problem with volvo 7.4 caughing or missing when rpms over 2100

[eeure]

I have a Volvo 1998 7.4 gi with a Dps outdrive. To start I was just on lake Powell launched last sat and ran fine until wed afternoon after getting fuel. The motor will start fine idle fine and engage a run at low idle and up to about 2100 rpms fine if I go over 2100 it will cough and you can hear that the cyclinder did not fire it will loose momentum and then continue on as if nothing happened for another 30 to 40 sec and do it again. If i try to run at wot it will cough all the time and I did not try but once for fear of damaging the motor
Yes my first thoughts were bad fuel or water in the fuel. I checked the fuel filter and checked the fuel in it to see if their was any water and found it was clean. Checked the rotor and plugs all looked ok. I did not sound like it was the same cylinder each time but don't know because we were on the water in the middle of the lake. Got home now and thought I would see if anyone can start me off in the correct direction.
Thanks

[moxboating]

check the batteries make sure they are not taking all the charge from alternator. Sounds similar to my 7.4 problem i had one battery was dead, and i could idle around find but when i gave it full throddle it would cut out like it had a fuel issue. Happend to find out on the lake the alternator was extremly hot. was able to shut the dead battery off and worked great till i got a new one. check it out and see if it works anyway.

[bruceb58]

What model do you have? Need the full model number. Some engines have the SLOW system which disables the spark over 2100RPM if the engine temp or oil pressure swich shows as a fault. These are sepearte senders form what your gauges are hooked up to so they may look totally normal.

[moxboating]

It is a93 Mariah 2350z with a 7.4 Volvo penta the boat runs great now

[bruceb58]

It is a93 Mariah 2350z with a 7.4 Volvo penta the boat runs great now

Was asking the OP.