Suzuki Df300 acceleration issue

[Unreel]

So I've been having a very specific issue with my 2015 300 last season. The engine will stop gaining rpm around 3800-4000 after getting on plane and the fuel economy drops significantly. You can tell the motor is more "under load" is the best way to describe it. I have to continue advancing the throttle forward and at a certain point the engine clears up and the rpms go up and fuel economy goes back to normal. It is very consistent at this rpm. After that the engine runs perfect up to wot. If i dont keep advancing the throttle and sit at that range it will continue running that way with the fuel economy way below what it should be, usually at that rpm I would be getting 8-9 gph, but it will shoot up to 13-14 until it clears up then drops back down. This is usually where i like to cruise at too as its the best fuel economy. Fyi I have the c10 gauge and fly by wire and im not getting any codes. I checked the fuel water separator and the onboard clear fuel filter and no water or debris. Next step to drain the vst and see what comes out. My thinking is either something inside the vst or something to do with the lean burn system. Dealer said he had heard of one or 2 other people with similar situation but couldnt remember what the issue was. Thoughts?

 

[chromatose007]

VST sounds like. Warranty?

 

[Unreel]

VST sounds like. Warranty?

Kind of what i was thinking. Going to drain it and see what comes out. After that ill probably take it into Breakers to deal with, last year of warranty.

 

[Sharphooks]

Yes, the VST —-if there’s gunk in there that wouldn’t necessarily throw a code, especially as it clears itself out at higher RPM as you mentioned

 

[Offshore]

Could be O2 sensor is dirty.

 

[Sharphooks]

Could be O2 sensor is dirty.

I think that would throw a code

 

[ship happens]

Yep, that would throw a code.

You know what would not throw a code? TPS voltage not moving past a certain point across the sensor.

Fuel pressure

Also is you loose a cylinder from either ignition or fuel related, it will feel like that.

 

[profisher]

I'm imagining that just like computerized engines in cars these new fuel injected 4 strokes all have an air mass sensor telling the computer how much air in entering the intake and mixing fuel accordingly. My van acted similarly and it was the sensor. and was a .quick and easy fix. Just throwing that out there as something easy to check if they do in fact have one as well.

 

[ship happens]

Your talking about the MAP sensor?

Intake manifold pressure sensor

I've never had to change one, however one time I had to carefully clean one. The ECU should pickup if that sensor is not reading the correct value and give a MAP fault.


stuck VST floats can also produce and over fueling issue and over flowing into the intake. That can trigger a MAP fault, but can also not. From dirtying up the MAP sensor. Typically you will have black smoke on engines like that one or a rough stumble if being over fueled.

The sensors on the engine are fairly easy to diagnose from the active monitor screen on diagnostics while the engine is running. It will show all the values. The manual will show what they all need to be in range of at whatever RPMs etc