2005/115/4-Stroke Won't Speed Up

[captaincrab55]

Good Morning, My 115 Yamaha won't push my boat above 7 MPH, but did go 40plus. It was a sudden change, no in between issues of moderate speed issues. I changed the plugs, but they looked great. I replaced the OB fuel filter and the water separator filter too. I'm thinking injectors or throttle position sensor as the culprit. Would it pay to purchase diagnostice software for my YAMAHA and would that point me in the right direction?

Thanks,

[rodbolt17]

all the sensors can be tested with a standard digital multimeter.
fuel rail pressure is critical and can be monitored with a simple gauge avalible at most parts stores.

if the TPS failed you would also complain about a high idle speed.

[captaincrab55]

all the sensors can be tested with a standard digital multimeter.
fuel rail pressure is critical and can be monitored with a simple gauge avalible at most parts stores.

if the TPS failed you would also complain about a high idle speed.

rodbolt, Thanks

[captaincrab55]

Cylinders 1 and 3 aren't firing. Compression is 150 for cylinders 1 & 2 and 145 for cylinders 3 & 4. Both dead cylinders share different coils. Now where?

[captaincrab55]

CaptSolo, I flush the engine with ear muffs! I let the rain rinse my motor, I'm not using it in very salty water.

[captaincrab55]

Capt Crab... You mean you never take a hose to the outside of the engine with fresh water?

You take the cowling off when it rains only?

I let the Rain Wash the Cowling! I only remove the Cowling for Service and Checking the Oil!

[captaincrab55]

Looks like a code 28 Shift Position, but it doesn't say if it's a switch or sensor. I ran out of daylight today and hope to resolve the problem tomorrow.

[captaincrab55]

CaptCrab:

Code 28 shift position sensor - I get this all the time when I start the engine in gear. Just erase with the YDS and move on.

I'm not a mechanic, but from what you wrote, I think your problem is in the "coils" not doing their job and the two dead cylinders. Do you have the YDS?

CaptSolo, Thanks! I hope to get back on trouble shooting today. I had a chance to read around during the rain yesterday and your advice is dead on. Now I need to delete code 28 and see if I can retrieve another code. Now I need a DVA meter or adapter for one of the multiple meters. Just seems strange that 2 coils go at the same time. Half of each coil is acting up, just wondering if a sensor is acting up? The motor is starting to run rough at low idle too.