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-   -   Help, Motor won't start. Merc 454 Mag EFI (https://www.offshoreonly.com/forums/general-q/311838-help-motor-wont-start-merc-454-mag-efi.html)

MILD THUNDER 05-04-2014 09:13 AM

There are two fuel pumps used on that engine. The mechanical, which fills the system, but is low pressure. Then there is the electric, which converts to high pressure for the EFI system. A fuel pressure gauge is really needed, to see if in fact you have enough system pressure. The little bit of fuel in the reservoir and 'little air" coming out of the valve doesn't necessarily mean the high pressure pump is working.

dmaxximus 05-04-2014 09:49 AM


Originally Posted by MILD THUNDER (Post 4116769)
There are two fuel pumps used on that engine. The mechanical, which fills the system, but is low pressure. Then there is the electric, which converts to high pressure for the EFI system. A fuel pressure gauge is really needed, to see if in fact you have enough system pressure. The little bit of fuel in the reservoir and 'little air" coming out of the valve doesn't necessarily mean the high pressure pump is working.

Ok, can you tell me where the elec fuel pump is located and if the is the fault of the system does that communicate with the warning horn when you turn the key? The fact that the warning tone doesn't come on when I turn the key again is telling me something isn't right to allow the motor to fire. Thanks again everyone, stranded on a nice weekend sucks for a boat that hasn't given me a prob in 3 years

MILD THUNDER 05-04-2014 10:16 AM

The warning buzzer simply turns on when you turn they, because the engine is not running, therefore, the sensors read something is wrong. Like, IF the engine was running, and you have zero oil pressure, the alarm would come on. Since the engine isn't running, there wont be any oil pressure, and the alarm sounds.

As I said, the alarm always has positive power when the key is on, and gets grounded thru the sensors. No oil pressure= switch closed=circuit completed=alarm comes on. The fact that the alarm isn't coming on when you turn the key, and is making a weird clicking noise, either simply means the alarm isn't getting power or ground, or the alarm itself is bad.

It would be very coincidental that the alarm failed at the same time as the no start condition occurred. I think when you find out why your alarm isn't coming on, is when you will find your no start cause.

The Electric pump should be enclosed in a black box on the engine somewhere, usually on the lower left side I think. I'm not totally familiar with that engine. If you are positive you have spark when cranking, that would pretty much rule out a bad ignition switch.

koolkats 05-04-2014 11:58 AM

I would swap ignition switch with the one that is working for a quick check as that could be the problem.

Bilgerat 05-04-2014 12:57 PM

Its not the ignition switch, if it cranks ( sending power down the yellow/red wire ) and if you have spark at the motor ( its sending power down the purple wire ) First thing I would look at is to be sure you have a good connection at the "Cannon Plug" the big connector for the main harness to the motor. THese sometimes get bumped cleaning, winterizing, etc. and are commonplace problems for supposed bad connections. THen if I follow everything else you have said, You have cranking, spark, and you think you have fuel ? It would run, but the question is back to that fuel situation.
Check the Cannon Plug.

dmaxximus 05-04-2014 01:45 PM


Originally Posted by Bilgerat (Post 4116848)
Its not the ignition switch, if it cranks ( sending power down the yellow/red wire ) and if you have spark at the motor ( its sending power down the purple wire ) First thing I would look at is to be sure you have a good connection at the "Cannon Plug" the big connector for the main harness to the motor. THese sometimes get bumped cleaning, winterizing, etc. and are commonplace problems for supposed bad connections. THen if I follow everything else you have said, You have cranking, spark, and you think you have fuel ? It would run, but the question is back to that fuel situation.
Check the Cannon Plug.

Ok will do and thanks but after cranking for a min I pulled plug right away and was really dry so no fuel to cylinders is my best guess. Can't find any fuses for fuel pump like someone suggested. I was charging battery's right before this happen so also wonder if I over charged and got a surge to pop breaker or fuse.

BUP 05-04-2014 01:57 PM

Closed sealed inline spark checkers to see if you have fire to the sparks plugs when cranking, next noid lights hooked to your fuel injector connections to see if they blinky blinky when cranking to see if you have power to the fuel injectors.
next fuel pressure readings when cranking,

all motors need - air - fuel - spark - correct amount of voltage and the forgotten one - compression to start and run.

Just for the sake of it put the motor in clear flood mode to try and start it. meaning put your throttle in start mode but at full throttle.

BUP 05-04-2014 02:00 PM

Seen your last post - if your electric fuel pump is not working at all it could be bad or the fuel pump relay is bad or a connection problem.

Also like I said you need to make sure you are getting power to your fuel injectors. When cranking engine over see if you are building oil pressure the reason like MT said the motor needs to see oil pressure then the electric fuel pump will pump as well. Not to go into great lengths of how all that works but that's the jist of it.

Pismo10 05-04-2014 02:02 PM

Spray a little bit of Gumout down the flame arrestor and crank. If it fires, it is a fuel problem, if not it is ignition. Always step one.

dmaxximus 05-04-2014 05:13 PM

Well thanks everyone but nothing has worked and I'm stumped. Couldn't find the elec fuel pump on either side unless it's the box mounted on top w the fuel lines running in and out. No fuses anywhere to check really and no breakers popped.
Guess it's time to take to a Merc Tec and BOAT for a simple fuse or wire fix. Ugghhhh


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