Need Help!!502 Mpi Hole In Piston
 

WE PULLED JAMIE'S 502 MPI OUT. #6 PISTON HAD A HOLE ALL THE WAY THRU IT. HOLE WAS UNDER SPARK PLUG. PISTON IS HEAT DISTORTED ON TOP AS IF IT LEANED OUT. WE PULLED HEADS OFF OF OTHER MOTOR AND FOUND #6 IN SAME SHAPE. BUT NOT BURNED THRU YET. ALL OTHER 14 PISTONS LOOK PERFECT. MOTORS ARE STOCK EXCEPT FOR CMI EXHAUST, WATER CROSS OVERS,AND ARIZONA SPEED REPROGRAMMING BOXES.MOTORS HAVE APPROX 250 HOURS ON THEM. WHAT COULD MAKE THIS HAPPEN TO BOTH MOTORS SAME CYLINDER. WERE STUMPED WHAT DO YOU THINK OR KNOW? RON

Similar things have been know to happen on small blocks. One cylinder was always either burning through a piston or burning an exhaust valve. I believe Smoky Unick had that problem years ago and assumed it was either poor water flow around that one cylinder, or not enough fuel to that one cylinder causing a lean out... but if your engine is fuel injected... I would have a tendency to think that one cylinder runs hotter. According to the old hot rod guys... the way they circumvented the problem was by lowering the compression on just that one cylinder.... sounds crazy,,,, but that way they could run maximum ignition advance and fuel mixture on the other seven and get more performance than just rejetting and retarding.... Just my guess... good luck...

I have seen one clogged injector do that to an MPI engine. It is unlikely but possible you have the same problem on 2 engines. Or as Reed said there is a cooling problem-possibly due to the crossovers. Do you have any idea what water pressure the engines were running??

I KNOW HE DOES NOT HAVE PRESSURE GAGES

That is the problem cylinder on those engines. There are a variety of cures. Make sure that the bolts are not bottoming out, vent the heads, run a colder plug on #6 and/or a bigger injector.

Just for kicks, check the cam lobes for abnormal wear (degree wheel and dial indicator).

Could it be a programming issue? #6 getting too much advance or lean mixture?

It sounds very unusual to me that both #6 pistons would be running lean. Since both ECU's have been re-mapped, it sounds to me like another Arizona Speed and Marine screw up. How many hours have you put on the motors since having the ECU's done?

I would check the flow of those 2 injectors. Then I would check fuel pressure for both engines. If all that is OK then its the exhaust or reprogramming. Or a combination of both.

I've heard the same thing that the #6 cylinder typically runs lean in the 454/502 motors. I have no idea why.

I also don't think the ECU's are capable of sending a different amount of fuel to each injector. I think the computers are too dumb for that, especially if it is a MEFI1 system. It sounds like the motors in question are pre-serpentine belt applications, so they would be MEFI1. The MEFI3 ECU may not be capable of that either.