DF300AP RMP Fluctuations??

[Jakess]

I have a 2015 300 zuk on a 23ft Albury Brothers. Great setup and really like everything about it except periodic RPM fluctuations for no reason. I ran the boat on mother's day and after 45 minutes cruising at 4200 RPMs the RPMs went from 4200 up to 4400 down to 4050 back up to 4400. It continued until I slowed down. This happens for no reason at all. It will happen in no wake zones or during a 4 hour boat trip. The first time it happened I was walking around cleaning the boat and I could feel it speed up. I looked at my son to see if he was doing it and he was not touching the throttle. I have had other Zuk owners drive it and they tell me that they have never felt anything like that on their boats. One comment was "that is not right". It does not happen everytime I take it out. I have had my certified mechanic look at it on four visits. He told me the rep looked at it and said it is just what happens with he eco boost. I cannot accept this as the answer. I want to cross the Bahamas this summer but I cannot with this issue. Has anyone had this issue? Any idea? I feel like it is a computer issue but there is too much technology in these new engines for me to diagnose.
I have video of it on two different occasions. Thanks for any feedback you can provide.

[Moonlighter]

I can't say that I have heard of that before. It does not sound right at all.

A decent prcentage of issues we see reported here on the forum end up being:

- due to a poor 12 volt system on the boat - a bad battery, loose or corroded battery terminal connection, corrosion inside a main battery cable or inside the mian battery switch, a bad earth on the motor, dirty main fuse connection, or a poor "white wire" condition or connection or something similar. All modern EFi 4 strokes demand a good power supply, and the Suzukis dont like poor or variable 12v either. They can do truly strange things when they dont get it!! So suggest you thoroughly check all components in your 12v boat system such as those mentioned earlier. By check, I mean undo connections, verify wiring connectors are good, clean, and then reconnect. Grease if appropriate.

- fuel supply related - such as water or other debris contaminating the fuel system, partially blocked or closed fuel tank breathers (mud wasps like to build nests in the outlet), failing anti-syphon valves on tanks, stale fuel, fuel lines breaking down internally and restricting fuel flow, air getting into fuel lines at joints etc. So, check all of that out thoroughly. Undo and blow thru the breather line to make crtain it is clear. Get rid of the anti-syphon valve, it is just a problem waiting to happen IMO. Give fuel lines a flex to ensure they are still supple, any that have crunchy feelings or hardness and wont flex should be replaced. Replace external fuel filters and when you remove them, tip the contents into a glass jar let it settle and see what you find. If you find any evidence of water or contamination, you have more work to do to get it out of the tank and figure out how it got in there in the first place.

All of this really falls into good maintenance practices, so even if it doesnt solve the problem, it is worth doing anyway and at least eliminates those possible causes, so the mechanic can focus on other more complex issues.

If you do all the above miantenance and the Suzuki mechanic still cant figure it out, get them to talk to Suzuki HO and technical support - show them your videos is a great idea and proves that there is a real issue.

Hope this helps. Let us know how you go and if you find a solution.

[white diamond]

My 2016 300 does the same thing in the ocean with waves and swell. My mechanic said it is normal and caused by the lean burn system. It does not fluctuate in calm waters in the sound. I am getting more use to it now but was really annoying at first after upgrading from a 2004 DF250.

[white diamond]

The mechanics explanation seemed logical. He said the lean burn system was trying to maintain the best fuel mileage with waves & swell. It fluctuates less if the sea condition allows me to increase my cruising speed.

[Moonlighter]

I have several friends who have various hp engines with Suzuki lean burn.

None of their engines do this.

I have sent a Q on this to my local Suzuki technical expert. Will let you know what he says.

[Moonlighter]

My Suzuki tech guru (certified Suzuki Master Tech) says

"This is not normal. Possibily - without being able to see it and test - the O2 sensor may be on its way out".

If you search posts on this forum, you will see there were some issues with O2 sensors on some earlier AP series engines. A new design O2 sensor is available when any are replaced due to issues.

[Hawthorne]

I have the exact same behaviour on my DF250AP (2014). The boat is new (to me), and I noticed this on recent trips when RPM is set around 4000.

