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HELP!!!!!!!! 1999 H2x 454 EFI motor bogs/shuts down at high rpm's

cx hatch

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Hi, I am new to the site. I am having a problem with my 99 H2x, after the motor was rebuilt by a pretty rep. marine shop I am having a few problems, Im just wondering if anyone knows where i should start.

1999 H2x with 454 (385 HP)

1. The motor sounds a little rough at times after warming up, normally about 30 min of run time, like it's not running on all cylinders etc.

2. At wide open throttle the motor will basically shut down/ bog down (I believe around 4200rpm) Losing all power. The motor does not die but basically shuts down.

Im just wondering where to start? My guess is a fuel or ignition problem? Just wondering if someone on this forum has had the same or similar problem I am having. Any help on where to start would be greatly appreciated! Thanks again guys!
 
Ayuh,... I'd start with checking the Fuel Pressure, Right when it starts bogging out...

How are the fuel Filters,..??
Fuel Tank,..??
Fuel Lines,..??
 
Try running on a separate fuel source....jerry can, to eliminate external fuel supply issue. If it still dies, do the "Wiggle" test. Run the engine and start wiggling all the wires, harness etc and see if you can get the engine to stumble. Check the main battery cable to the starter and make sure it's a good tight connection.

Does the engine horn still work/hooked up after re & re (beep on start-up)?
 
Make sure the plug wires are routed in paralell, not crossing each other. See if they are tight to the plugs. Bondo is steering you in the right direction. Fuel delivery pressure is important. Does the volt meter gauge needle jump around when it starts to shut down? Poor ground connections?
 
Thank you very much for the replies. I was out of town working without intenet access for a few days. I will try what you guys said and get back with you. As for the engine horn, it was disconnected quite a while back, stupid I know but the boat was running great at the time and the horn went off every 10 seconds. As for the volt meter, it does not jump around but hey you never know with these things, boats are a wiring nightmare!

Thanks once again for the replies, Im sure I will get the problems worked out, you guys all seem very knowledgeable. If you have any more suggestions throw them at me, I will try them all.
 
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