Higher RPM misfire 1999 250 OX 66

[jf123]

Hope someone can help steer me in the right direction. I am experiencing a intermitten misfire at higher RPM's usually above 4000. I have done the following and all appears to be good. Replaced 10 micron filter, replaced water seperator, removed all injectors and cleaned filter screens, cleaned VST filter, checked TPS readings, checked O2 sensor readings. Fuel pressure test, Spark plug end caps were replaced as preventive maintenance during the spring. I did notice I have no issues at low speed and coming up on plane. I start to misfire once I am at cruise speed. I am leaning toward a faulty coil or coil pulser but not sure if testing will show anything bad if it happens intermitten. Any suggestions or ideas? One other question. When testing the TPS should the injectors all pulse at a certain postion in the TPS when I am testing output voltage?

[boats.net]

Intermittent problems are hard to find and usually have to troubleshoot while running at 4000 rpm's to find it.

[jf123]

One other question. When I test the TPS by checking the volatge sweep should I hear the injectors pulse at a certain throttle angle? Key on engine off linkage removed from cyl. one about halfway through my sweep they seem energize for a second. I don't recall this happening when I checked years ago when I had another issue. From your experience have you seen failure with the pulser coil or ingition coils. Is one more common to fail as apposed to the other or is this rare. Being intermitten I want to try and start with the most likely senario.

[boats.net]

Yes you may hear the clicking noise. Any electrical part can fail but is rare on Yamaha motors.

[jf123]

I was able to find my problem. The neutral safety switch located on the linkage is engaging while under way. Unplugged everything runs fine. So I have a few more questions. Is it possible to buy the whole assembly that it sits in or do I have to piece it together? The yamaha manual does show it as a switch assembly. Next question. I am currently running with it unplugged and from what I understand the switch is designed to interupt the ignition when shifting into gear. I notice no difference while shifting. Does this switch have any other function I should know about?

[jb123]

it only wont let you START in gear

[jf123]

I thought the switch in the shifter assembly was for preventing starting in gear. The one on the linkage does interupt the ignition when shifting into Fwd or Rev I suppose to provide a smooth gear transition. I do not see any adjustments that can be made to it. Does Yamaha sell the full assembly with the plastic pieces? I assume they are worn causing my problem.