Honda BF90 O2 sensor fault

All,
I have a problem regarding my Honda BF90 that I hope someone can help me with. The engine has 260 Hrs use and 3 months ago after coming back to idle the engine light (PGM FI) and intermittent alarm would come on. The engine would still function fine, I would turn it off and on and the alarm would clear, 5 minutes later it is back on. Took it to my service rep and the code thrown was an O2 sensor fault, they changed the O2 sensor. Next trip it was back with the same fault and same code, they changed another O2 sensor. The fault once again was there on next trip, took it back and they found a corroded closed thermostat, they were confident this was the fix. Next trip, alarm again, and it is back at the dealer with the same fault code...O2 sensor. The dealer has said that the O2 sensor is actually working as advertised. On a side note a had to change the battery about 4 months ago and my old sounder used to alarm with low battery power. I havent yet checked the charge from the alternator but could low power be causing the ECM unit to throw an O2 sensor fault at idle. Hope someone has had a similar issue and can lead me right to the cause. cheers.

Low power can do many wacky things.

First the battery should have a capacity of at least 582 cca and 756 mca for the 90 HP injected models.

Make sure all battery connections are clean and tight (with a wrench). Should be fastened with hex nuts not wing nuts.

Make the motor is mounted high enough on the boat that the exhaust power on the back of the engine is at least 5.9 inches above the water line. This minimizes water intrusion when there are fast stops or you get hit by a wave. You did say it happened after you came to a stop. Was it a fast stop?

If the dealer used the HDS on it, they should have seen if the alternator was not putting out the correct voltage. The HDS does not test the quality of the battery.

The most common things that cause an O2 sensor alarm are:

-Faulty 02 sensor
-Water intrusion...which causes an O2 failure. Due to height of engine or how it is driven.
-High pressure fuel pressure not being in range. By this time you should have changed your high pressure fuel filter. A clogged filter can cause 02 failure.
-Faulty wiring to the O2 sensor
-Faulty ECU. Other than just a faulty ECU, the faulty battery might cause unusually consequences.

If it is back to the dealer, hopefully, they have contacted Honda to get some additional technical help. Did they check both thermostats? Yes, there are two in the 90. One for the head and one for the block. They are different temperature thermostats. As a side note, it is interesting that you did not get an overheat alerm if the thermostat was corroded closed. Most of the time, they are corroded open and the engine runs cold.

Hopefully, the dealer takes the boat out and runs it after their next effort. That is generally the only way to tell that it is fixed. It sounds like an unusual situation, and these kinds of problems are not ever intuitively clear. These are the kind that you hope that you just get lucky and stumble upon the answer.

Mike

Mike,
Thanks a heap for your response. The engine height has been checked and is all good, The issue with the bow wave after stopping hasn't happened as I have been careful to watch that. Apparently the fuel filter was changed during last service (11 Feb 11) I contacted the dealer today and they are only changing the O2 sensor (3rd one) again!!!! Water test tomorrow apparenty to see if fault will duplicate. Cheers mate.

Wade

The water test was carried out by the dealer, come up with no fault. I took the boat myself today and it alarmed about 10 times at idle. I was looking at some other parameters which I thought could contribute to the problem. The battery power is remaining pretty steady at 14.3 - 13.8 volts. I did notice at idle on the RPM gauge I was getting about 750 RPM, at this lower RPM it would alarm after about 1.5 minutes. I would play with the throttle and hold a higher idle RPM of 800-900RPM and it didnt alarm after waiting for about 5 minutes. What is the Honda advised rpm at idle for a BF90?. Could this low idle (if it is) be causing the low O2 sensor alarm to go into fault?

Idle speed in neutral is supposed to be 750 plus/minus 50. Sounds like it is where is should be.

Sounds like you need to take the ride with the dealer. I have done this many times until we could get it to fail. I let the customer drive, so I could observe if he was doing something inadvertently to cause the problem. He may be doing something incorrectly, or could be doing some things in a combination that I would not have thought to try. Either way, we generally get to the solution to the problem.

