honda BF90D surging in mid RPMs

[ssobol]

I have a 22 cruiser with a 2008 Honda BF90D on it. When the engine is running slow <1200-1500 rpm it runs fine. Between ~2000 and 4000 rpm the engine will not maintain a steady rpm. It will drop a couple of hundred rpm for a second, recover, then drop again. It will keep doing this continously and it is pretty annoying. Once the rpm is above 4100 or so the engine runs smoothly. I was out for 3 hours today and the engine operated consistently throughout.

It operates the same on either tanks. The fuel in the tanks is from different sources and was purchased at different times.

Any ideas would be helpful. Thanks.

[Mike B]

I have been having the same problem with my 2007 honda 90. Mine started between 3700 and 4000 rpm but towards the end of the season it would get bad starting as low as 2K. Problem will dissapear if I bring up the rpms or after it warms up at cruising speed. Im sure my gas is good and all filters ar new. All research I do says the older carb models had a similar problem, but no info to be found about EFI engines. I will be looking for an answer along with you, the nearest Honda dealer isnt close to me at all. Good luck

[Discovery]

I have had the same experience with the Stb. Honda 135. Never has happened with the port motor. Usually occurs at 3800 RPM.

[Pandy Girl]

I had the same problem about 1800 to 2000 RPMs, Took it to a Dealer he said the Carbs needed Cleaning out. I left eth. Gas in it about 6 weeks without any additives. The Dealer cleaned the Carbs. very good. That has been about 200 Hrs. ago. Runs great now Jim (2007 Carb. Engine Honda)

[potter water]

Just another possibility, as I've experienced on several small EFI engines.

A major input to the computer to adjust timing over the rpm range is a throttle position sensor. It tells the computer where the throttle is, obviously. They are normally a mechanical potentiometer that varies resistance as the throttle moves. It is a critical component in most modern EFI engines, though I can't guarantee that is the case with outboards. Most outboards from Japan are modified car engine or directly taken from those designs.

Those potentiometers, being mechanical are a bit of a weak link for being so critical to engine operation and they do go out. They get dirty or slip adjustment. And their failure WILL cause the symptoms you've all described.

I had a major battle with my dodge truck mechanic with an intermittent jerk and jolt when I had the pedal depressed to the same spot. He fought hard that it was an O2 sensor, but I finally, after three trips to the dodge garage, I told him to replace the TPS anyway. No more problems fro the rest of the time I had the truck.

Just a thought.

[Mike B]

Let me run this by you please. My boat is put away and I dont know enough about the engine to picture what Im going to say without seeing it. You may know the answer. Thes past season I had that problem with a plastic T-stat cover leaking. And it was leaking real good, so good fuses were shorting/corroding and blowing. After I straightened that mess out I wondered what else could have been damaged that I wouldnt catch until later. Since the TPS is mechanical, is it possible it could be hurt from salt water leaking from the T-stat problem ? thanks, Mike B.

[Les Lampman]

Hi,

I'd like to add to the conversation here. Please understand that I am a Honda dealer and do feel like I need to be sensitive to that fact and somewhat politically correct. In other words, I'd like to tell you what I think is going on but I'm hoping it doesn't result in a rush to Honda dealers and Honda Customer Service. I'm walking a narrow path here in trying to help without causing issues.

The Honda BF90D (EFI engine) has a bunch of stuff going on in the ECU (Electronic Control Unit). It's programmed for BLAST, for Lean Burn, and for V-TEC (variable valve timing). BLAST senses how quickly the throttle is moved and adjusts the timing for more reponse if it senses a quick demand for power. The Lean Burn technology operates between 2,000 and 4,000 rpm. When the engine is operating in a steady state, and within certain parameters, the ECU will attempt to lean out the engine as much as possible for better fuel ecnomy. V-TEC happens at 5,250 rpm and literally changes the cam lobe the rockers are following to a high-duration, high-lift profile for power.

I had issue with the first of the BF90D engines in trying to get them to "settle down" in the Lean Burn range. Power application was very erratic at the 2,000 rpm and 4,000 rpm mark in particular and not particularly stable within the 2,000 to 4,000 rpm range. I had a Honda engineer out here to check what was going on when we complained bitterly about the first few BF90D engines. The engineer found that the spark advance was changing in ways it shouldn't when moving into and out of the Lean Burn range. I proposed that is was due to the nature of the CD22 hull shape and its (rather) unique power requirements (when compared to more typical hull types) and that the ECU was having trouble "sensing" the load on the engine and when (or when not) to utilize Lean Burn. This resulted in very rough (really, jerky) operation.

Honda did more testing at their facility in Florida and was able to replicate the problem. Subsequently they worked with engineers in Japan to change the programming in the ECU. We replaced the early ECU's and found the new programming to be much better. The ECU also "learns" the typical operation of the boat over time so oft times things improved even further with use.

I've found, repeatedly, on lightly loaded boats (not lightly loaded C-Dory boats but boat that don't demand a lot from the engine like the C-Dory) that it's difficult to get a BF90D to run absolutely smoothly. Or I should say "all" BF90s, for some reason some do run quite nicely. Most seem to have a stumble or surge around 2,000 and around 4,000 where the Lean Burn comes in and goes out (respectively).

