DF175 Problem

[wellcraft34]

Have a DF175 that has developed a problem. It starts right up and idles perfectly. Turns up, jumps boat on plane but will not exceed 4000 RPMS. Sounds good at 4000 but cant get anymore out of it. Have changed Fuel water seperator and low pressure fuel filter. Checked plugs too. Issue seemed to happen overnight, used last week and today has this problem.

[RussArran]

Could it be something to do with the throttle cable and/or linkage? Does the throttle lever keep moving forward while the engine revs level off, or does the throttle "stick" at 4k rpm?

[wellcraft34]

My throttle cable was in bad shape, so I thought that was it and replaced it. Same problem. Engine is throwing no codes. Throttle doesnt stick, moves smooth, I can throw the hammer all the way down and Im at 4000 RPM. I looked at the linkage and it appears to be opening all the way up. Its a 2007 model with around 900 hrs. Its kinda strange because the engine appears to be running great.

[wellcraft34]

UPDATE: Ran again today and same thing. I noticed when I was powering onto the trailer the RPMs started surging a bit. I pushed it a bit more and RPMs would surge from 4000 down to 2000 then it finally died and wouldn't restart. Got home and went under the cowling and noticed the fuel pump was no longer activating when I turned the key on. I guess it was the HP fuel pump all along?

[Harper]

Sure sounds like the high pressure pump, if it won't pressurize the system when your key is turned on. But I would remove it and check it all out really well, along with the whole VST to make sure there's no crud or contamination. And try to apply 12 volts to the pump directly once you have it out to see if it appears to be working. I wouldn't shell out money for a new one until I'd checked it all out thoroughly.

[wellcraft34]

I opened the VST last week to check the fuel pump filter, no contamination at all. Today I listened again, and the pump sounds like its trying to engage for maybe1 second. Definitely not the usual 6 seconds.

[wellcraft34]

Sure sounds like the high pressure pump, if it won't pressurize the system when your key is turned on. But I would remove it and check it all out really well, along with the whole VST to make sure there's no crud or contamination. And try to apply 12 volts to the pump directly once you have it out to see if it appears to be working. I wouldn't shell out money for a new one until I'd checked it all out thoroughly.

UPDATE: THought HP pump was no longer running so I opened up the VST to check and the VST was DRY. Turned key switch and HP pump is indeed pumping. Poured in some fuel to check, unhooked fuel line and it squirted fuel. Figured it was LP pump, being VST was dry. Fired engine up, ran good. Unhooked line feeding VST from LP pump and its pumping fuel. Im still thinking LP pump, is it possible for the LP pump to not operate at full capacity? LP filter is full of fuel so its not a restriction issue towards tank.

[Harper]

Did you check the needle and seat at the inlet to the VST? Make sure that the passage at the needle seat is clear. The float shuts the fuel flow off when the VST is full, then when the level drops, it lets fuel back into the VST. It works just like the needle and seat on a carburetor. I would suspect that, since the LP pump appears to be working.

[loweballz]

Were you able to diagnose this problem and fix it?
I ask because I have twin 2006 175hp Suzukis and I'm having the same problem on my port engine, as my max RPMs are 4200 while the starboard engine can meet the max RPMs as usual.
Thanks for any help.