Mike
Mike

Well, I took the dealer mechanic for a run in the boat last Friday. They changed the inlet temp sensor and the ECU card, drove for an hour with no fault or alarm. Thought it was all good. Took the boat out again today for a fish and the same alarm is back at idle, there is no alarm whilst at speed or above 1000RPM, as soon as I come back to idle or troll the alarm will sound (engine light on, intermittent alarm, oil light green). I am now at a loss, so is the dealer. They have changed out O2 sensor X 4 times, ECU card, inlet temp sensor, HP fuel filter. I thought if it was a wiring issue it would also be sounding at other power settings not just idle. Can someone enlighten me, I am stuck and want to get this issue resolved. P.S they are reluctant to change the plugs as the engine is not missing at idle. Any thoughts???????

Very frustrating, I am sure. You can bet the dealer is frustrated too. Most likely, he has been talking to Honda about what to do. They make suggestions, he tries them. As long as Honda keeps giving him things to try, they will pay him for it. They are sometimes reluctant to pay for the boat rides etc...just depends on who they are working with. At least that is the way it works in the USA. Spark plugs normally are not covered under warranty, so if you think they should be changed, just do it yourself. Be sure to use the NGK brand when you do.

It sounds like you may not be in the US, but here, the District Service Rep, although traveling several states, are called in to address the unusual problems.

Have the codes that he found always been O2 sensor codes? Any thermostats changed yet? Easily done on this model 90.

Mike

Mike,
Thanks for the reply, the codes have always been the same, O2 sensor. They have also changed the thermostats. I will try and organise to get the boat back on the water for another test with the dealer to see where we go from here.

Wade

Hi,

I've been watching with interest as you try to sort out your 90 problem and a couple of things from my automotive repair background came to mind.

While I don't have much expertise with the larger outboards, I see some similarities with the newer fuel injected outboards and typical automotive problems.

One thing that caught my attention was that you recently replaced a battery. Also, you seem to relate the problem to engine rpm. Both of which (along with the mystery triggering of the O2 sensor code) made me think of alternator diode issues.

When diodes in the alternator fail, they can set up some RFI (radio frequency interference) because of the excessive ac current your charging system will experience. This is typically called "ac ripple" or just ripple. This "ripple" can play havoc with sensor values and Electronic Engine Control Modules. Below I have sent you a link to an article from Mercedes Benz on the subject. While it is not Honda specific, they all pretty much work the same way. I'm not saying this is your problem but it might be something to discuss with your repair shop.

http://www.pvv.org/~syljua/merc/TooSeptST07.pdf

One other thing that I have had strange experiences with on spark ignited engines is the knock sensor. I see that this outboard utilizes one. I have found that a faulty knock sensor can also cause problems for an engine's electrical system when it would seem totally unrelated. Simply unplugging the sensor while the "event" is occurring and operating the engine to see if the problem ceases is a valid troubleshooting technique.

Warning! Only do this with your dealership's blessing though! The knock sensor is there to prevent engine damage under certain operating conditions.

Just a couple of more ideas to throw in the mix. Good luck.

All,
The mechanic has now gone back to the drawing board and rechecked the engine height on the boat. They found it was sitting too low in the water, they have now lifted the height of the engine up, still requires a water test. I am still a bit dubious that this will fix the problem, as it has gone 230 Hours at the original height without an issue until now. Is there a logical explanation to this????????

Very possibly the bottom of the exhaust ports are very close or less than 5.9 inches from the water line. Your pictures did not show the top half and its relationship to water line.

Why everything was ok up until now? ....the technical answer may be "luck". Seriously, it is hard to tell.

Going back to basics sometime is not all bad and can generate new thoughts.

Mike

Thanks for the reply Mike. The dealer lifted the engine to correct height and I did a quick check on the spark plugs. All 3 were good appart from the lowest one, it had white powder all down the shaft and around the connector at the ceramic end. Changed all 4 spark plugs went out for a test run and didnt get an alarm. Dont know if the plug/connection was faulty or may it still be the wiring to that plug only time will tell ?????

Hopefully, you got the plug assembly cleaned out. Faulty wiring can do funny things. Keep us posted.

I assume you are in salt water. Check with your dealer for a recommended spray to minimize the salt problem. We do not have that problem here in the midwest, so other than using wd-40 to clean things up, we do not use much other than dialectric grease after that.

Mike

Mike

Hi All:

The problem is that you need to change your ECM too.

