Engine running rough just off idle/ Power surge

[Thomas Chobot]

Having issues with my 1998 Merc 350 mag. The engine will run rough just off idle (at about 10-13 mph when surfing) When excellerating and the throttle about at 3/4 open it will seem to surge and increase in speed on it's own. After this happens, the engine sounds and performs better. Also I have a 3 blade prop on it and it does't seem to coming out of the hole like I would execept. Any ideas?

[boatwakes]

Is that the carb model? Is there a fuel smell in the exhaust when it's running rough? Smoke? Recent work done? Did you start with basic tune up (plugs, cap and rotor, ignition sensor if it hasn't been done yet)?

[Thomas Chobot]

Is that the carb model? Is there a fuel smell in the exhaust when it's running rough? Smoke? Recent work done? Did you start with basic tune up (plugs, cap and rotor, ignition sensor if it hasn't been done yet)?

It is fuel injected. Plugs were done 3 yrs ago, never replaced the cap, rotor or ignition senor since I owned it ** 200 hrs have been put on since I owned it. I do not put a lot of hrs.per year. No smoke or fuel smell.

[TeamAllen]

How old is the fuel? When was the last tune up performed?

[Thomas Chobot]

How old is the fuel? When was the last tune up performed?

Fuel is good Besides the plugs and the oil changes nothing has been done since i owned it. (250Hrs.)

[Thomas Chobot]

Is that the carb model? Is there a fuel smell in the exhaust when it's running rough? Smoke? Recent work done? Did you start with basic tune up (plugs, cap and rotor, ignition sensor if it hasn't been done yet)?

Where is the Ignition senor located? Also where can I get the replacement parts from, a auto parts store?

[Thomas Chobot]

Where is the Ignition senor located? Also where can I get the replacement parts from, a auto parts store?

Anyone???

[boatwakes]

Ignition sensor is located under the distributor rotor and sierra part number is 18-5116-1. Just google the part number and it will come up with different places to buy it. You can also go to perfprotech.com and look up your engine serial number for mercruiser part numbers and prices. Do not use auto parts on that engine, safety issues with ignition protected parts for everything except the throttle position sensor, which may also be part of the problem. Tune it up first and then see if that changes anything.

[Thomas Chobot]

Ignition sensor is located under the distributor rotor and sierra part number is 18-5116-1. Just google the part number and it will come up with different places to buy it. You can also go to perfprotech.com and look up your engine serial number for mercruiser part numbers and prices. Do not use auto parts on that engine, safety issues with ignition protected parts for everything except the throttle position sensor, which may also be part of the problem. Tune it up first and then see if that changes anything.

I have seen the throttle position sensor range in price $24-65
anyone know why there is such a swing in price?

[Thomas Chobot]

Ignition sensor is located under the distributor rotor and sierra part number is 18-5116-1. Just google the part number and it will come up with different places to buy it. You can also go to perfprotech.com and look up your engine serial number for mercruiser part numbers and prices. Do not use auto parts on that engine, safety issues with ignition protected parts for everything except the throttle position sensor, which may also be part of the problem. Tune it up first and then see if that changes anything.

When looked up the ignition senor on the perfprotech.com it doesn't show up on the drawing.They call it a module or am I missing something. The sierra 18-5116-1 will bolt right on? The ignition senor is orginial,does the sierra part look the same as the one I am replacing? Is this easy to install?

[Thomas Chobot]

Ignition sensor is located under the distributor rotor and sierra part number is 18-5116-1. Just google the part number and it will come up with different places to buy it. You can also go to perfprotech.com and look up your engine serial number for mercruiser part numbers and prices. Do not use auto parts on that engine, safety issues with ignition protected parts for everything except the throttle position sensor, which may also be part of the problem. Tune it up first and then see if that changes anything.

I ordered one of the sierra ignition sensor and it look nothing like the oem one that is on there none. What am i missing??

[Thomas Chobot]

I ordered one of the sierra ignition sensor and it look nothing like the oem one that is on there none. What am i missing??

Anyone????????????

[boatwakes]

That's why there was an updated part for it. The stock unit has exposed solder and wiring which would crack over time and cause a bunch of ignition issues. The new units are completely enclosed and waterproof with a ground wire incorporated as well. Connect the white with red and the white with green to their respective bullet connectors and then add the ground wire somewhere on the block.