2007 DF225 RPM issue

[JDTOOM]

I’m hoping to get some help or suggestions with an issue I am having with my 2007 Suzuki 225. The engine won’t run over 2200 RPM. There is dead range on the throttle from about ½ to full. If I shut down the engine and reset the oil change reminder (kill switch X3) and then restart it runs up over 4,000 RPM no problem, runs great, and then backs itself off down to 2,000 or 2,200 and stays there. If I disconnect and re-connect the ECM wire it has the same effect as the oil change reminder. I’ve replaced all the filters and cleaned the VST. I tried hooking up a small skiff fuel tank directly to the engine with the same results. The engine and boat were only used for display at boat shows from until 2011. The engine had 40 hours on it in 2011 when it was put into service. It now had 230. The ECU cable was not initially hooked up and wasn’t connected until this season. Now that it’s connected she starts right up no problem but has this power issue. The Suzuki service tech replaced the neutral switch and the shift position switch. I did find bad fuel in the racor fuel filter which is why I replaced all the filters and cleaned out the VST. Is there any way to reset the ECU? Any other suggestions? Thanks

[JDTOOM]

Quick update: I can also get it to run up over 4,000 rpm initially if I turn the key to the first position and let it go through the start up sequence but do not actually start it. If I do this 3 or 4 times before starting it it will run over 4000 for the first few minutes and drop back down to 2200. After that it runs only at 2200 unless I either reset the oil reminder, go through the start up 3-4 times, or remove and reconnect the ECU. Now I'm thinking it's the LP fuel pump although with only 230 hours its not due to be replaced. Can I service the impeller or test the pump output or should I just replace it? I can hear it turn on and it sends gas into the clear filter but I'm thinking it's not keeping up with the demand at higher RPM. Thanks

[Harper2]

All these RPM figures that you're giving us .... this is with the boat in the water, with the gears engaged (prop turning)? And I assume that since you have put almost 200 hours service on it yourself that it was fine until recently? What do you mean by "dead range on the throttle from about ½ to full"? I also don't know what you mean that the ECU cable "wasn't connected until this season". What cable are you referring to here?

[JDTOOM]

Thanks for the reply. Yes, all the RPM numbers are in the water in gear/under load. Yes, the engine has run great up until this year. The ECU cable that I'm referring to is the memory wire that runs from the engine to the red terminal on the #1 battery. It was initially coiled up in the engine cowl which made the engine hard to start but it ran great. This is my first 4 stroke. The Suzuki mechanic did not catch it when they did the testing after the sea trial. Everything tested fine on the engine (like it was just delivered and still in the break in period according to the tech).
By dead range, I mean the throttle position from half to full does nothing. From neutral to about 1/2 there is incremental increase in RPM as the throttle position increases.

[Harper2]

Okay....now understand that I'm just an old shadetree type mechanic, so I didn't necessarily ask those questions in anticipation of being able to answer them all, but I thought it necessary to clarify so some others can help, too. In your analysis, I assume you shut down the engine to do such things as the oil remeinder reset and unplugging and replugging in of the ECU. On initial observation, because of these manipulations of wiring, this would seem to indicate something electrical, but I'm not so sure about that. You also mention letting the ECM go through its system checks before actually cranking. What I'm getting at is that merely shutting down the engine for a minute or two seems to temporarily help. So, as you a leaning toward, it could well be fuel delivery related. Have you tried just shutting down and doing nothing for a couple minutes, then starting back up again to see how the engine reacts?

On another note, I am not at all acquainted with any red "memory wire." On the mid-sized engines (inline four-bangers) there is a white sub-battery cable at the battery positive, but it is not a memory wire, since it is not connected directlly to the ECM, but to the coil power of the ECM relay. When the key is off, the white sub-battery cable is not providing any power to the ECM. Your 225 might be different and have some kind of memory power to the ECM, but I really don't think so. Most memory in engine ECMs is non-volatile and requires no constant power for memory maintenance. Have you only experienced your RPM problem since attaching that red wire, or was this happening before that?

So, I'm assuming that since you have not mentioned alarms, there are none. Hopefully some others on the forum will have some ideas where to look in trying to track down your gremlin, but I would first suspect the MAP sensor, and if not that, then continue to check out the fuel system (you might check the low pressure pump by applying power to it and running fuel into a container so you can measure the volume delivered in a given time before merely replacing it). And simply use a multi-meter to check some other sensors (temp sensors next). But if you're going to replace things on the motor, based on your symptoms, the first thing I would suspect is not the pump, but the MAP sensor (No, I don't know why the darned thing is so expensive). But I think you also need to check such things as the fuel pressure at the rail. You might have to hook it up to a computer to see if there are any fault codes.

[JDTOOM]

Thanks for the response. I guess I'm new to forums as well and should have included some more info. You are correct that I am not getting any alarms. And also correct that I didn't have any RPM issues until after the "memory wire" was connected. I'm also suspicious of the VST... When I mounted that unit back onto the engine I primed it but only up to the top of the small reservoir at the bottom. It occurred to me last night that I should have more gas in there and that maybe the HP fuel pump is out pacing the LP fuel pump at high RPM. How much gas should be in the VST? Can I prime it with out taking it apart again? I assume I can prime it by turning the key (half way) and pumping the primer bulb (and repeating the process a few times) or should I disconnect the gas tube at the VST top and pump fresh fuel in from there? Also, is it possible to have too much fuel in the VST? Sorry for all the questions but I'm not sure how I'll know exactly how much is getting into the VST without taking it apart again.

[Harper2]

Yeah, I'm leaning more and more toward a fuel problem, as you add to the info. I'm not exactly sure what the level of fuel should be in the VST, but the bowl in the VST has a float that controls the level of fuel (much like the float in a carburetor bowl), and that should be set to keep the fuel at the proper level. And you'll adjust the float height by bending the small tab on the float that sits on the needle. I don't know what the setting is for the float on your DF225, but for the DF150/175, the float height is 48±3mm. There's also a pressure regulator in the VST that could cause problems if it has failed.

[JDTOOM]

I'm not sure how to test the pressure regulator, but that might be my next thing to try. I borrowed a new ECU, hooked it up, same results. Primed the VST: same result. New fuel lines and tank: same. If I reset the oil change reminder it runs over 4000 RPM for a few minutes and then backs down to 2200 on its own and stays there. Shut down and restart: 2200. Only the oil rest will cause a short term increase in RPM's. All new filters and new gas. Any other ideas???

[Harper2]

Do me a favor (and yourself, too) and disconnect that red wire that you still refer to as a memory wire and trace it back to find out where it goes. You said yourself that the problem started when you connected that wire. The difficulty in starting that you experienced before you discovered the disconnected wire can be addressed after you know exactly what that wire does. See if disconnecting it solves your RPM problem.