f115 missing/skipping at mid range RPMs

[SparkieBoat]

I have a 2003 F115 that cranks and idles perfectly and seems perfect at WOT, but it will shut off some when I put it in gear and go to start off, it gets better after the engine is warmed up, then I get a lot of skipping if i try to hold it below 3/4 throttle, after it warms up it gets better and only will skip intermittently at around 5000 Rpms.
It clears up at WOT. my thoughts are along the lines of the throttle position sensor...I have new plugs, and yes they are the right ones according to the little sticker on the motor. any ideas gentlemen??

 

[jeffersondodson561]

Re: f115 missing/skipping at mid range RPMs

If you are going to check TPS you will need to do so with an analog meter, you can't see the natural wiper sweep with a digital one. Also check for proper fuel pressure and fuel pressure regulator operation.

 

[SparkieBoat]

Re: f115 missing/skipping at mid range RPMs

Thanks..i will have to get the tools for those test.

 

[SparkieBoat]

Re: f115 missing/skipping at mid range RPMs

I have done some checking and am now very suspect of the filter that is at the bottom of the high pressure pump, It is called the VST chamber... I have heard also that there is a check valve that can fail and allow fuel to run backwards leaving air in the lines and causing low pressure pump failure..it is called a relief valve. any ideas on how to test the relief valve? it is an expensive little bugger. I read somewhere to get a small section of clear fuel hose going into the motor and look for backflow. does this sound right??

 

[99yam40]

Re: f115 missing/skipping at mid range RPMs

test fuel pressures while problem is occurring or have them tested if you do not have the tools. that will tell you if there is a restriction. If it is running lean it will harm the motor by running it that way

 

[SparkieBoat]

Re: f115 missing/skipping at mid range RPMs

where is a good place to get the tool to test fuel pressure on this motor?? and what should the pressure be? I have all tools to work on carbed motors, this is my first fuel injected..so might as well get what I need..Thanks Sparkie

 

[jeffersondodson561]

Re: f115 missing/skipping at mid range RPMs

Any automotive store should have what you need. Or if you have a Harbor Freight, I have seen a fuel pressure kit there that looks decent.

 

[99yam40]

Re: f115 missing/skipping at mid range RPMs

I would recommend picking up a Yamaha service manual for your motor. It will tell you the specs, the equipment needed, and the steps to test all systems on the motor

 

[SparkieBoat]

Re: f115 missing/skipping at mid range RPMs

manual and fuel pressure gauge kit on the way..