06 HPDI 250 / Hard starting & poor idle

[Papa Basscat]

there are times when the motor will catch and start with the first turn of the key. Most of the time it wont start on the first turn of the key and then I have to give it some throttle and keep the starter engaged for a couple of seconds to get it to start and then the idle is really poor. I put it in gear and it runs perfect throughout the RPM range. A few months ago I used the info from this site to replace all filters; replaced both low pressure fuel pumps; replaced the "mystery" filter and pulled the injectors and had them serviced. That was all done for a different reason than the idling issue but I have had a problem with starting and idling before that. Compression is good; new ball installed; etc. Butterflies are clean and look good. VST looked clean when I was in it replacing the VST Filter. I know the fuel is good and have new plugs in it, etc. The last time anyone touched the linage etc was in Mar of 2010. I noticed the idling issue started in the winter of 2012. It hasn't gotten worse but it hasn't gotten better either.

CAn anyone explain the theory of operation and our what is going on from the time the key is turned on and engine starts? There are only two Yamaha mechanics within 75 miles of me. One almost cost me a power head and the other one is backed up for 5 weeks. Any help or ideas are welcomed.

THanks for the help!

[rodbolt17]

when the key is turned on the ECU "wakes up".
it then turns on the medium pressure pump.
when the ECU sees a crank signal it defaults to start mode and timing is fixed,injection is fixed and it starts.

[Papa Basscat]

Good info and thanks; The ECU needs what other input for a normal start: IE Input from temps sensors; TPI; etc?

[Papa Basscat]

Also: Does the ECU keep the injectors open longer and or shorter depending on block temp or air temp? My problem is pretty much the same in winter at 25 degrees or summer at 90 degrees. Of course it is a little harder in winter. Thanks again: and HAPPY Fourth of JULY!

[rodbolt17]

the ECU gets a cranking signal from the start solenoid.
it then defaults to a start map.
once running it will then look at temp,TPS and crank position.

[Papa Basscat]

Last two questions "I Hope" ha-ha. How sensitive / dependent is the start sequence in relation to cranking RPM; and should I be able to hear the mid range elec fuel pump run for a second or two when i turn the key on; The pump is 7 rears old and has about 800 hours of run time on it. Would a worn pump be a possibility? I would think a pump is either good or bad. The last diagnostics that was done had fuel pressure OK.

I would think that once the engine starts the sensor inputs and ECU output adjustment signals happen within a second or two if not less. Which means I need to pay very close attention and focus on what is really happening when I turn that key on and start it. Awesome stuff. I love a challenge and this technical stuff. I was a M1A1 Tank Master Gunner in the USMC. Miss this kind of stuff.

Thanks again for your help. You are a wealth of knowledge and experience!!!!!

[rodbolt17]

nope, this stuff sucks.
I was an FC2,CIWS tech, on a destroyer.
yes the medium pressure pump will run and develop 50 PSI for about three seconds at key on.
should maintain 50 PSI at all RPM ranges.
High pressure pump should maintain about 1000 PSI at all ranges.
HP sensor output voltage should stay about 3.2V at all ranges.
will bump about a bit but not much.
voltage is read orange to pink at the sensor.