Pr. of 2000 Merc. 502 MPI's (MEFI 3). Rebuilt the stock 415 hp using the 500 hp package recommended by Mark Boos at Precision Marine: .578 lift cam, 2.25 intake valves, 3-angle exhaust valve job, K&N air intake, Gil exhaust, MEFI remapping etc. etc. I also had the stock injectors bench cleaned and tested, 1 was replaced. I'm blown away by the increase in power (9 mph on the top end) and torque. But, here's the gremlins in (I think) the injection system: First both engines show an intermittent miss in the tach. Sometimes after start up 1 or both tachs will bounce a little at idle. A speed run will often make it go away. Other times they're steady at start-up but will show a miss after a run. Next, the port engine has twice only made around 5700 RPM's at WOT instead of the +/-5100 both have been making. After the first time it happened on the way home, it again made 5100 the next time I took it out. Then the last time it again topped at 5700. I put my scan tool on it today and the error code it showed before I started it was #34: Manifold Pressure Sensor Low Voltage, and General Warning #2: Telltale Indicator. I assume that's related to the #34 code, but I haven't had a chance to research it in the Merc manual. After I cleared the code and started up, it didn't set any more errors. Everything was within spec including Manifold Pressure: 14.9 at start-up, 16.9 after warmed up and Manifold Pressure volts: 2.15. I didn't have time to take it for a run. Any ideas or suggestions are appreciated!