496 HO popping at 4000 rpms
 

We have a 36 Outlaw with twin 496 HO's. When we get to about 4000 rpms, I hear a popping sound coming from one of the motors. The rpms didn't drop a noticable amount, just he popping sound. I couldn't tell which one was actually making the noise while driving the boat. The motors have about 140 hrs on them and run great otherwise. Any thoughts on what is causing this issue?

My dad had a similar problem on his 496, only under load though. We couldn't repeat it on the trailer. Ended up being a cracked spark plug.

I had the same problem this year when I put the boat in for the first run of the year, when you pushed the throttles and she was under a load it would pop and lose power. Turned out to be corroded rotor & distributor cap.

mine started yesterday ! i can be at 4500 rpm with throttles half way.. and no sound.. the minute i push further , the popping starts. if i let go the throttle a little, it is perfect... only under load at 4500 + ... any ideas ?

No rotor or cap on a 496HO.

Start with the basics. Have the motors scanned to check for codes. If nothing shows up, move on to the fuel supply. Make sure all the filters (water/fuel separating + the automotive-type metal canister in-line one if equipped) are good and not plugged. Check your fuel pressure while running on both motors. You could have a booster pump down on one motor. You should be able to hear them energize when you turn the key on. If that all checks out, it could be something with the ECU not advancing the timing properly for some reason or a bad plug or plug wire.

This will turn out to be a bad plug or plug wire.. If plugs are over a couple years old then try that first..

Chris

I had the same issue with a 305mpi in my old Crowline. I replaced all the sparkplugs and wires and never had another problem.

My boat is at the shop for the same thing.