.
 
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