2001 yamaha 250hp problem.

[bernieb]

I have posted on this engine several months ago and here is where i'm at now.With a 115 hours on the motor and the Model turz ox66 efi and the engine as of now starts instantly ,smokes a little at start-up but the smoke is gone after a minute,and last time out on a try-out the rpm's was surging up and down several hundred at a time on the upper rpm's,if I kept the rpm at 1100 or below no surging of rpm.I have replaced three new low pressure fuel pumps and the fuel pressure is 37psi at the shrader valve and in using a hand vacuum pump it drops 2 pounds pressure but goes to 37 on the release of the pump that is on top of pressure regulator.at idle the throttle position sensor is .48v ,full throttle is 3.6v .air temp sensor and air pressure sensors are within spec.The crankshaft sensor is way out of spec, I'm getting 5.5 v cranking ,should be .5v and at 1100 rpm i'm getting 24v .The book says the testing voltages .5v at cranking is minimum,so its got me confused. And rodbolt don't beat your head against the wall ,i did clean oxygen sensor and putting my finger on number one air hole went to .9v and on the release danced between .4v and .7v. Compression is 135 to 140 on all cylinders.I always had a low idle problem after a warm up ......400rpm to 700 rpm. sorry for long post. bernie

 

[rodbolt]

Re: 2001 yamaha 250hp problem.

sounds like its moving along, what is the fuel rail pressure when its surging?<br /> it must not vary more than about 2 psi at WOT.<br /> you crank position sensor voltage seems way high, have you tested the resistance and clearence?<br />have you tested the plug caps?<br />is the vapor seperator filter clean? is the pressure regulator filter clean?<br />what is fuel system vacum at the lower lift pump intake at WOT?<br /> a quick run with the diagnostic test light attached will reveal any codes for computer monitored failures, if all the above check out it may be time to pop the injectors out for cleaning/testing.<br /> remember that with the test light in place it wont automatically transfer oil.<br />but all alarms will function.

 

[bernieb]

Re: 2001 yamaha 250hp problem.

This tuesday i'll take it for a try out with the fuel pressure guage in place.on the crank position sensor the clearence is .010 and thats tight, and i'll check for the pressure regulator filter,didn't know it had one.i have replaced all six of plug caps as two were bad and i now got 4 for spares.From what i see the crankshaft sensor is only a coil and am i right in thinking that as the teeth from the flywheel causes a buildup and a collapse of a magnetic field the cdi uses this as a timing sequence ? what should i look for in ohm's to the sensor,to the computer? the vst filter is clean but didn't know about the filter on the injectors,but will clean. (what is fuel system vacuum at the lower lift pump intake at wot?)you ask .If i put a vacuum guage on a "t" fitting preceeding the lower low pressure fuel pump will that do what you ask? ......thanks bernie

 

[rodbolt]

Re: 2001 yamaha 250hp problem.

yep the CPS is a coil that the ECU uses for an aid in ign timing, the ECT is used to supply the ECU info on engie operating temps, the IAT supplies info on the intake air temp the aps supplie info on intake air pressure(barometric) for another air density input, the O2 sensor supplies the ECU with the amount of oxygen in the exh stream. between all the varios sensors the ECU determines the correct amount of injector on time to insure a clean burn at about 14.7/1. the only thing is the ECU has to assume the correct fuel flow. the flow is based on the injector physical opening and the 35PSI behind it. the ECU has a map that will turn the injector on for varying periods of time. it cannot measure rail pressure nor actual fuel flow(dirty filters), it has to assume that mechanically the fuel system is ok.<br />the resistance of the CPS is 179-242 Ohms.<br /> output loaded is 4v at 3500 rpm with a dva meter.<br /> the knock sensor will retard ign timing if knocking is detected. thats why the diagnostic test lamp is so handy, it will quickly tell me what is not broken.<br /> 99% of my EFI issues are O2 sensor or fuel related.<br />its rare to actually have a broken part, usually its filters and such.<br /> fuel system vacum at the lift pump intake should be 1.5-6"Hg any less usually indicates air leaks and anymore indicates a fuel restriction.<br /> if rail pressure varies more than about 2 PSI at WOT the system wont work cause the ECU is to stupid to see it. if you see the needle bouncing on the rail pressure it indicates a lack of fuel to the regulator or a regulator malfunction.<br /> you can use a pair of needle nose on the rail return to play with pressure, insure you dont allow rail pressure to exceed 60 PSI , if at say 40 PSI the engine runs better suspect clogged injectors.<br /> and all this is fun to play with on the bracket at 45 MPH .<br /> you can also try spraying premix down the throttle bodies.

 

[bernieb]

Re: 2001 yamaha 250hp problem.

^bump.<br />Got the boat out again on the water and with fuel pressure gauge attached stayed at 37 psi at all rpm's and the vacuum gauge in the fuel line preceeding the under the hood filter stayed at 2inhg and under load was about 4in hg. With a plastic auxillary gas tank with a can of seafoam in it and at one run, it run great at 43oo rpm's but other times before it was the up and down rpm's again .I checked the crankshaft sensor again but under load this time and the 1500rpm was 4.5v and the 3500 rpm value was 5.5v ,which was close to what Clymer's yamaha manual called for. I made the mistake of using a wrench on the shrader valve hook-up to the pressure gauge and broke off the thin brass threads ,but it held for the tests. The motor runs great ,but it's the varying rpm thats got me. I have to put it in storage for now and have fogged the motor, but will get the winky-blinky and will clean the injectors this fall......thanks to all. bernie