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Old 05-17-2015, 08:45 PM   #1
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Default Mercruiser won't start

Hi everybody. Before i take the boat to the shop and spend more $$$ I'd like some advice on what could be the problem. The Mercruiser 5.0 won't start. It almost does but not completely. So far a mechanic shop replace the fuel pump stating that the pressure was too low. The boat started and work 1 day. I am back with the same problem. I have a new alternator and fully charged both batteries. Both batteries were charged at home. They were load tested and are in good condition. The day the boat worked, i noticed that if I run it at low rpm for about 5 minutes or more it starts to run rough until i accelerate and "clean it". Any ideas on what else i should check? Thank you. Andre
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Old 05-17-2015, 10:06 PM   #2
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Welcome aboard

A few questions

When did it last run good?
Anything happen to it since then?
What year?
Carb of fuel injection?

So it cranks fine, correct?
When not running have you checked that it is getting fuel, spark?
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Old 05-18-2015, 12:50 AM   #3
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Thank you so much for the quick reply.

When did it last run good? Before i had half a foot of water in the boat (forgot to remove the plug and we got rain.
Anything happen to it since then? The water under the engine may have reached the starter
What year? 2000
Carb of fuel injection? Carb ( think) I'll check tomorrow.

So it cranks fine, correct? not really. it starts slow like the battery is too weak despite the fact that the battery is full charge.
When not running have you checked that it is getting fuel, spark? not yet. doing that tomorrow. good idea thank you.

Here is my theory so far. the starter is going bad and drawing more current than normal. That makes the voltage drop below 10 volts. i read that if it drops below 10 it won't start. What do you think? Thank you again for your help. Andre
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Old 05-18-2015, 03:14 AM   #4
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If you know the starter is weak - and had been submerged- I would change that and eliminate (or discover ) that is the issue. You need a new starter anyway it sounds like. So it won't be wasted money.

That is the next step I would take. FWIW...

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Old 05-18-2015, 03:19 AM   #5
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So starter may have had water in contact with it.

Corrosion will cause a voltage drop which translates into low voltage at the starter and slow cranking.

Being a 2000 the fuel pump is electric and when cranking gets powered by the starter solenoid. If the solenoid was under water it may have corrosion on its contacts and the fuel pump may not be getting proper voltage.

Seems it's all centered on the starter. I would start there.
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Old 05-18-2015, 03:30 AM   #6
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How high did the water go? Have you checked your oil?
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Old 05-18-2015, 01:41 PM   #7
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I think you are on the right track with the starter. When is the last time the engine had a service done to it?
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Old 05-18-2015, 03:12 PM   #8
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Thank you guys for the corrosion explanation on the starter, Makes sense. Before i pull the plug i saw the water just under the engine. The last maintenance was last year so i'll replace the starter and do an oil change.

Does anyone know if the engine needs to be lifted to replace the starter? They had to lift it a bit to replace the fuel pump. I'll go try today.

Thank you again for all your help. I'll report back after i replace the starter. Andre
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Old 05-18-2015, 03:24 PM   #9
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I was able to replace my starter without moving the engine, but that depends on engine room configuration and stringer interfere, not the engine. After you pull all the wires, its just 2 vertical bolts.



Use anti-seize on the bolts when you reassemble.
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Old 05-18-2015, 03:34 PM   #10
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Quote:
Originally Posted by andre757 View Post
Thank you guys for the corrosion explanation on the starter, Makes sense. Before i pull the plug i saw the water just under the engine. The last maintenance was last year so i'll replace the starter and do an oil change.

Does anyone know if the engine needs to be lifted to replace the starter? They had to lift it a bit to replace the fuel pump. I'll go try today.

Thank you again for all your help. I'll report back after i replace the starter. Andre

Depends on engine compartment layout, you did not state what model boat you have. You may need to remove the starboard exhaust manifold to gain access.

I find it hard to believe they had to life the engine to get access to the fuel pump. Hopefully they checked the engine alignment afterwards. If the alignment is out it will cause the coupler to wear.
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