If it doesn't have the drain plug not sure why it would fall off after being winterized?

Item 11 it blue plug and the black box is decoration, has no functional purpose
https://www.mercruiserparts.com/bam/...1912/4854/100\

I wouldn’t even worry about it! I run mine without the cover and no issues whatsoever!

If we can reattach it we will, if not I'll run it with out it. Plan on pulling motors next year so it might have to wait till then for it to be put back on.
Thank for the help on this it was driving me nuts.

As stated, imo the cover is just a decoration. I ran my 2000 MPI's for 20 years w/o the covers till I upgraded the pumps when I did a full rebuild.

Finally ran the boat a few days ago and boat ran good for the first 40 minutes then starboard motor started stuttering and didn't want to go over 2500 rpm's, slowed down to idle to check everything'
all gauges were fine motor idled ok nothing visibly wrong. Got back on plane and all was good for about 10 minutes the it started acting up again' keep boat at 2500 rpm's and it ran fine, I don't think
this has anything to do with the cover so I'll have to start checking I guess for fuel or electronic issue?

Getting hot your fuel pump may act and give less pressure
had that problem years ago.

Weak fuel pump or restriction in fuel line Fuel line collapsing, antisiphone valve, fuel filter
Put a fuel pressure gauge on the rail and watch

Definitely will check fuel pressure and also going to do tune up on both motors hopefully this week if work doesn't get in the way , and see what happens.

Exactly what my 99 500EFI's would do until I quit running fuel with ethanol and kept the blower on when the engines were running. That was three years ago when I bought the boat. Been running rec fuel since then without any issues.