502 mag mpi popping sound
 

Hi everyone, I have a 502 mag mpi with 480 hrs and rebuilt last year by previous owner and he had bbc camshaft and 308 dart heads installed. Boat runs awesome when cold then gets up to operating oil temp around 180 ish and starts making popping sounds then lose power and idles rough, leave it for a minute runs fine again then starts acting up when back up to 180 ish. Compression is 127 in all cylinders. Fuel pressure is 39 at idle. Any help would be appreciated

Who and how was it tuned??? It should have had the ECM tuned and should be running at least an adjustable fuel pressure regulator??

theres alot to be checked on that engine,compression seems low,popping is an exhaust valve hanging up,why,could be a couple of things,guides tight,timing retarded heating up the guides,spring pressure is wrong,lash not right(tightened to much) tune to lean..........

I agree, too many things that it could be. If it were mine, I would look for the obvious and if I didn't find anything substantial I would just pull it out and do the troubleshooting and repairs on a dyno. This is one of those issues that may take all season or longer to figure out an hour at a time every other weekend.

Lets go cheap first. There probably is a fuse in the use Block connected to the key on switch in the boat somewhere. What type of boat is it. If you dont have a fuse block diagram just pull 1 fuse at a time at the dock while idling until it cuts off. If it has any corrosion on it replace it and spray a little DeoxIT corrosion inhibitor on it. Next replace rotor and cap. Next replace coil and and wire that goes from cap to rotor. Not saying this will fix it but it will eliminate some things and probably cost under 200.00. If you can get access to a scanner have it scanned.


Chris

It’s a 99’ fountain fever 27. I’m looking for the best possible way to go at this correctly whether it’s electrical, mechanical, fuel, or ignition.

The things I mentioned are all Cheap and you can do yourself. They are also considered General / Preventative Maintenance So if you have to take it to someone when you give up you can give them a list of what you did. Saves money.

Chris