Re: 350 magnum mpi mysterious failures
are these engines closed cooling?<br />if both engines have detonated pistons and swallowed valves, by swallo I mean acutally pulled the vale into the head and "tuliped" the face, then its a classic sign of excessive combustion chamber temps.<br /> thre are a few causes, the biggest in the marine industry is overproped for the RPM your turning, boat that big and heavy I will try to prop it so it can turn 5200 or so.<br /> we have had issues in the past with the 5.7L motors swallowing valves. almost every one was over propped for the conditions.<br /> next time also check the fuel delivery vacum. a restriction can create lean issues that will burn pistons/valves.<br />and yes the ECU can mask many symptoms, wont hide them, a good tech with a laptop can see when things are actually an inrange failure or something is not right and the ECU doesnt "see" it. the ECU is mostly stupid, takes all sorts of inputs and makes a few outputs to modify its base map. occasionally if two sensors get to far off the ecu will set a code and power down.<br /> most older ones wont and the result is tulips for valves.<br /> without having been part of the assesment its hard to say but I would double check the propping, sometimes on those water campers with marginal power we have to underprop them to keep them alive. after that go through the check list about the causes and remidies for detonation and excessive combustion temps.<br />and on the next set verify ign timing and advance with a light not just the scan tool. I have seen some lieing ECU's.retarded ign timing can create excessive exhaust/combustion heat as can over advanced timing. usually the knock sensor will pick up over advanced, in fact if its knocking a lot the sensor will retard timing and can create the very problem its supposed to solve.
<br />Lugging due to incorrect props?....JK
