Mercruiser won't start

[andre757]

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

[mmwjr]

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?

[andre757]

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

[Sled600]

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...

Rocky

[mmwjr]

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.

[Kevlar7r]

How high did the water go? Have you checked your oil?

[itsabowtime2]

I think you are on the right track with the starter. When is the last time the engine had a service done to it?

[andre757]

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

[Kevlar7r]

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.

[mmwjr]

Originally Posted by andre757

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.

[andre757]

Hi everybody, ok. i attempted to get the starter out. i remove 2 screws and pull out the motor. After looking online at what a new one look like i can see that i only took the motor out and not the casing. The casing is bolted with bolts on the opposite side. i can barely touch one bolt band the other side is not reachable. The solenoid is mounted on the casing. The solenoid seemed to be working fine. The motor has a gear that goes inside a gear box. all teeth look good. The solenoid is on top of the started and probably did not get wet. I am thinking buying a starter and replacing the motor only. Is usually the voltage drop cause by corrosion in the motor? Any thoughts? Thank you. Andre

[andre757]

Sorry i forgot to say the model. 2100 SR 2000

[mmwjr]

Originally Posted by andre757

Hi everybody, ok. i attempted to get the starter out. i remove 2 screws and pull out the motor. After looking online at what a new one look like i can see that i only took the motor out and not the casing. The casing is bolted with bolts on the opposite side. i can barely touch one bolt band the other side is not reachable. The solenoid is mounted on the casing. The solenoid seemed to be working fine. The motor has a gear that goes inside a gear box. all teeth look good. The solenoid is on top of the started and probably did not get wet. I am thinking buying a starter and replacing the motor only. Is usually the voltage drop cause by corrosion in the motor? Any thoughts? Thank you. Andre

I would replace the entire starter. Taking a new one apart to just use the motor will void any warrantee.

I still think the solenoid is part of the problem as well as the connections to it.

[andre757]

ok makes sense. Thank you Mike. I ordered the whole starter and i'll have it install next week. I'll report back. Thank you all for your help.

[andre757]

I am back. I replaced the starter. i used a fully charged battery and the same thing happen. Cranks slowly then stop. This time the negative post of the battery stared melting the rubber cover. i now suspect a short somewhere. Any suggestions on how to troubleshoot this? i do have a volt/ohm meter and know how to use it but i need some guidance on where to start. Thank you so much. Andre

[Sled600]

Check all the big connections for tight and corrosion. With a new battery and a new starter, spinning over shouldn't be a problem. I think you have a bad connection soneplace. Try the other end of the negative cable first. That is my 2 cents...,

[mmwjr]

Are the battery cable and starter cable connection corrosion free?

Slave solenoid connection corrosion free?

Check slave solenoid for voltage drop across the two large terminals when cranking, should have zero drop. (Volt meters red and black lead on either terminal).

If all this checks out. Pull all of the spark plugs and examine them.

With the plugs out see if the engine cranks better.

Use a strap wrench on the balancer and see if the engine turn easily by hand.

[andre757]

Thank you guys. I'll check that tomorrow.

[itsabowtime2]

Curious, have you checked your oil? Is it clean? Milky?

[andre757]

Milky. As soon as i get the motor to run i'll change the oil. Thank you for bringing it up