Df115 trouble shooting rpm/ fuel issue

[kurttruk]

I can run for a bout 5 to 10 minutes untill my engine starts to bog down and will only make 3000rpms. Changed fuel filters a few times. Each time it would work again then 5 to 10 minutes later it would do the same thing. The fuel is good. Could the high pressure fuel pump cause this? Or maybe the engine heating up cause this? any ideas? maybe the neutral sensor acting up?

[Swanie1975]

I have a df140 which has done this exact same thing to me on 3 separate occasions. After being out for a while with no issues I will start up and go to put the throttle forward and she will only rev to 3000 and feel sluggish. each time i have simply stopped, turned off the motor, restarted and away it goes to Wot without any further issues.
I recently had the primer bulb collapse which stopped the motor dead and I was towed in. Since the repair I haven't done enough hours to see if this has fixed the issue with the rev limit.

It will be interesting to see how you go with your issue as you are not the only one with it.

Ps motor was all new with lines etc in 2011 so I wouldn't of thought the bulb would collapse within 18 months.

Cheers Ryan

[nelbur]

It sounds like you may have a plugged vent fitting causing a vacuum to develop in the fuel tank. This would starve the engine of fuel and would cause the bulb to collapse. Opening the fuel cap should eliminate the vacuum and correct the running , IF a plugged vent is the problem.

[Moonlighter]

I have the same problem with my DF115 (2009) model.

My Suzuki mechanic and I Thought we had it beaten when he fitted a new fuel regulator. But it has now started happening again.

I am beginning to think there may well be something in the suggestion of a intermittent fault in the neutral throttle sensor or the associated wiring. Having read up a bit, this sensor when activated prevents the engine revving more than 3000rpm and limits the spark advance to 9 degrees, resulting in sluggish acceleration. Which is exactly how it feels when my engine plays up. It is exactly like the engines ECU thinks that the engine is in neutral.

Will be talking to my mechanic after the Christmas holidays and will be suggesting that we change this sensor and see if the problem disappears.

Kurt - if you have any luck resolving this problem in the meantime, please post here and share your solution! I will post again if we solve it on my motor as well.

Thanks!

ML

[DeeFour]

I have also the same issue in my DF140. Motor is 2007 model with around 400 hours on it.

I have a df140 which has done this exact same thing to me on 3 separate occasions. After being out for a while with no issues I will start up and go to put the throttle forward and she will only rev to 3000 and feel sluggish. each time i have simply stopped, turned off the motor, restarted and away it goes to Wot without any further issues.

This is exactly the same what has happen three times with my engine, I guess it has happen around once per year or something like that. It is no big problem, because I can always stop and start the engine and after that it runs really strong. Anyway, I like to know what is real reason for this problem? I am sure it has nothing to with gas or vacuum in gas tank. Also, no alarms or fault codes.

One Suzuki mechanic think it may be a drop of water in the fuel. A small amount of water goes to one injector and prevent gasoline injection for one sylinder for some reason. When the engine is re-started, it pressurized the fuel line and the injector with drop of water spit water out when the injector is opened at the first time after start and after that it runs like it should be. I guess this theory make sense, but it is only speculation what may has happen. However, I have not found any water from my water/fuel separator nor gas tank and I have start to doubt is the water in fuel real root cause.

[Moonlighter]

Dee

Thanks for that info.

When the problem occurs on my boat, it seems to happen several times on the same trip.

I often travel about 50 minutes to the fishing grounds, then stop and drift for say 5 or 10 minutes, then start the engine, move back to the beginning of the drift line, and repeat that many times during the day.

So we might stop and start the engine 20 to 30 times in the day. It can happen several times during the day, we finish a drift, start the engine and try to get onto the plane to go about a mile or so to start a new drift. Sometimes it is fine, other times it wont rev past 3000 rpm, but when it does that, we simplystop, turn the engine off, wait a few seconds, restart and it goes as good as new!

Very baffling. Tried shifting it from forward to reverse and back again with the engine still running, but it makes no difference. Have to turn off and restart before it rectifies itself.

Cheers

ML

[kurttruk]

Dee

Thanks for that info.

When the problem occurs on my boat, it seems to happen several times on the same trip.

I often travel about 50 minutes to the fishing grounds, then stop and drift for say 5 or 10 minutes, then start the engine, move back to the beginning of the drift line, and repeat that many times during the day.

So we might stop and start the engine 20 to 30 times in the day. It can happen several times during the day, we finish a drift, start the engine and try to get onto the plane to go about a mile or so to start a new drift. Sometimes it is fine, other times it wont rev past 3000 rpm, but when it does that, we simplystop, turn the engine off, wait a few seconds, restart and it goes as good as new!

