300XS Hesitation 1900-2400rpm

[redbird555]

HI all so I've got an 09 300xs. Motor runs great at idle and part throttle but stumbles in the 1900-2400 rpm range. If I accelerate it will hit that window and bog until i apply more throttle and then it'll snap out of it and rocket up to 5400 wot and never miss a beat, its solely in that window.

I have done the basic services, new fuel filter, new fuel line going to the motor, replaced the vst filter and new plugs. I have not looked at the actual vst to see if it has dirt inside or the diaphrams inside the pulse pump. Basiaclly looking to see if anyone has an idea on what could be the issue? Low pressure pump, dirty vst or the pulse pump?


Thanks for the help!

[Euroski]

how many hours and has the fuel and air injectors been cleaned? Also WOT should be 6000rpm so maybe need prop change?

[redbird555]

how many hours and has the fuel and air injectors been cleaned? Also WOT should be 6000rpm so maybe need prop change?

motor has 460 hours on it. I’ve only owned it for about 60 hours so I’m not sure if they ever have been. Prop may be a tad big but this is on an offshore CC with a fleet master lower so wot is specs at 54-5800

[Euroski]

motor has 460 hours on it. I’ve only owned it for about 60 hours so I’m not sure if they ever have been. Prop may be a tad big but this is on an offshore CC with a fleet master lower so wot is specs at 54-5800

is this something that just recently started? Did it ever run well with current prop?

[redbird555]

is this something that just recently started? Did it ever run well with current prop?

Well i have tried a few different rpms thinking it might be that but they all seem to do the same thing. Last prop i ran had me up around 5700 but the midrange was terrible. As far as I can remember i believe it was doing the same thing.

the prop does have vent holes on the bottom that are fully plugged. maybe i should try tkaing them out and see what happens?

[redbird555]

also i might note that the motor is running poorly, like if i leave it at say 2200 you can feel it shaking and ht watch the rpms surge. i sort of feel like it was the prop it would still run smooth and ust not be able to "push" the boat so to speak

[XstreamVking]

A scan would be a good idea. I would go with a coil connection problem or a fuel rail diaphram spring sticking. Could be an injector too.

[redbird555]

A scan would be a good idea. I would go with a coil connection problem or a fuel rail diaphram spring sticking. Could be an injector too.

i had it out just for a bit today and tried a couple things. Not sure if they will help though.

i revved up to about 1900-2100 which is where it starts running rough. I then slowly applied throttle and noticed that the rpms did not move at all. In other words I was opening the throttle but saw no change in rpm. Then all of a sudden I reached a certain point and the rpms shot up to 3k and she took off. Started cruising at 4200 no issue and even opened it up to 5600 no problem with a light chop.

then when I slowed down I backed off the throttle slowly and stopped around 2800. Then without moving the throttle the motor gradually started to buck and running rough and the rpms dropped down to about 2k where they stabilized.

does this sound like a possible TPS issue? I just can’t seem to shake the thought that if it was a fuel issue I wouldn’t be able to cruise at 4200 much less wind her out at 5600 no issue

[Euroski]

My suggestion: stop guessing, stop throwing parts at it without first doing a scan. Want to save $$$ then take to knowledgeable mercury dealer shop.

[redbird555]

My suggestion: stop guessing, stop throwing parts at it without first doing a scan. Want to save $$$ then take to knowledgeable mercury dealer shop.

I have thrown $0 in part at it. The plugs and fuel filter are part of seasonal maintenance that I do anyway. I also haven’t had time to get it scanned....it’s been 4 days and during the week lol. Thanks for the helpful tip though

[kellytheaker]

The Question on - did it run fine With that prop before - ? Didn' get answered .... So go back to props and start there - AND many times I heard Scan it - great idea ! Do it . But basics - try another lesser pitch . Make sure your propped correctly - minimum .

[InjectorService]

So many things to check. Intermittents will be tough to find. Do you want to diag it yourself? I personally start with air & fuel pressure on every Opti. It is quick and not worth looking into anything else if those are out of spec.

[TraceF3]

You can buy the testers for about $12 on Amazon. Buy a pair so you can do air and fuel at the same time. Looks like a fancy tire gauge and stays at the max pressure it senses.