The new sensor is not recognized by the ECM.

I just change one on a bf225 and it was a warranty issue.

American Honda send me the kit with the sensor and the ECM.

Once you change the ECM and if in the future you have a o2 sensor
failure again the computer will recognized your new sensor.

As a matter fact new original sensor are diferents and thinner than the oldestones.

Hope you fix promptly this sensor heated the air that goes thru the manifold until

the combustion chamber.


Dr.Boat

All,
Took the boat out again second time after the engine was lifted, and it was alarming at idle the same as usual, at the time of alarm the boat was at idle and trolling with water being nowhere near the exhaust port. I have now been told that the O2 sensor was not changed since the last alarming issue. I have been told the O2 sensor is throwing a fault from the beginning, my question is if it throws a "fail code "does this indicate the O2 sensor has gone out of range and that is all or has it actually "FAILED" and needs replacement. I cant believe a system which seems so simple is so hard to troubleshoot, 6 months!! Any ideas??????

You said that the O2 sensor has been changed four times, is that correct? Or, as you indicate in your last post it wasn't changed as often as you had thought?

You didn't acknowledge my post about alternator ripple but I assure you that it is a valid suggestion. I'm no crackpot and am a performance rated, award winning automotive mechanic. And, with the old saw of "doing the same thing over and over and getting the same results" being the definition of insanity, then ideas such as the one I propose should not just be dismissed out of hand. I also have some other suggestions if that one doesn't work. Just let me know if you, or your mechanic, are interested.

If the shop you are working with won't investigate some "other" ideas or worse, is lying to you about what is being done, then there might not be much hope solving your issue without someone else actually looking at the problem.

I can confirm they have changed 4 O2 sensors. I did raise the question with them regarding the voltage, however, it was dismissed as they said the voltage range on the HDS was within spec for the alternator. 14.4 - 12.8v

Well, their answer confirms that they don't understand the concept.

I was asking you to ask them to check for ALTERNATING CURRENT RIPPLE or, to be exact, the presence of alternating current in what should be almost pure DIRECT CURRENT or rectified alternating current.

Voltage pretty much has nothing to do with the equation. If uncontrolled with a voltage regulator, your alternator is capable of easily producing 40 volts or more whether it be AC or DC current. The ALTERNATOR always produces ALTERNATING CURRENT as a matter of course when it generates the electricity to operate your boat. That's why they're called ALTERNATORS in the first place.

The point I was trying to make is that the components used to rectify the AC voltage that your alternator produces into the usable DC voltage that you need to charge your battery and run your engine frequently go bad and cause interference with other components in the form of RADIO FREQUENCY INTERFERENCE as a byproduct of the alternating current that "escapes" the charging system.

If these guys knew what it was and why it might be wise to test for it, it would, literally, take them no longer than 5 minutes using a Digital Multimeter. But, with the response that you got, I don't see that there is much hope of that. It falls under another old saying that goes; "a man hears what he wants to hear and disregards the rest". That can be harder to overcome than any mechanical problem.

All,
Still going with the original fault, still many times in and out of the workshop. Plugs have now been replaced along with fuel lines and LP filter. Problem still exists. Just to recap: The engine will sit a full RPM all day with no issues or alarms, as soon as it comes back to idle after about 5 minutes idling at approx 700 rpm on gauge it will go into alarm(O2 sensor fault). If i advance the throtlle to be in gear and trolling at minimum speed it will also alarm, as the idle rpm is still the same. Once i increase trolling speed to 1000rpm i can sit there all day with no alarm, as soon as i click it back to idle .......alarm. Any new thoughts apart from buying Suzuki or Yamaha!!!!!!. Also where I live there is only one Honda dealer and that is the only one i can deal with.

Wade,

If you are in the US, it sounds like it is time to call Honda Customer Relations to discuss your frustration. Maybe they will be able to get the District Service Manager in to check it out. Their number is
770-497-6400.

Mike

Agree with Mike. Time to "escalate" with Honda. They should want this problem solved and have the fix in their database. Their reputation is at stake on stuff like this.

