I have a 502 MPI MAG with a M-3 sc ProCharger running 5-6 lbs boost, ECU and headwork done by Precision Marine. I have an extreme loss of power on takeoff with a popping (backfire?) noise on the port side. I am down 800 rpm, from 5200 rpm at wot to 4400 rpm! I have replaced the dist. cap, rotor button, plugs and wires and get the same. The oil looks fine.. no milk. What should I look for next? I have not checked timing or compression yet.

anyone?

Your next step is to pull the valve covers and look for valvetrain problems,especially on the offending side. If you find nothing a leakdown test might show something but i bet you'll find something in the valvetrain if youv'e already checked the ignition. I had problems early in the season with comp cams rocker nuts cracking and backing off,everyone tells me i must be overtightening them BUT,never had that problem before on MANY motors i have built and the new arp rocker nuts haven't given me any grief. When the nut cracked and backed off the pushrod bent then rocker fell off valve,motor sounded seriously hurt,was POPPING and making metallic noises from intake valve letting mixture in ,firing with no way out,Smitty

Pull plug wires and make sure you didn't drop a cylinder. Check fuel pressure and make sure there is no fuel restrictions. The popping sounds like a fuel problem.

I installed a fuel pressure gauge in the dash when the ProCharger was added, fuel pressure is fine. I am leaning towards a blown Felpro head gasket between the cylinders, to lose 800 rpm that would have to be at least two cylinders down, do you guys agree with that?

i would be willing to bet on a bent or tuliped valve or bent push rod

I agree,my motor also has a m-3 procharger and like i mentioned earlier a valve train problem 1 month ago gave me exact same symptoms,Smitty

pop followed by big loss of power= something broke. like smitty said you most likely have valve train problems. At worst it's probably a sucked valve, is your fuel old or poor quality ? this is the most common cuase of tulliped valves in a marine engine especially a force fead engine. You can either start by pulling the valve covers or doing a compression test, I'd start with the compression test so you can be sure of which side needs to come apart but I'm sure youll find the problem in the valvetrain.

No procharger here but I had a loss of rpm recently (~800rpm too). Pulled it apart and found a couple of bent pushrods and the valvetrain wasn't lashed correctly.

Tim

I too have the same problem,( no procharger) and not sure what it is. Did you notice noise in the valve train from the bent push rods?
Did the motor constantly pop through the carb.? I only sometimes here a pop through the carb. Any help is greatly appreciated.
Thanks!