BF90 giving solid buzz when above idle

I have a BF90 on my pontoon with power trim and tilt/remote control. My BF90 gives the solid buzz and automatic throttle reduction that indicates I have an overheating or oil pressure problem. This happens as soon as I turn over the engine. I revved the motor in neutral, reverse or forward but received the same buzz. The weird thing is that I only get the alarm when the boat is in the water. If the boat is on muffs or a bucket, the alarm does not sound.

So far, I have:
1) replaced the impeller and surrounding seals.
2) replaced gear oil in lower unit
3) verified engine oil is near the top end of mark on dipstick
4) unplugging the Red and Yellow wires connection between sensors and CDI unit to disable both sensors
5) verified with an infrared thermometer that the temp of the engine is fine (still cold)
6) let the engine run at idle in the water for 5 minutes with no buzz

Nothing has worked so far. As soon as I try to rev the engine, the buzz returned.

I can stop the alarm from buzzing if I push the tilt down, but the alarm starts back up as soon as I release the lever.

I ordered a new thermostat, which should arrive today, but I can't see it being a temperature issue if the sensor is disabled. I also plan on taking my ohmmeter to test the CDI resistance per the service manual specs.

Is there anything else I am missing, which might cause the solid buzz when in the water above idle? I am hoping I do not have to replace the CDI, but will if the resistance test fails.

Thanks in advance for your help.

No good answers at this time....only questions...

What is the frame serial number of the engine?

Is this motor new to you?

If it is not new to you, did this start happening all of a sudden?

Do you have oil pressure and overheat warning lights? Are they on or off when the alarm sounds?

Do you have a shift box with key switch and warning lights built in? or Do you have a key switch panel separate from the shifter?

Is it a Honda shifter or is it possible that there was a Mercury or Evinrude installed before the Honda and the existing wiring was reused? If so, then, you probably do not have any warning lights.

If you do not have a Honda key switch panel or Honda shifter box with built in key switch and warning lights.....how many wires are going to the horn? This assumes that the warning horn is somewhere under the dash

If you do have a Honda shifter box with built in key switch, has anyone had it apart recently?

All of these questions may seem off the wall, but a lot depends on the vintage of the motor and the cabling, as to the possibliities.

Mike

Hondadude,

Thanks for your response.

Boat is on a storage lot, so the SN is not readily available. I will grab it next time I head over. I do know it is a 2005 bf90 outboard. It is on a Bentley Tritoon if that helps any.

I bought the used boat in October 2017. Took it out half a dozen times since then. Iirc, first few times I took it out, the buzzer came on when I was pulling away from the docks, but adjusting the tilt seemed to silence it. Would run after that with no problems. I believe the boat sat for a few years without use before I bought it. It is a work in progress, but his is a show stopper. My tilt and tachometer gauges do not work either. That will be my next thing to tackle.

The buzz started happening after I pulled in some sand after going into shallow water in the bay. Had to limp back to the docks after that with the buzz. This is when I replaced the impeller, cleaned out the area around the impeller, and changed the gear oil. The old impeller still looked good, but I already had it apart...

There are no warning lights that I can find.

I did swing by the storage lot and pulled the CDI today. After testing it’s resistance between posts, it appears the 9, 13 and 15 posts all come back with infinity to all posts, instead of proper resistance. Unless I am reading this chart wrong, I think the CDI is the culprit.

Would the CDI cause these problems?

The year of the motor most likely eliminates the retrofit from a previous Evinrude or Mercury Installation. The adapter used back in the day, many times would have issues internally, with broken or shorted wires.

Removing the yellow and red wires should indicate that the horn is being blown by something other than an overheat or oil pressure issue.

Since the power is being reduced, that means that the cdi thinks that there is an overheat or oil pressure issue.

It is possible that either the red or yellow leads have a ground on them....maybe melted to the powerhead. It would be worthwhile to check for any resistance to ground on those leads. Be sure to disconnect the cdi when doing your test.

To finally answer your question....yes, it could be the cdi. In the past 20 years or so, dealing with Hondas, I have never had the patience to go through the entire resistance test of a cdk....so I am not sure how valid the test is. If I can remember, in between things in the next couple of days, I will check the resistance on those pins on a cdi that I use for testing in my desk.

But....why did it suddenly happen after you hit the sand?

That is when I would check connections and wiring routing around the engine. I looked at the pin locations on the big round 14 pin connector, and all of the pins adjacent to the lead to the horn have positive voltage either constantly or at certain times like starting the engine....except one. That is the pin for the trim sender. That pin will vary from zero (ground) to 5 volts. The horn is looking for a ground (or zero) to operate. Could it be a coincidence that the alarm stops when you trim down? I don't know. It would be worth the time to pull the connector and plug apart and check for corrosion between pin 4 (horn lead) and 5 (trim sender lead).

Unfortunately, I could not explain why that would cause the motor to go into the limp home mode. So, we may just be back to the cdi.

....but why would the cdi go bad due to an impact????........as I scratch my head.

If you have access to another one from a friend's motor, it would be worth hooking it up.

Mike

I looked at a couple of different manuals and they all say that pin 9 should have an infinite reading. 13 and 15 have readings on some, but infinite on others.

Just looking at a few of the pins from 9, 13, 15 my readings do not agree with what the book says in about 50% of the time. I did get some readings from 9 that were supposed to be infinite.

Unless something happened to this CDI in my desk drawer, it has functioned as it should the last two times I used it to test.

So, as I mentioned before....I have not had success with this test.

Mike

Thanks for verifying the CDI test. I have the boat at the house today and am going through the wires. From what I see, 9 is for the tach. That might explain why the tach is not working, but should not throw the alarm. 13 and 15 are pulse generators, and the engine is running fine. I am now thinking it is not the CDI. I am trying to make a new friend who has a BF90, but not my main concern at the moment. I will continue to test the wires and see if there is a short somewhere. I will also pull the connector and plug and look for corrosion. I will repost once I am done testing.

frame serial number – BBBL-4700628

Looks like it was a short. That would also explain why it only happen when submerged. The previous owner performed some “wiring maintenance” and left a cable bare. Once I pulled that cable up above the waterline, the boat runs like new again.

Thanks for pointing me in the right direction. I owe you a dinner if you are ever in the Tampa area.