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Seems a fairly common problem on the forum but really no answers . Cant seem to raise revs above 4000 on DF250 . No warnings and all seems fine , no noise or vibration up to 4000 revs . Try to raise revs and no response . Anyone any ideas ?
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It is hard to diagnose problems from a keyboard but what I would suspect could be the problem is a faulty fuel pressure regulator. At higher rpm's this device is supposed deliver a higher pressure from the high pressure fuel pump to the injectors. This is a pop off design that bleeds off excess pressure to the vapor separator tank (a small gas tank that holds the high pressure fuel pump). This happens when you cut the throttle to idle and the pulse width to the injectors is reduce so they are spitting ( and need less gas). At 38 psi the pressure regulator valve bleeds off the pressure. As you throttle up the injectors need more gas so the pressure needs to be increased so the bleed valve shuts down.
If the regulator continues to bleed the pressure off at higher rpm's the engine is starved for gas (leans out).
Another scenario involves the float, needle valve assembly in the fuel vapor separator. This is a mini fuel tank that holds a few oz of gas to feed the high pressure fuel pump to the injectors. This designs defeats the great strides that fuel injection has over come vis-a-vis with carburetors. The float needle could get cruded up with dried gas and reduce the amount of gas going to the separator tank. At low speed this is not a problem but at high speed you can start sucking air which will cause you to lose power. In both cases you suffer from reduced cylinder pressure so the engine cannot continue to accelerate.
To complicate things either scenario will not necessarily throw a trouble code to help you to determine the fault. These devices are not connected to the ecm because they are analog devices. They may trigger a non specific fault, bu that doesn't really help.
There could be one more issue but this would trigger a trouble code on the ecm. What controls demand on an injected system is the Map sensor (manifold absolute pressure). The ecm scans for variations in pressure and maintains a fuel strategy for how long to turn on the injectors to maintain a certain air fuel mixture for a given throttle opening (and vacuum pressure).
Usually they are attached to the manifold with a hose and clamps. Hoses can crack and rot providing an air leak which can throw the ecm calculations off.
It could also be plugged up with carbon or fuel and could prevent it from changing pressure. At wide throttle openings the vacuum pressure is low because a lot of air is coming in so the ecm knows it has to throw down a bunch of gas to keep the mixture trimmed to the right ratio.
There are a host of other issues that could also give you a similar result but these would be my prime suspects. The others would result in an engine that does not run well at lower speeds (rough idle, misfiring). Yours seem specific to a certain rpm.
With all that said it could be something as silly as a clogged vent on the tank, faulty primer bulb, clogged fuel filters or a faulty low pressure pump. -
see link 2007 DF250 Suzuki Marine Outboard FUEL PUMP - FUEL VAPOR SEPARATOR Diagram and Parts
see little filter number 27 if after changing all other filters the problem is still there that is where i would be looking and the most likely culprit .Comment
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