Very baffling. Tried shifting it from forward to reverse and back again with the engine still running, but it makes no difference. Have to turn off and restart before it rectifies itself.

Cheers

ML

Ive been pretty busy with school so i havent done much trouble shooting. I have elminated the fuel vent and the boat fuel system. As for the motor I will try a few thing as I have twin df115's on the boat so ill start swaping parts from one to the other till I can get the problem to go away or duplicate on the good motor. Thinking I might swap the mass airflow sensor to start and go from there.

[Moonlighter]

Ive been pretty busy with school so i havent done much trouble shooting. I have elminated the fuel vent and the boat fuel system. As for the motor I will try a few thing as I have twin df115's on the boat so ill start swaping parts from one to the other till I can get the problem to go away or duplicate on the good motor. Thinking I might swap the mass airflow sensor to start and go from there.

While you are swapping things, could you try the neutral theottle switch on the engine please! I think it is a pretty easy thing to remove and replace, maybe 20 minutes to do each.

The more i think about it, the more i am becoming convinced that this switch could well be the culprit! Sometimes we might look at more complicated things when the simple little parts like this could be the solution right under our noses....

Regards

Grant

[noelm007]

remember there is 2 neutral switches, one on the motor, and one in the control box, I do believe that they are connected (in a strange sort of way) via the wiring loom.

[Moonlighter]

Hi Noel

Yep, aware of the two switches. If the one on the control box is faulty, the engine simply wont start because its the n-gear protection.

It is the one on the engine that causes the ecu to limit the throttle to about 3000rpm, and restricts advance, fuel delivery etc.

Which is exactly how it "feels" through the throttle when my engine misbehaves as described earlier. Doughy acceleration, lack of the normal full throttle range, but otherwise runs fine. Hence i am pointing the finger of guilt at a intermittently faulty neutral throttle switch or related electrical connector/wire/plug or something. Either that or the ecu has a intermittent glitch....

Grant

[WEDOCQ]

Grant,
The nuetral safety switch in the engine area is a common issue. I had to replace mine, but not for the reasons you guys are suggesting. Mine would not allow the motor to even turn over if it wasn't activated (button pushed in while the linkage was in nuetral). It's relatively inexpensive and easy to replace. I will follow this thread to see if that was your problem.
-Shawn

[kurttruk]

Just an update. Ive been busy with other things but did try and run the bad motor/side on an external fuel tank. Problem disapeared. So from the suzuki fuel filter/ racor back to the fuel tank is where the problem is. I am questioning the pressure relief valve on the top of the racor/suzuki/ fuel filter. If the valve is stuck open leting air into the fuel system could that cuase this issue?

[Harper]

No "pressure relief valve" system on any fuel filter is going to vent or release pressure to the atmosphere. It simply is not open to the air at all, so there is no way that any malfunctioning fuel filter relief valve can let air into the system. If you filter is clogged or there is some other sort of obstruction in the fuel delivery system, and if the relief valve (or bypass valve) is stuck closed, it would surely cause a problem. Actually, I'm not really following what you mean by a "pressure relief valve" since the Racor filter position that I think you're referring to would be on the suction side of any fuel pump on your outboard. And if that is what you mean, then the bypass valve would route fuel around a clogged filter, but still wouldn't suck air. If I'm mistaken about which filter you're referencing, there is still no place in the delivery system that allows exposure to the atmosphere, unless there is a leak or a broken component.

[pelermon]

Just an update. Ive been busy with other things but did try and run the bad motor/side on an external fuel tank. Problem disapeared. So from the suzuki fuel filter/ racor back to the fuel tank is where the problem is. I am questioning the pressure relief valve on the top of the racor/suzuki/ fuel filter. If the valve is stuck open leting air into the fuel system could that cuase this issue?

3000 rpm is the rev limiter - Your neutral switch is probably faulty, telling your engine it is in neutral full time, - It may temperately work and not - Sounds like you need to replace it soon.

[Moonlighter]

Ive spoke again to my mechanic and he is still convinced that it is a fuel system problem.

So, We have fitted 2 non-return valves in the fuel lines, one right back at the tank outlet, and one between the primer bulb and the engine.

Immediately noticed how much quicker the fuel bulb pumped up hard, and it has stayed firmer than it ever has before. Promising.

Due to the extremely windy, rainy weather and storms and floods here, have only had the boat on the water once for a quick 15 min run after installing the above. No dramas. Went fine. But really need a couple of full days on the water to know if problem solved or not. Will keep you all posted on developments.