Put about 5 hours on newly rebuilt 2000 gen VI 7.4l MPI and decided to run it wide open ........ Well, after about 90seconds at full throttle, 4300RPM, 50mph, 24P props, slowed back to normal cruise at 30mph and heard that rythmic rapping sound. Oil pressure 40psi, water temp 175, everything normal and engine running perfectly...............

I suspect some kind of detonation pounded a rod bearing. possibly a lean condition? Engine starts and runs perfectly but has the knock during a no load condition. Idling you can't tell anything wrong. Engine will be pulled next week and hope to get by with a rod bearing change.

Machine work done by experienced shop but there was some changes made and I wonder if this resulted in a lean condition? Stock engine 310HP

Changes: New small chamber Vortec iron heads that were ported and large 2.19/1.81 valves installed. 454 magnum hyd roller cam used .510/.540 lift with dual springs. K+N filter and newly cleaned/flowed fuel injectors.

Motor ran perfect and had tremendous torque at 3,000rpm. would these changes be enough to cause a lean condition? Of course I need to find the problem but I will read the plugs and check the fuel filter/ water seperator for contamination. Any ideas or anybody ever had a similar problem?? TIA TBF

Did you have the ECM recalibrated for the mods?????

Before you get too carried away cut open the oil filter to make sure its a bearing.

+2

+2 !?!??!?!?!?!

With the amount of work you did......you should have reprogrammed the ECM.......unlike automobiles, these have no adaptive learning/compensation for mods.

Did you replace the oil cooler or have it professionally flushed????

Thanks fellas... I have not checked the oil filter but will tomorrow. I did check the dipstick and saw no reflective particles and oil looked perfectly new. If this is not a flattened bearing what else could it be? It certainly does not sound valvetrain related at all......... Can somebody recommened a place to reflash my ecm?? Thanks.... TBF

Mark Boos at Precision Marine. Look him up and give him a call. He is awesome to work with.

Odds are you went lean and burnt a piston. You may have damaged your rod berrings. You will not know for sure untill you get it back apart. Did you upgrade your oiling system?

If you are really lucky maybe its a loose flywheel. coupler or even ujoint in the drive..... Just a little optimism for you. Cut the oil filter open and let us know what you find.