BF40D limp mode

What are the reasons for a Honda BF40D to go into limp mode after about 10-12 minutes of running?

By limp mode I mean, the rpm's that started at 2-3000 are now maxed out at 1800 and then cycled down to 1400 for a second or two then back to 1800 for about 30 seconds then down again to ~`1400, then back again with no response to increasing the throttle. The time at 1800 is shorter and shorter, until the engine stops and will not restart. There is also good stream out the pee hole. The water out the pee hole is not hot but just a very little bit warmer than the lake water.

The oil lamp is green and stays green. No MIL flashes or any other lamps come on.

Thanks for your responses.

My bet is it's hot. When was the last time anyone had a good look at the impeller?

I recently replaced the impeller in the lower unit and housing seal as well. this is a 2012 btw. I also replaced the thermostat. I have not opened up the water jacket yet. I was thinking about checking it out.

A few ideas. Random order....

Are you running this motor on land (muffs or bucket?)?

Does the motor SEEM hot to touch? Maybe steam from the exhaust port?

Is this motor being run in salt water?

Was the inside of the thermostat housing all crudded up?

Have you checked your fuel filters? Do any of the gas line fittings appear to be wet, like they may be leaking?

What does the primer bulb look/feel like when the motor drops rpm? Is it still firm, collapsed, or soft? Have you tried using it to see if your rpms pick back up?

Has the VST been apart recently?

Hi, I really appreciate everyone taking the time to respond.

Are you running this motor on land (muffs or bucket?)?I am running this from the boat ramp while still on the trailer. I understand there are some intakes that require taping if using muffs. I don't trust tape, so I'm running the motor with it submerged in the lake.

Does the motor SEEM hot to touch? I had the cover off while I test ran the motor. While I did not touch the motor, I did not feel any excess heat. I did feel the pee stream when I first started the motor and it was strong flow and cold at both idle and 2,000 rpm. When the motor started the limp mode I felt the pee stream and it was not cold but not hot either, say luke warm.

Maybe steam from the exhaust port? I did not see any steam from the motor anywhere.

Is this motor being run in salt water?No. I bought this boat from a gentleman who said it was only run in fresh water and did not have many hours on the boat/motor. When inspecting the motor it looks almost brand new. I have not found any signs of salt water usage or salt residue. It was in a storage unit when I purchased. I suspect it may have sat for a while. We took it to the lake, launched the boat, it ran fine for 15 minutes up to 30mph and loaded it back on the trailer. no problems. I brought the boat home by highway about 2.5 hours. Then this issue started.

Was the inside of the thermostat housing all crudded up? No. I suspected the thermostat was sticking when the limp mode first started, so I purchased a Honda thermostat for this motor S/N and gasket and replaced. The housing was really clean.

Have you checked your fuel filters?I have checked both filters. Cleaned out the low pressure filter and replaced the high pressure filter. The high pressure filter was a light to medium brown and I found no debris in the filter.

Do any of the gas line fittings appear to be wet, like they may be leaking?I found a small wet/leaking fuel line, fuel tube B that connects between the low pressure filter and the low pressure fuel pump. I replaced this fuel line with a new one and new clips. I watched this fuel tube on the last test run. No leakage. I observed no leakage at the low pressure fuel pump connections either.

What does the primer bulb look/feel like when the motor drops rpm? Soft, like half full. Not hard/firm. I suspected this might be a problem with air leakage, so I replaced the fuel tube and bulb between the fuel tank and motor.

Is it still firm, collapsed, or soft? Have you tried using it to see if your rpms pick back up? No. I only checked the bulb midway during the test run and after the engine died and would not restart. The bulb was not ever firm, but soft and it felt like some fuel in the bulb.

Has the VST been apart recently? No. I'm trying to determine next steps and taking the VST apart for inspection is one item on the list.

Consider that there is a potential for leaks (sucking air) from the primer bulb to the actual pool of fuel in the tank as well.

"What does the primer bulb look/feel like when the motor drops rpm? Soft, like half full. Not hard/firm. I suspected this might be a problem with air leakage, so I replaced the fuel tube and bulb between the fuel tank and motor."


From your description of the pee stream, It sounds like you cooling is probably not the issue.

So one last idea - do you have another fuel line and fuel tank available to you? There's also the potential for the fuel hose to break down and collapse internally.

Ok, I'll look at cleaning the fuel tank. I already replaced the fuel line from the bulb to the fuel tank.

1) good idea? To help rule out the thermostat, I was thinking of pulling the thermostat, reseal the cover and run the engine without a thermostat. This would allow water to pass the thermostat and answer if the thermostat is the problem.

2) I assume if water is coming out of the pee tube that the water has traveled from the water pump impeller up into the water jacket, up to the thermostat and either a) back down and out the pee tube when thermostat is closed or b) up into the engine heads and then out the pee tube when the thermostat is open?

Thanks.

zsam1 said:

Ok, I'll look at cleaning the fuel tank. I already replaced the fuel line from the bulb to the fuel tank.

1) good idea? To help rule out the thermostat, I was thinking of pulling the thermostat, reseal the cover and run the engine without a thermostat. This would allow water to pass the thermostat and answer if the thermostat is the problem.

2) I assume if water is coming out of the pee tube that the water has traveled from the water pump impeller up into the water jacket, up to the thermostat and either a) back down and out the pee tube when thermostat is closed or b) up into the engine heads and then out the pee tube when the thermostat is open?

Thanks.

Click to expand...

You know what they say about assumptions...

Just FYI (not really important) Pee water supply sort of "tee's" off the passage leading up to the thermostat (t-stat) area. It does NOT flow through the block. This passage (from the t-stat side of the block to the side with the pisser) is located in a passage that runs between the block and the middle section (under the block).

