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Can someone who knows the 2001, SX250 (ox66) explain the working and testing of the fuel system on this engine. Low pressure pumps, high pressure pump, filters, injectors, where does it mix with oil, testing pumps using pressure gauge .?? Thanks
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the three lift pumps(low pressure) mov fuel from the hull tank to the vapor seperator.
the high pressure pump,on OX66, is located inside this tank.
the electric pump always has 12V on the red lead when the key is on.
the pump ground path is con*****ed by the ECU.
it routes the ground through a resistor,about .55 Ohms, at RPM's below about 1200.
above 1200 the ECU selects a striaght ground path.
this gives a 2 speed pump operation keping the fuel cooler and the pump current draw down.
high pressure can be tested at the scharder valve on the VST.
the engine oil pump feeds all 6 outputs to a manifold then through a check valve and into the VST where its mixed.
the ECU fires the injectors based on pulser coil inputs.
#1 pulser triggers spark on #1 and injection on #2.
each injector has a replacable filter installed in it.
I use the mercruiser filters for a late 90's 7.4 MPI engine.
the SX250 also incorperates CCS.
this is Controled Combustion System.
this fires all 6 below about 800 RPM,drops #5 from 800 to about 1200 RPM, from 1200 to about 1800 RPM it drops 2 and 5.
if any sensor is out or unpluged base ign timing becomes fixed at 7* BTDC and engine le speed increases.
this applies to all sensors EXCEPT the O2 sensor.
if the O2 sensor is unplugged fuel is fixed rich at low speed and lean above 4000 RPM.
incredibly simple speed density EFI setup that has been around over 20 years. -
rodbolt, thank you
Thank you for taking the time to go through this explanation. I now understand it much better, as this old motor is new to me. I ran these motors (twins) for the first time last season, and they ran great. So I am just looking to understand them a little better. YOU should write a service manual !!! I see you put in a lot of time here on this forum and for me it is greatly appreciated. I read your posts with great interest. Thank you for that , I realize it is valuable knowledge, and skills that you CHOOSE to share. Best Regards, and thank you againComment
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one more question about lift pumps
Do these pumps lift fuel from one to the other ? or do they independently each pump fuel to the vst? thanks againComment
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each pumps to the VST.
that motor can blow through 25 gallons/hr at WOT.
the lift pumps,VST and injector filters MUST have maint or a piston goes poof.Comment
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