2005 - 5.7L Mercruiser 350 MAG MPI WILL NOT START

[stelios hondrcolos]

If put some gas directly down the in take, it will start and idle smoothly. This leads me to believe it is not the ECM or 90 amp breaker

Are you sure the transmissions are in neutral?

Ask me how I know to ask this question.

If it was not in neutral it would not crank. which it does
.

 

[Todd320]

Cut the harness off, install quick connects, use auto store fuel pump relay, 14v40amp. You will at least know it’s not the harness. Bought my boat in 2016, first trip, relay died. Second trip, harness failed. Third trip, relay again, fourth trip, cut it all off. Then relay died on Starboard engine, cut harness off there as well, no issues since. Same exact symptoms. It could be your fuel pump(s) have failed. That’s next if this easy fix does not work.

 

[skolbe]

Cut the harness off, install quick connects, use auto store fuel pump relay, 14v40amp. You will at least know it’s not the harness. Bought my boat in 2016, first trip, relay died. Second trip, harness failed. Third trip, relay again, fourth trip, cut it all off. Then relay died on Starboard engine, cut harness off there as well, no issues since. Same exact symptoms. It could be your fuel pump(s) have failed. That’s next if this easy fix does not work.

Yes the fuel pump relay, I have witnessed a dock neighbor with the issue. It just melts. I would start there as mentioned.

 

[scoflaw]

If put some gas directly down the in take, it will start and idle smoothly. This leads me to believe it is not the ECM or 90 amp breaker

If it was not in neutral it would not crank. which it does
.

Not true, the ecm commands the injectors. Run your voltage problem down with a test light.

 

[stelios hondrcolos]

Does anyone know the GM auto part number for the fuel pump relay?
attached photo is a relay which looks burnt but i swapped it with other engine and it worked. Anyway I want to replace relays. Mercury and Sierra parts nos. are
807057T 18-5851 but i heard GM relays at NAPA are same thing and half price

 

[hughespat57]

Be sure to use ignition protected relays not cheap automotive ones

 

[stelios hondrcolos]

Made progress, but not their yet. I jumped the pump relay (Pink- Green and Pink - Yellow) and the pump would run. I then replaced the relay and closed it up It started and ran normally the rest of the day. But after a long period of sitting, the same thing will happen again. I need to jump the relay connections, and then close up and start as normal. Then it ran all day ( 30=miles) perfectly. So I think I have a strange intermittent control or wiring problem. What to do next?

 

[Highliner]

Did you replace the relay base? As in the connectors the relay plugs into?

 

[kvduff]

Did you replace the relay base? As in the connectors the relay plugs into?

This may help
https://www.amazon.com/Dorman-645-568-Fuel-Relay-Connector/dp/B00IWMX0XW

 

[stelios hondrcolos]

Did you replace the relay base? As in the connectors the relay plugs into?

I think this is my next thing to do. Funny enough the last two days it has started normally. I am thinking not to touch anything until it acts up again.

 

[stelios hondrcolos]

This may help
https://www.amazon.com/Dorman-645-568-Fuel-Relay-Connector/dp/B00IWMX0XW

I would like to replace it with an OEM Mercruiser connecter part if there is one made. I cant find a part number for one. It would be nice to keep the pigtail wire colors consistent for the next time someone has to get into it. Ive seen replacement available from Hella as well. Would like to find the best one.

 

[kvduff]

I would like to replace it with an OEM Mercruiser connecter part if there is one made. I cant find a part number for one. It would be nice to keep the pigtail wire colors consistent for the next time someone has to get into it. Ive seen replacement available from Hella as well. Would like to find the best one.

Not sure Mercruiser makes a connector but the link I sent you has substantially heavier gauge wire. I just helped a friend install one a few weeks back. I wouldnt worry about the colors if I wanted to use my boat.

 

[stelios hondrcolos]

Not sure Mercruiser makes a connector but the link I sent you has substantially heavier gauge wire. I just helped a friend install one a few weeks back. I wouldnt worry about the colors if I wanted to use my boat.

Thanks everything is working at the moment. I'm sure it will shake loose again and I will replace it. I have some time to order the correct part just making sure. If an OEM with colored wires is available i would use that.

So I guess this is simply cutting the connector out, and butt splicing a new one in with heat shrink tubing. Simple as long as the wires go back in to the correct terminals.

 

[stelios hondrcolos]

Just to update - I ended up splicing in a new $25 harness connector and she has been running fine for weeks. Thanks for everyone's suggestions. Probably saved me $500 repair bill if I could even find an available mechanic

 

[Pirate Lady]

That $500. Its a boat, you’ll drop it next week on something else.

 

[stelios hondrcolos]

That $500. Its a boat, you’ll drop it next week on something else.

Yeah, but I;ll drop it on hookers and blow. Not the boat. I do 99 pct of my own work on two boats and it saves many thousands per year

 

[Fill Ess]

You might need to get that as your boat name:

 

[Bt Doctur]

GM Blazer fuel pump relay, ign protested and rated at 30 amp. protects the flimsy oil pressure switch contacts