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BF40D Bogging down to no-start condition

E

eastwardexpansion

New member
Hi All,

I have a BF40D that is having a peculiar problem that I cannot figure out. This is an intermittent issue that is becoming more prevalent. After running for a period of time (quite brief if at WOT) the engine will begin to bog down and bounce off of 4k RPMs. This is a rather long duration and quite aggressive die down and then surge up towards 4k before then repeating this process. Another condition is if the boat is idled for long enough it will die and refuse to restart. This results in a crank, no-start condition. The boat can be restarted (sometimes) by cycling the key and waiting multiple times to increase the fuel prime. This leads me to believe it is something on the high-pressure side of the fuel system.

Motor:
BF40D (BBDJ-110XXXX)
~2015 outboard
2600 hours
This boat is a Zodiac Pro 420 for a sailing organization. These boats accrue around 300 running hours a year. These are hard hours with lots of acceleration and the boats are really either in displacement mode or at WOT. Lubricants, plugs, and water separators are replaced at least twice a year (seasonal program); however, that is about it. Don't roast me, I have just become the one making the decisions about out maintenance.

Current diagnostics:
- Fuel water separator is new and not restrictive
- Internal fuel strainer is clean
- Primer bulb is hard and full of fuel
- No air seen in either filters (have not hooked up using clear tubing)
- Replaced VST filter which was absolutely disgusting (borderline black)
- Drained VST multiple times and it was clear and clean fuel
- Happens regardless of engine temp so does not seem to be thermostat/impeller related

Things I am wondering about...
- Is my next step to rebuild the VST?
- Are there any internal filters on the VST that could be clogged?
- Could this be injectors?
- Anything else I am missing?

Any help would be greatly appreciated.
 
Well, I've never worked on a 40 D. These are just some thoughts on what you are seeing.

Just guessing but your description of the fuel filter being black makes me think..... ....maybe not a VST rebuild.....but a very thorough scrubbing and inspection might be i⁷n order. With special attention given to the Inlet valve and float mechanism.

Even though you are seeing "clear, clean fuel" this does remind me of what happens with poor fuel quality and/or contamination. Have you taken a sample from the BOTTOM of the tank and let it settle for a few minutes?

This might also be symptoms of the HP pump failing. Running it with a fuel pressure gauge attached might yield useful information if you're in a position to do that.

Other things that come to mind are:
This also kinda/sorta sounds like a "power de-rate" scenario.

Is the green oil light on when the engine is running indicating adequate oil pressure?

I know you say it doesn't appear to be heat related but I see this engine has two temperature sensors. A bad sensor, sending false information to the control module, might cause a power de-rate condition.

And, there's the oxygen sensor. Those can cause problems too.

I don't know if unplugging sensors would be a reliable way to troubleshoot this but I think I might try, starting with the O2 sensor if you don't have access to a Dr.H diagnostic tool.

Unplugging sensors, one at a time, shouldn't cause any harm if disconnected and then reconnected with the ignition switch OFF.
This will, of course, log trouble codes.

If you decide to try that, it appears all the sensors are located on the port side of the engine. Hopefully they're not too hard to access. See the link below. Items 14, 15,16.

Honda Outboard 40HP OEM Parts Diagram for CYLINDER BLOCK | Boats.net

Buy OEM Parts for Honda Outboard 40HP CYLINDER BLOCK Diagram
www.boats.net www.boats.net

Less likely might be a problem with one of the two crankshaft position sensors. I always suspect connectors and wiring for things like that for being affected by vibration. If you want to have a look at those, you will need to remove the alternator cover. Items 5 times two in the link below

Honda Outboard 40HP OEM Parts Diagram for Alternator | Boats.net

Buy OEM Parts for Honda Outboard 40HP Alternator Diagram
www.boats.net www.boats.net

Same thing applies to the pulsar coil under the camshaft pulley. It's got a big, plastic plug connector and I've seen similar set-ups have connectivity issues. That area can collect water, dirt and oil in some engines. Item 10 in the link below

Honda Outboard 40HP OEM Parts Diagram for TIMING BELT | Boats.net

Buy OEM Parts for Honda Outboard 40HP TIMING BELT Diagram
www.boats.net www.boats.net

Wish I had a sure fire cure for ya but I don't even have the manual.

Good luck.
 
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