04' DF250 3800 RPM then drops off

[miragedsl]

I'm working on my buddies Motor for him. The boat has been sitting for about two years not used. The engine has 115 hours on it. When he was using it he religiously used staBill fuel additive for ethanol. I removed all of the old fuel and replaced the racor fuel water separator. After fixing other items not related to the engine I took the boat out for a test run today. The engine started out fine with no issues. I was originally running the boat at 3500 RPM without any issues when I tried to go past 3800 RPM, The RPM started to drop off and become erratic. I throttled back until the engine settled out and then tried to advance again and it would run to 3700 rpm before dropping off again. It ran at 3700 RPM for several minutes but then it started do the same thing it did at 3800 RPM. After going through a few evolutions of the same issue it eventually would not go higher than 3500 RPM without becoming erratic and dropping off. The engine never stalled or was hard to start. There were never any beep or buzzer alerts or flashing codes from the tach. I know none of the onboard fuel filters have been replaced or onboard fuel hoses. The fuel priming bulb has also not been replaced. Any advice you can give me would be very appreciated.

[Harper]

Sounds like fuel starvation. When it does it again, check the primer bulb to see if it is collapsing, indicating a problem with venting or with the anti-siphon valve at the tank. Also could be the fuel line itself that is soft and is collapsing with higher fuel demand.

[Solarman]

Mike there is a shift sensor that limits motor to around 3500RPMs, this is not the neutral sensor.

Good luck.

[Harper]

Mike there is a shift sensor that limits motor to around 3500RPMs, this is not the neutral sensor.

Good luck.

Yep.......

[miragedsl]

sensor test

would this sensor have a trouble code if it was malfunctioning? is there a diag. test for this sensor? my first thought is fuel delivery, but it seems like there are a lot of parts that can cause this. i read the post about 4k rpm issue and it seems similar in that the same parts could be at fault. i'll start at the tank and work forward.

[Moonlighter]

would this sensor have a trouble code if it was malfunctioning? is there a diag. test for this sensor? my first thought is fuel delivery, but it seems like there are a lot of parts that can cause this. i read the post about 4k rpm issue and it seems similar in that the same parts could be at fault. i'll start at the tank and work forward.

No it won't throw a code because it's a normal engine function for the neutral throttle switch.

There is often some confusion about these switches.

My understanding is that are 2 switches affecting the engine starting and running in neutral.

One, in the binnacle, prevents the engine from being started unless it is in neutral.

The other, in the engine, prevents the engine from being revved excessively when it is in neutral. It is possible this switch is not working properly either due to being loose or faulty. Worth checking.

It's also possible that you have a low voltage situation. These engines are very voltage sensitive. Any poor battery connections, corrosion in cables, or bad connection of the White wire that powers the ECU can cause these kinds of problems. Check everything in that regard. And by "check", it means disconnecting battery cables or other connections, clean, lubricate and replace so that you are 100% certain that there are good contacts.

[miragedsl]

I had not thought about the voltage. Thanks again.

[redlowrey]

The engine neutral switch limits the rpm to around 3000 and keeps the timing to 8 degrees, it sounds like your running out of fuel, start with changing all the fuel filters. The neutral switch will be closed in neutral and open when in gear easy to test with a test light.

[aubrox]

Hi I've just enter this forum and don't really know how to exactly use this page...

My main problem is I just recently import a boat I ordered the twin Suzuki DF300AP lean burn model 2015,still doing the engine braking both have 5.5 hours on the clock...I started both engine this morning at about 5 min I heard an annoying buzz sound, I check on both tachometer it say Check engine code 3-6 with later after some research I found out it is the O2 sensor...Can someone please explain what cause both engine to send the faulty alarm at the same time and how to fix it too


Thank you looking for some reply ASAP

[Moonlighter]

I have read that Suzuki did a recall on the O2 sensors in those engines. Best to contact your dealer regarding this.