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.