Please update this thread, if you (your dealer) solve the problem.

[Bamahemi]

I have a 300 '14 model and it does it at troll speeds and seems to be associated with resistance on boat from the current. Went to Tortugas last May no issues. Mpg hand calculated at 3.42 mpg, probably more to do with 8 knots for 40 miles on way back in 6-10s! I'm happy with mine. I did have the 02 sensor replaced around 50 hour mark and no change in behavior. It's weird sometimes but not an issue. Motor runs perfect in my book, these things have all kinds of sensors monitoring and changing for efficiency. Yours jumping huge amounts of rpm might be an issue, mine is more subtle.

[ChrigelKarrer]

I have 3 DF300AP,
one 2013 and twin 2016 and none of this does this and never done it.
As the digital trottle synch system will keep the RPM synched the RPM should not fluctuate.
The only thing i can immagine is that your speed at 4200 rpm is jus a tad too low to keep your boat planing,
so it continues to slow down and go faster with the wave/current action.

What propeller are you running and what is WOT speed and rpm?

Chris

[redlowrey]

I have 3 DF300AP,
one 2013 and twin 2016 and none of this does this and never done it.
As the digital trottle synch system will keep the RPM synched the RPM should not fluctuate.
The only thing i can immagine is that your speed at 4200 rpm is jus a tad too low to keep your boat planing,
so it continues to slow down and go faster with the wave/current action.

What propeller are you running and what is WOT speed and rpm?

Chris

''''''' That sounds more like what the problem is, Suzuki have got them selves in more trouble then the early settlers with this one. The only place that you could run a lean burn would be in a lake or an ocean with a flat sea, ie no swell, no current or wind.
That would let the 02sensor cycle and keep the air fuel ratio at stioch, 14.7 to 1. While you are cruising in lean burn the map sensor signal voltage will remain at a constant value, the moment you hit a wave the rpm will drop, map sensor signal voltage will head towards four volts, and pulse width on the injectors will increase and the ecu come out of lean burn. So there will only be certain conditions where the engine will run in lean burn.

[bassyac]

That's some answer. My 300AP has had some RPM changes but I only noticed it in 4-5 foot waves, not so much on a nice flat day. Don't have many of them though. I just thought that it was the prop getting a better bite then getting some air or my shaky hand on the throttle. It mostly happens in that 3800-4200 range, around 34mph.

[Jakess]

Went out the country sorry for the delayed response. Thank you for all the thoughts. I am a fanatic about maintenance. All done by the book by a suzuki authorized mechanic. I only use non-ethical fuel. I use a racor filter so i can see if there is any water in fuel. To moonlighter's point, I did have O2 sensor issues. It was replaced under warranty six months after I bought the boat. Now that I think of it, that could have been when this started. I use odyssey batteries (4), could this be the issue? I also use the the Stealth charging system. Could this be the issue? I have called the manufacturer of the boat and he told me that no one has called with this issue. He puts my set up on a number of boats. The fluctuations happen almost every time I go out. I do not go offshore that much. I mainly stay inside and mostly in the ICW and the St John's River (Jax Fl).

[Jakess]

Still having the problem. Got ahold of a top person at Suzuki, explained the issue. He asked that I sent a video and never heard back. Went dark. I have it back to the shop and asked them again to check it. For some reason, I am thinking could be in the electric throttle. Anyone have any issues since I last posted?

[henpecked]

I have had the same issue - both with twin 2008 300s [installed new on the boat in 2008]; and with brand new 2017 twin 300s just installed as a repower. It does seem to occur in rougher seas running offshore, particularly a steep headsea. Only suggestion from the local mechanic was to replace control box/ecm/etc. which I will probably do now that the offseason is upon us. I too would appreciate any updates as it's been a mystery for me for some years. Doesn't seem to impact the performance of the motors per se, just more of an aggravation, if you will. cheer!

[Jakess]

I tend to go offshore only on calm days. It happens to me on flat calm water as well as rough seas. Since it is easier to feel on calm water, I notice it more. I want to cross to the Bahamas but until I understand the issue, I do not have a whole lot of confidence.