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Help, Motor won't start. Merc 454 Mag EFI

Old 05-05-2014, 08:27 PM
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You obviously have no power to your fuel pump so work backwards. Is there power going to the fuses? To the relay? At the main harness? Going off memory when you turn the key switch it puts power to the fuses and then lights up the relay which in turn powers the fuel pump.

Also, as stated make sure it isn't the ignition switch. I know you have spark but I'm not 100% sure the route the coils get spark from. When you turn the key to the "on" position that should power up you fuel pump. The fact that it isn't and there's no alarm would make me check the switch. It may be possible to have spark and starter without the fuel pump. I had the wire from the first post fall off, and my fuel pump lost power, but it would crank as that is jumping to another post on the switch. No clue if I had spark as I never checked. The fact that I had no fuel pump made me look at the switch first and I got lucky. I also had a relay go vutvit shouldn't affect the alarm. I might be wrong bit It takes 2 minutes to check the switch.

Last edited by onesickpantera; 05-05-2014 at 08:43 PM.
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Old 05-05-2014, 09:04 PM
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Originally Posted by onesickpantera
You obviously have no power to your fuel pump so work backwards. Is there power going to the fuses? To the relay? At the main harness? Going off memory when you turn the key switch it puts power to the fuses and then lights up the relay which in turn powers the fuel pump.

Also, as stated make sure it isn't the ignition switch. I know you have spark but I'm not 100% sure the route the coils get spark from. When you turn the key to the "on" position that should power up you fuel pump. The fact that it isn't and there's no alarm would make me check the switch. It may be possible to have spark and starter without the fuel pump. I had the wire from the first post fall off, and my fuel pump lost power, but it would crank as that is jumping to another post on the switch. No clue if I had spark as I never checked. The fact that I had no fuel pump made me look at the switch first and I got lucky. I also had a relay go vutvit shouldn't affect the alarm. I might be wrong bit It takes 2 minutes to check the switch.
Thanks, that's where I initially started was looking at the starter switch and safety switch. I swapped the safety switch cause it was easy with the working side but did the same so somewhat eliminated that. Didn't try swapping the stater switch cause figured the odds of that going bad was pretty high.
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Old 05-05-2014, 09:20 PM
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Originally Posted by dmaxximus
Thanks, that's where I initially started was looking at the starter switch and safety switch. I swapped the safety switch cause it was easy with the working side but did the same so somewhat eliminated that. Didn't try swapping the stater switch cause figured the odds of that going bad was pretty high.
You dont have to swap them. There are three posts on the back of the switch. One has 12 volts all the time, one will have 12 volts when you turn the key to on and the third will have 12 volts when turned to start. Check the first post with a test light when the key is turned to on(and make sure the wire is connected).

Last edited by onesickpantera; 05-05-2014 at 09:23 PM.
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Old 05-05-2014, 10:20 PM
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OK BACK TO THE BOX....If you test for power their at all 3 fuse leads on both sides,,all those leads are triggered from the ecm...the landyard safety tether that goes to your wrise also goes to the ecm which powers up the ecm..check the circuit brakers and what ever side of the tether feeds power to the tether or lantyard to power up the fuel side of the ecm that provides power to the fuel pump..like i said some boats have more then one fuse panel..

if it all checks out either your ignition module is bad or your ecm took a crap..
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Old 05-05-2014, 10:33 PM
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he said it will fire if he gives it a shot of starting fluid so i think his problem is lack of fuel.i think his best bet is to get and follow mercury,s flow chart.
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Old 05-05-2014, 10:44 PM
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New electric fuel pump along with the new fuel filters and whatever cool fuel set up this 454 has either VST or cool fuel II possible problem in that area.

Another simple test is try a portable fuel tank like for outboards instead of the boat fuel tank and fuel line - put a primer bulb inline with your test fuel tank & fuel line, pump the primer bulb until it wont pump anymore - then try starting your engine - reasons are you need to make sure its the motor side your having fuel delivery problem.. IMO you need what I posted above.
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Old 05-06-2014, 06:57 AM
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He has spark and he has momentum. He is lacking fuel. He has removed the pump and tested it with 12 volts and it worked.

He stated the fuel pump is NOT kicking on and his alarm quit sounding when the key is turned to the on position. That is pretty coincidental IMO, so I would start at the switch and work from there looking for power. I may be wrong thinking the switch can affect the fuel pump without affecting spark as I don't know exactly how the system works, but since it is a easy test that is where I would start.

Like Mild Thunder said, a test light and wiring schematic will go a long way here.

Last edited by onesickpantera; 05-06-2014 at 07:14 AM.
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Old 05-06-2014, 07:25 AM
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You should be able to "hot wire" the pump tho. the 2 wires coming out of the VST are for the pump. Get some test leads and hook it up to 12v and see if it works and start tracing the 2 wires back from there. They cant be to long since the computer is right next to it.

On a side note: Last year I had same thing happen with no start. Now ever in the end I just had to tap on each injector with a screw driver. The pintle in each injector was stuck closed from sitting all winter from the cleaner.

Last edited by 92nsx; 05-06-2014 at 07:27 AM.
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Old 05-06-2014, 12:09 PM
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Check the wires from the fuses where they start into the lid of the ecm/fusebox. I had a short there where it rubbed thru the black tape and insulation. Mine was the ignition fuse though.
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Old 05-07-2014, 09:31 AM
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Originally Posted by onesickpantera
You dont have to swap them. There are three posts on the back of the switch. One has 12 volts all the time, one will have 12 volts when you turn the key to on and the third will have 12 volts when turned to start. Check the first post with a test light when the key is turned to on(and make sure the wire is connected).
Ok thanks again to everyone, I will just replace the fuses in the VST box even though they all appear good, I can't find any other fuse boxes in the boat to check then try the volt test on ignition switch. Something is not allowing the fuel pump to turn on. Again I double tested the pump and it spun up fine, I even ran power to it (not a great idea) while cranking and no start. Communication issue for certain
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