My 2000 454 mag mpi is acting up!
Runs great for 20-30 mins, then backs off and revs 2400 rpm or so. Sounds like it is running on 6 or less cylinders, and loses power.
Back off throttle and idles fine. Will plane and get up to speed when throttle applied again. Cuts out quickly.
Replaced the fuel filter/water separator, gas didn't appear to have any water in it.

Any ideas where to check next would be helpful, I'm running out of boating season!
ryan

What kind of fuel presure do you have? Either electrical or starving for fuel

Pull a plug and see how they look, plug wires also

i had this problem in my old mariah, my coil was bad.

IAC or TPS......beg, borrow or steal a scan tool, saves the headache.......

SORRY to hijack, but, last year I had a similiar problem, the boat would fire right up, but, would "surge" at idle, ran great, and wouldn't stall or anything, but, the "surge" at idle was annoying, I bought a new IAC, but, haven't changed it yet, is there anyway other than a scan tool to tell if the TPS is bad? I would like to change both [if need be] over the winter, Thanks, and SORRY!

Michael

TPS - use a VOM test voltage output and resolution

Any updates on this, I'm having this problem with my port engine. Power is good for 20-25 min then I start losing power. Come off plane idle's fine get on plane a minute later start losing rpm's and power. Oil pressure/Temp all good.....

just for kicks...is you transom turning black at all

mines not if you were asking me......