You won't hurt anything running it without a t-stat, just don't forget to put it back in or try to leave it out. Without it, (and I've seen a LOT of these) the motor will gum up the rings, eventually dropping the compression down into the 80's where they become difficult to start.... Many times this will lead and inexperienced dealer telling you that you need to rebuild the motor, or get a new one. I love buying these, because they can be fixed with just a little time and a few gaskets. They just need to have the rings "unstuck" and ring lands cleaned. Reassembled afterward, compression will be restored to acceptable limits. Point being, go ahead and remove it for trouble shooting, but don't let anyone tell you they can be left out permanently.......

If the motor were getting hot, that pisser get's pretty darn warm, even though it doesn't actually go through the block.

Do you have access to an infra red thermometer? They're not expensive if not (<25 bucks), and will tell you in very short order whether or not the motor is overheating. -Al

Hi,
I obtained an infrared thermometer. Here are the results:

Tested on the ramp, sitting on the trailer at the lake.
Time -------------------Temperature (F)------------------------------------------------------
Front of motor Water jacket Between top and middle cylinders at spark plugs RPMs
0 62-66
1 116 800
2 136 2000
3 156 2000
4 101 152 2000
5 2000
6 92 101 157 3000 immediately started cutting out, running rough,
pee water barely warm


6:30 101 137 800 backed off the throttle in gear to idle,
pumped bulb became hard was mostly full,




7 79 101 146 800 oil lamp green, no temp lamp




8 tried to put in gear and accelerate and
response was choppy then died


xxx Tried to restart and would not start - primer bulb hard
switch off - then back on - green oil lamp and temp lamp come on for a second,
then 2 beeps and both go off
92 127 132 not running Fuel present in low pressure fuel filter

here this might show better

As I thought/mentioned, there is no temp. issue here....

More likely is a fuel delivery issue - somewhere.....

Guess I'll get a fuel pressure gauge and test:
1) fuel pressure measurement
2) pressure regulator
3) high pressure fuel pump output

Regarding the VST. If you take it apart and remove the high pressure fuel pump, you'll find the pump inserts into a hat shaped rubber grommet. That grommet has caused more headaches/heartaches than you can believe. Troubleshooting the problems with it VERY difficult!

Most guys will reassemble the pump into that grommet by placing the grommet into the housing, then pushing the pump into it and fastening the screws that secure it. Using that process, there is almost a 100% chance that grommet is going to bunch up on top of the pump and restrict the fuel flow. If not completely restricting it, it will not flow as designed for sure.

The fix to avoid that is simple. You slide the grommet onto the output side of the pump, then insert it into the housing and secure with the mounting screws.

That's why I asked if the VST has been apart......

After reading another thread you participated in for JUne/July 2020.. it seems my engine is having exactly the same problem - THE VST grommet.

I need to figure out all the o-rings, seals and gaskets to order to work on my vst.

also, which end and how much to cut off the grommet. I'm not clear on this.

Working carefully, you shouldn't need any parts (I don't use any).

As far as cutting the grommet, that's no longer necessary, as long as you slide it on to the outlet side of the pump, THEN reinstall.

When you have the grommet in your hand, you'll see that for some mysterious reason, that grommet only has a small hole in the top of it for the fuel to pass through. Early on, I was making that hole as large as possible. Now, with the new install method, cutting no longer necessary. Still wouldn't hurt anything to make it a little bit bigger.....

Hi,
the VST rebuild parts finally arrived. I have removed the VST. While removing a few observations:
1) when relieving high pressure fuel by loosening the relief bolt, hardly any fuel exited.
2) Subsequently before the VST was removed, some fuel seeped out either from the high pressure fuel filter or between the top and bottom of the VST
3) When removing fuel tube C from the VST a large amount of fuel exited, which I think was in the VST bowl?

? - Do I need to take the VST completely apart just to replace the grommet on the high pressure fuel pump?
? - Is it worth taking the VST apart and replacing all the gaskets? (I have all the gaskets)
? - any reason to test the high pressure fuel pump after removed from the VST?

Thanks Sam

Update:

VST rebuilt.
The new insulator (grommet) that fits on on the high pressure pump is a revision from the original. The new one has a hole about 30% larger and the length is about 3/8 to 1/2 " shorter.
Waiting on manifold gaskets then will re-assemble the rest of the motor parts removed to access the VST.

Sam

Update:
The needed parts came in and the motor is back together. I am happy to report that a test run on the ramp was successful. The motor was a bit sluggish for a few minutes and then ran very well.

Today I did a shakedown run for over 2.5 hours and the engine ran well.

I want to thank all those that took the time to comment and especially Alan Hicks for his important replies.

If anyone needs help with a BF40D, I will try to help. I would highly recommend purchasing the Shop Manual from Honda Marine. The book was invaluable in this repair.

Sam

As long as you were in there you should have replaced the pump. 40 to 41 PSI key one not running! 40 to 41 PSI when running! And not fluctuating when throttle opened. Should do a run text Honda says 1.2 oz in 2 second run. Run into a jar an collect the gas. Get a fuel pressure kit(Harbor Freight) hooks right up to the pressure release on the high pressure side next to high pressure fuel strainer. If that needle is jumping or below Honda's specs replace the pump. Do not try and use one of those $30 pumps from Amazon or Ebay. The ECU will cut it off after a one second run. Buy OEM. The el Cheapos pull to many amps and ECU shuts it down. The grommet or "insulator" swells over time and the seal is loosened up. Put the new grommet next to the old the difference in size is amazing. A friend and I both have 40BFDK2's (2014) Both pumps failed this year 2800 hours on mine, 1100 hours on his.