502 Mag MPI Missing at 3/4 Throttle
 

I have a 1999 502 with about 200 hours and it intermittently misses/stumbles slightly starting at 3/4 throttle and above. I changed the fuel filter and it still does it. It's really frustrating since it only does it sometimes. Found a jumper wire that had some insulation missing and taped it up and it seemed to be fine after that. I had the boat out yesterday and the same miss came back. Anyone have any idea on what to check/replace? Spark plugs, dist. cap/rotor??? Any help would be appreciated.

Change all the stuff you listed.

Jumper wire for what???????

Thanks. I'll check it out this evening.

Agree with Griff that your best bet is to change the plugs, wires, cap and rotor. The rotor is a lousy design which combined with ECM based ignition advance steals most of the voltage from the coil just to jump the gap in the distributor. This happens when the ECM increases the advance beyond a certain point. All the ignition components need to be in perfect condition for it to work.

just a thought but I had a intermittent electrical issue that turned out to be a half broken piggyback connector at the dash. PQ has a wire that ran from the motor to a breaker on one of the dash switches. The boat would run great up to 4000 or so rpm, after that it would intermittenetly cut off, it was a pain in the ass to find, it took the connector to finally break for me to figure it out. when it broke I had no power to anything.

Same motor same issues, I think this may be my problem. Sometimes I have to push around wires underneath the dash just to get power to that motor :eek: