Yamaha 1999 250HP ox76 idle problem

[moonlightin]

Having idle problems and top end power problems. boat just won't idle consistently. no power over 3500 RPMs

here is what i have had done.

1. Compression test
2. replaced oil float level switch
3. replaced 3 new fuel lift pumps
4. replaced VST fuel filter
5. checked high pressure fuel pump 38psi
6. checked fuel pressure relief on vst
7. ran engine on shop tank with good fuel supply
8. swapped out ECM
9. scaned engine for touble codes NONE
10. performed injector resistance test
11. checked pulser coils
12. checked engine timing
13. swapped out high pressure fuel pump
14. checked 02 sensor
15. cleaned all engine grounds and checked all connectors
16. tried running engine with shift/ throttle cables disconnected
17. checked main engine relay
18. changed boat batteries
19. syncronized throttle bodies
20. adjusted TPS voltage sensor
21. checked for vacuum leak on fuel line
22. CAN GET ENGINE TO IDLE WITH YELLOW LEADS DISCONNECTED AT ECM UNIT
(no wire diagram for computer)
ENGINE SNEEZES AND SPITS WHEN LEADS ARE CONNECTED
NO VOLTAGE LOSS AT FUEL PUMP WITH LEADS DISCONNECTED
ENGINE WILL ALSO RUN WITH KNOCK SENSOR DISCONNECTED
23. checked all ignition coils
24. checked for spark on all cylinders
25. install new spark plugs
26. check stator output
27. checked for propeller slippage
BAYTESTED BOAT WITH HIGH END POWER LOSS (EXTREME)

HELP!!!

 

[rodbolt]

Re: Yamaha 1999 250HP ox76 idle problem

have you tried sending the injectors out for cleaning?
when you dissconected the yellow wire at the ECM you forced it into fixed rich at low speed and fixed timing.
unplug the knock sensor and timing will be fixed at 7*BTDC and idle will increase to about 1100 RPM.

 

[moonlightin]

Re: Yamaha 1999 250HP ox76 idle problem

no i haven't. would that cause both the stalling and the loss of power at the high end?

 

[PBJohn]

Re: Yamaha 1999 250HP ox76 idle problem

Check the shift switch for proper operation. Probably won't cause a stall but will give you a misfire. What do the spark plugs look like after running? Fouled? clean?

 

[rodbolt]

Re: Yamaha 1999 250HP ox76 idle problem

remember on that engine NO codes are STORED.
they are only displayed when its active.
you may be fighting two issues.
use the diagnostic test lamp but at the engines normal load and the trouble RPM.
a loose knock sensor will mess with a mind.