In trying to help in this one case I'm afraid of having everyone with a BF90D start wondering about theirs. Keep in mind it was only a very few early BF90Ds that had the initial issue and that stumbling (or surging or hunting) is usually mild and that there are still very good things about the engine that make it worth having even if it stumbles a bit (this isn't unique to the BF90D, I've had $25,000, highly engineered, top-of-the-line motorcycles exhibit the same issues; bikes from a highly regarded German maker that really shouldn't surge...but do).

If you have an issue like this with your BF90D you'll have to make some choices. It is (or can be) annoying and it probably shouldn't really happen but it does sometimes but it won't damage the engine or leave you stranded. You'll need to decide how far to push it (if at all) with your Honda dealer and whether or not it's worth the effort. I can tell you if Honda gets a dozen calls on Monday morning saying they heard from a dealer up in Washington that they might have an issue with the ECU, Honda is not going to be very happy with me at all. I'd encourage you analyze your own personal situation and determine if the level of the (potential) issue is worth the pursuit of a (potential) resolution. If you have a very early BF90D with a very pronounced surge or stumble I might suggest following it up. If you have a later engine and just some stumbles around 2,000 and 4,000 you might decide that, while not ideal, it's fine as long as you know your engine isn't being damaged and you won't be stranded.

Hope this helps out a bit.

[Captains Cat]

Great Explanation as usual Les. Thank you very much!

Charlie

[ssobol]

Les, your explanation makes some sense.

I am glad that this issue does not indicate pending failure of the engine. However, it does make the boat ride annoying with the boat constantly speeding up and slowing down when the engine is operating in this range.

However, what can be done to correct this issue? If I raise this issue with Honda what is likely to be their response?

[ssobol]

If my engine is still under warranty is this something that is covered, or does Honda just say that's the way it works?

[Captains Cat]

I'd call and ask them soon, it's good for FIVE YEARS and with a 2008 engine, you're getting close to the end...

And don't blow the whistle on Les!

Charlie

[ssobol]

If the engine was originally purchased before July 1, 2008 the warranty is for 3 years. If it was purchased after July 1, 2008 the warranty is 5 years. I am the second owner of this motor, so I am trying to find out when it was originally purchased.

The warranty will transfer with the ownership of the motor if it is still in effect.

[ssobol]

In mid December I took my CD-22 to the nearest Honda Service Center. Since it was the week before Xmas and then they were closed between Xmas and New Year's they didn't look at it until January.

After they ran the engine, they said that yes indeed it was surging. Surging is probably not the correct term. What actually happens is the engine RPM drops a couple of hundred for a split second and then recovers. Going at 3600 rpm and about 20 mph and having this happen constantly is really annoying. Go to 402 RPM (on the gauge) and this stops immediately. I haven't felt it do this at low RPM (e.g. 1200).

The service center said that there was a service bulletin on the fuel system that was supposed to address the issue. It involved replacing a number of parts in the low pressure fuel system. It took them some time to get these parts. After complying with the SB the engine still surged. Then they said that it might be the filter in the vapor separator, so they replaced that. Engine still surges.

In late January I went to see what was up (this was when they told me they were waiting on parts). I talked to the tech and mentioned that maybe there was an issue with the ECU. They said that if the ECU was causing the RPM drop because it was switching cams, the ECU scan would indicate this, but it does not.

I last talked to them about 10 days ago. They say that the engine still surges and that they are in contact with Honda about it. They told me there was a number of tests that Honda wanted them to do and report the results.

They did ask me if the engine had been damaged. They said a possibility was that a rod was bent. I'm not aware of any damage to the engine. I would think that if a rod was bent the engine would run much worse than it does (it runs fine at idle and above 4000 RPM to WOT).

I understand that this has taken awhile because not only waiting on Honda and parts, there have been reduced opportunities for them to test the engine due to it being winter in DC. However, boating season is fast approaching and I want to get this problem sorted out.

I am traveling on business right now. Before I left I called the service center and said I would be away for awhile and was it ok to leave the boat there. The fact that they said "Sure, it'll be no problem to leave your boat with us while you are gone" kind of gives me the impression that a fix is not imminent.

The only good thing about this is that I've gotten free storage for the winter.

[ssobol]

Finally got my boat back. Granted it has been winter here and the service center had intervals where they could not run the boat because of the weather to test any fixes on it.

Basically the problem was the ECM. It was replaced under warranty. However, it took Honda quite awhile to be convinced of this. The service center would talk to Honda and Honda would tell them to do this and check that to see what the problem was. It went back and forth for awhile. Finally, Honda agreed to change the ECM and the problem was solved. I did find online a Service Bulletin (#61) that describes and addresses this problem with a replacement ECM. The SB was released in late '07 for the BF75D and BF90D engine. Apparently there was a problem with the way the previous ECM was programmed to handle the air/fuel mixture.

Anyway it's all fixed now and the motor runs fine.

[potter water]

I'm betting they replaced the TPS somewhere along the way and that was the real problem. But, the good news is you are back in business.