Engine Misfire!

[Gsewell]

Hi All ,

My boat is a 1996 Maxum 1800 sr with 3.0 Mercrusier. Noticed when putting the engine under more load. Crusing speed then full throttle the misfire happens. I have just replaced spark plugs and leads and makes no differnece. Coil? Distribruator ?

Anyone had similiar problems with this engine misfire?
Thanks
Gordon.

 

[dubs283]

Did you inspect/replace any other tune up parts? Cap/rotor, fuel filters, check/set timing/idle?

First guess is fuel starvation at higher rpm/load. Inspect the fuel delivery system from tank to carb, fuel pump pressure/vacuum

 

[Gsewell]

Did you inspect/replace any other tune up parts? Cap/rotor, fuel filters, check/set timing/idle?

First guess is fuel starvation at higher rpm/load. Inspect the fuel delivery system from tank to carb, fuel pump pressure/vacuum

Hi , No just replaced plugs and leads.
The misfire goes away once you get above the rpm where it occures. Fresh fuel has been put in. I don't know the full history of the boat maintenance . Just bought it. Maybe carb/ fuel pump needs inspected like you say?

 

[Scott06]

Hi , No just replaced plugs and leads.
The misfire goes away once you get above the rpm where it occures. Fresh fuel has been put in. I don't know the full history of the boat maintenance . Just bought it. Maybe carb/ fuel pump needs inspected like you say?

Ok if you just bought it some basic maintenance is likely needed

what do spark plugs look like ?

agree likely fuel related, would inspect and change fuel filter, clean and rebuild carb, inspect cap and rotor.

has water pump impeller engine oil gear lube been changed? Inspect bellows for cracks

 

[Gsewell]

Ok if you just bought it some basic maintenance is likely needed

what do spark plugs look like ?

agree likely fuel related, would inspect and change fuel filter, clean and rebuild carb, inspect cap and rotor.

has water pump impeller engine oil gear lube been changed? Inspect bellows for cracks

Sparks looked like they have been in for a while and 1 plug was a bit bent damaged. That's why i thought replace plugs and leads and se how it goes first.
Does this engine have a in line filter?
Coil and cap looks like its orignal.
Engine oil and filter looks recent.
Will check exhaust bellows for cracks.
Thanks.

 

[Scott06]

Sparks looked like they have been in for a while and 1 plug was a bit bent damaged. That's why i thought replace plugs and leads and se how it goes first.
Does this engine have a in line filter?
Coil and cap looks like its orignal.
Engine oil and filter looks recent.
Will check exhaust bellows for cracks.
Thanks.

Normally a 3.o will have one filter in fuel pump bowl and another in carb inlet. Both are small. You can follow the fuel line back to tank and see if someone added a canister fuel filter to it. If its only happening at WOT probably best to measure fuel pressure at WOT. Could be a plugged fuel tank vent

Don't forget to look at drive lube should be greenish blue not black and have no milkyness.

If cap and rotor look original look inside for corrosion and arching wear on contact surfaces

Check driveshaft bellows and shift bellows for cracks. While exhaust bellows can crack and split they are full of water anyways. Driveshaft bellows and shift bellows will let water in the boat ruin gimbal bearing, u joints, and potentially drive input shaft seal.

 

[Gsewell]

Normally a 3.o will have one filter in fuel pump bowl and another in carb inlet. Both are small. You can follow the fuel line back to tank and see if someone added a canister fuel filter to it. If its only happening at WOT probably best to measure fuel pressure at WOT. Could be a plugged fuel tank vent

Don't forget to look at drive lube should be greenish blue not black and have no milkyness.

If cap and rotor look original look inside for corrosion and arching wear on contact surfaces

Check driveshaft bellows and shift bellows for cracks. While exhaust bellows can crack and split they are full of water anyways. Driveshaft bellows and shift bellows will let water in the boat ruin gimbal bearing, u joints, and potentially drive input shaft seal.

Thanks for all the info and things to check. Should keep me busy for a while. Hopefully get to the bottom of it.