Help!!! boat falls on its face @ 3000rpm

jdub · 08-12-2006, 09:28 PM

27 excalibur with a 1994 502 efi. The motor runs fine then around 2800 to 3000 rpm it breaks up. If I stab the throttle it will rev high but backfires. The only way I can get the boat on plane is to drop the tabs and drive. Once I start to trim up and the rpm's increase the motor breaks up and the boat falls on its face. I checked and changed the fuel filters and nothing. Seems like its starving for fuel at the higher rpm's. Anybody got a fix?

teka228 · 08-12-2006, 09:33 PM

Yeah but it sure looks pretty doin' it!!!

Even though your having a problem.......it was still a good day.

dean51267 · 08-12-2006, 11:35 PM

check your coil, long shot but cheep to test....

JJONES · 08-13-2006, 02:04 AM

Bad plug wires will cause cyclinders to drop under load!

Outdrive1 · 08-13-2006, 02:59 AM

Check your fuel pressure, how many hours does your motor have and how many hours and years on your electric pump? If you've never changed it you've been lucky to get that many years out of it. if your motor looses fuel pressure your knock sensor will engage and cut your ignition momentarilly. That will usually give you sense of it breaking up, similar to an electrical short.

mats · 08-13-2006, 03:15 AM

As have been said, check your fuel pressure when it breaks up. Likely causes; fuel filters, antisiphone valve, fuel pump

jdub · 08-13-2006, 07:42 AM

I will check pump and pressure this morning.

Payton · 08-13-2006, 08:07 AM

Is the a secondary filter that you are missing? I know Merc had a screen after the main filter on the 496s that was giving some people problems.

jdub · 08-13-2006, 09:23 PM

Thanks for the thoughts guys but it was a bad ECM. Swapped one and it ran fine. I was able to run it pretty hard until I found another problem, water in the oil.