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454 Mag MPI fuel problem

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454 Mag MPI fuel problem

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Old 08-02-2005, 08:14 PM
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Default Re: 454 Mag MPI fuel problem

Had my motor checked on the merc scan tool and no codes came up, none where stored in the memory. Talked to the mechanic who ran the test and he recommended replacing the IAC motor, a couple of the other techs recommended the same as well. I bought a new one for $80 buck and installed it, the boat fired up on the hose fine and started with authority numerous times. The marina bid not even charge me for the test, I guess that is a fringe benefit for being a former employee. I guess time will tell if this is the permanent fix, but the engine sounded alot healthier at idle and start up.
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Old 08-02-2005, 10:52 PM
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Default Re: 454 Mag MPI fuel problem

I had similar problem and it ended up being the fuel pressure regulator. I did replace the IAC and got it from automotive supply house for a lot less than the "marine" version. Exact same GM part numbers.

My pressure regulator and rusted and was binding the diagphram. THe rust ( and the GM part number) were covered by the pain the manufacturer had applied. It had almost rusted thru when it started causing problems and we tested everything and changed the IAC before we discovered the rust bubles in paint.
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Old 08-03-2005, 06:32 AM
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Default Re: 454 Mag MPI fuel problem

Thats an even better price!!
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Old 08-07-2005, 09:08 AM
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Default Re: 454 Mag MPI fuel problem

Well it did it again. Althougth this time it did not even want to idle and suck air, it just plain wouldn't fire over. I let the boat sit for an hour and it fired up just fine. I am begining to think that it is vapor lock. Where is the fuel rail shrader valve??

What is the VST? Where is it on the motor? The motor is a 1999.
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Old 08-07-2005, 09:33 AM
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Talking Re: 454 Mag MPI fuel problem

well, sorry to hear that you still have the problem. The shrader valve should be in the front of the intake area just under the center of the plenum. Right around the t-stat housing. If your motor has a VST tank, this will be located on the odd bank side at the rear. (port) It will have 2 hose going to it and 2 wires. It will be on top just next to the distributer.

Good luck, keep us informed.

John
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Old 08-07-2005, 09:44 AM
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Default Re: 454 Mag MPI fuel problem

The vst is a vapor separator tank it acts kind of like a fuel bowl in a carburetor in the chamber is a fuel pump, float, needle valve the idea is to bleed out any air in the fuel line so the motor doesn't vapor lock and has a contsant suppy of fuel.
Attached Thumbnails 454 Mag MPI fuel problem-vst-pic.jpg  

Last edited by GOODT; 08-07-2005 at 01:18 PM.
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Old 08-07-2005, 11:15 AM
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Default Re: 454 Mag MPI fuel problem

Thanks for all the info guys!!! I post what I find.
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Old 08-07-2005, 11:22 AM
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Default Re: 454 Mag MPI fuel problem

There is some good information about vapor lock in Mercruiser Service Bulletin 99-7. A pdf file of this bulletin is available at another site. Not sure if its ok to post link here.

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Old 08-07-2005, 11:42 AM
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Default Re: 454 Mag MPI fuel problem

go ahead and do it , its ok if its for the help of a fellow boater
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Old 08-07-2005, 12:00 PM
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Default Re: 454 Mag MPI fuel problem

Mercruiser Service Bulletin 99-07

http://www.boatfix.com/merc/Bullet/99/99_07.pdf

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