Another slight twist to the alarm fault. The dealer has been good going back over everything and rechecking what has been done, they are still investigating at a higher level with Honda. In the interim as a temporary solution I have disconnected the speaker wire from the buzzer to give me some peace when fishing ( I still have the visual lights as alarm indication) I have gone out 5 times now, trolling, idling around, full speed, and not one single alarm. Yes the system still does work as i checked the wiring diagram to ensure the buzzer and lights werent in series. So how can disconnecting the buzzer stop the O2 sensor codes from coming up??? After those 5 times being out not once has it logged an O2 sensor fault alarm. I have also disconnected the O2 sensor while it was operating and the PGM light came to indicate a fault, that was to confirm the system still functions with the buzzer off. Any thoughts or similar instances with buzzers or wiring to the buzzers somehow going back to the ECM and throwing an O2 fault???

Dear Wade. Im following up on this old thread, as im experiencing similar alarm problems with my Honda BF90. Did you ever find a solution to your problem, and if so, what was the solution ?

Thanks

Danethor

Hello
I am a partner in a boat in Mexico we have a 2011 Honda 90 with about 400 hours on the engine. We are having the exact same problem with our engine.
We fish off the west coast of Mexico in a place called Barra de Navidad
This is my story about the alarm.
We were 10 miles from our Marina when I noticed water pouring out of the engine case.I pulled the cover off the motor and the bottom of the case was flooded with warm water the pee hole had water coming out of the back... I checked the oil in the engine it looked clean and the engine was running normal but water was coming from somewhere so we trolled back to the marina. I called the Honda mechanic and he had to take the cover off the leg and we found the tube that runs the P water had come off .OK here is where the plot thickens... Next time out fishing when we were out 15 miles right before we caught a big Marlin by the way. We had a check engine light alarm with a slow loud beep when we put the motor to idle.I turned the engine off and looked around the motor then turned it back on..it started with no alarm. Any way after that every time we put the boat to an idle or neutral the alarm went off. Yesterday we had the Mexican Honda mechanic come to check the boat..I asked before he came if he had a scanner to read the code that was giving us the alarm he said yes..(all conversations are in Spanish so a little can be lost in translation) anyway he showed up with out the scanner and had me turn on the engine and proceeded to check the oil in the motor as it was running. He showed me the dip stick and said the oil level was low and the oil viscosity was too thick and asked me if I was using Honda 10 30 oil? Unfortunately I don't do the maintenance on the boat my other partner does it and I could not answer his questions. It's funny in all my life I never saw anyone checking oil in an engine while it was running! He explained that an outboard motor was different from a car engine..while the engine was at idle we had about a 1/4 inch of oil on the dip stick .. he then had me rev the engine and he then checked the oil level and the dip stick was clean no oil! After that display we had him change the oil and filter with 5 quarts of Honda 10/30 ...now when he checked the oil level with the engine revved up it showed about 1/2 on the dip stick...He thought that maybe the thick oil and low oil level might be our alarm problem. After the oil change we went fishing... again out over 15 miles trolled around for over an hour idled the boat several times and no alarms ...We trolled back and about 5 miles from the marina we had another marlin strike which we lost after a brief fight...but while we were at Idle the damned alarm went on!! We will get the Honda guy to check the code but I'm willing to bet that it will be the H02 sensor...which I suspected was the problem after doing some research on it..I suspected that because of the water we had enter the engine compartment when the pee tube came off.
I would sure appreciate any constructive comments on this problem and on checking the oil level while the engine is running.
Thanks in advance ...oldgringo

Danethor, did you find a solution or get a response from Wade, I have same problem also.
Thanks

I have the same problem too, waiting for high pressure fuel cable to test. I have thread started too.

RoyH said:

Danethor, did you find a solution or get a response from Wade, I have same problem also.
Thanks

Click to expand...

I have been following this thread for over a year and never read the solution.. i have the same problem. Wondering if i should start another thread to re-gain attention from other users with new experiences.

I have changed thermostats, o2 sensors, map sensor, valve seals, sparks, and fuel filter and same alarm.

The last guy who took a look at it said that the rpms at idle where under 700.. around 650 so it felt extremly rough. and thats when my buzzer comes on.... he said that my throttle cables where too short to adjust it. i will try with a different throttle cable later this week or the next one. I read somewhere that someone had also rpms close to 750 and the motor run rough.... any thoughts?