2004 Mercruiser 3.0 Won’t start, misfires & runs rough when starts.

[Omann68]

2004 Mercruiser 3.0 Alpha One I changed my spark plugs, distributor cap, changed oil, changed lower unit gear oil & replaced the alternator & power steering belts. It started but ran rough at around 3000-4500 rpm, now it won’t start and blows black smoke out of the carb when trying to start. I made sure the rotor is in the correct position and ensured the correct firing order. I’m not sure where to look next. Can anyone please help me?

 

[Fun Times]

Hi there, welcome to iboats.

What spark plugs and plug part numbers did you put in new? Are they the same length as the old plugs?

Distributor cap cracked maybe ?

Do you smell or see too much fuel in the exhaust water.

Engine serial number is?

 

[Omann68]

Hi there, welcome to iboats.

What spark plugs and plug part numbers did you put in new? Are they the same length as the old plugs?

Distributor cap cracked maybe ?

Do you smell or see too much fuel in the exhaust water.

Engine serial number is?

Hello! Thank you for the quick reply! Engine serial number 0M381522
I used the ACDelco plugs, same part number for the original plugs I pulled. I replaced the distributor cap. I see no fuel or smell in the exhaust water. Seems like I’m not getting fuel to the carb because it’s not starting but almost starts.

 

[stresspoint]

best bet is you firing order was messed up somehow .
go over the firing order again , the best way i have found to tell people is to pull all the leads , crank the motor , mark an arrow on the dizzy if you want , this will insure your are placing the leads in the correct direction.
find TDC compression on #1 by cranking and putting your finger over #1 plug hole , align the mark on the balancer with the TDC mark on the cover. place the leads in the cap and corresponding plugs one at a time.

 

[Omann68]

best bet is you firing order was messed up somehow .
go over the firing order again , the best way i have found to tell people is to pull all the leads , crank the motor , mark an arrow on the dizzy if you want , this will insure your are placing the leads in the correct direction.
find TDC compression on #1 by cranking and putting your finger over #1 plug hole , align the mark on the balancer with the TDC mark on the cover. place the leads in the cap and corresponding plugs one at a time.

Before pulling the plugs I labeled each plug to make sure they were put back in the correct firing order. 1342. It started and ran for a bit after then died and now it won’t start at all. The boat repair shop told me it might be the distributor cap so I replaced that and still same problem.

 

[stresspoint]

do the above procedure , make sure the rotor is pointing exactly to #1 lead / pin on the cap when that balancer pointer is @ TDC on compression .
the dizzy may have moved and making all your wires misaligned.
i would still be redoing the leads both plug and cap ends from scratch jusst to be sure before moving on.

 

[Omann68]

do the above procedure , make sure the rotor is pointing exactly to #1 lead / pin on the cap when that balancer pointer is @ TDC on compression .
the dizzy may have moved and making all your wires misaligned.
i would still be redoing the leads both plug and cap ends from scratch jusst to be sure before moving on.

I just did exactly that and it started like a champ! Thank you! I let it run and adjusted the idle screw and “air mixture?” screw. Is there a specific I should be tightening the screws and what is the ideal idling RPM? The same thing happened last time then I got in the water and it ran rough and finally wouldn’t start. Now I’m scared to take it on the water with my family, any other advice would be greatly appreciated!

 

[Omann68]

do the above procedure , make sure the rotor is pointing exactly to #1 lead / pin on the cap when that balancer pointer is @ TDC on compression .
the dizzy may have moved and making all your wires misaligned.
i would still be redoing the leads both plug and cap ends from scratch jusst to be sure before moving on.

Thanks again for the reply and taking time to help!

 

[Scott Danforth]

Before pulling the plugs I labeled each plug to make sure they were put back in the correct firing order. 1342. It started and ran for a bit after then died and now it won’t start at all. The boat repair shop told me it might be the distributor cap so I replaced that and still same problem.

check timing while cranking
which ignition system?

 

[stresspoint]

that's good news that its running well , now you need to set the timing """as per the manual """, if the dizzy was not moved then you probably ???? have the correct timing already ,so best let sleeping dogs be sleeping and not touch it now ( maybe check and see if it is as per manual but don't move anything yet as there may be a procedure that needs to be followed with your motor ).

messing with idle and mixture screws while the motor is on the muffs (not in the water) is never a good idea 'however " you can get the settings close enough to get you in the ball park ,
I'm guessing you would be wanting around 1000 rpm out of the water , this will most likely drop to around 750 once the motor is warmed up after a run.

once you are warmed up , set the air /fuel screw for the best smooth idle you can get , then set the idle to as close to 750 as you can get it , then check that you have a smooth transition when changing >forward /neutral / reverse IE no stalling out or sputtering trying to stall out.

 

[Grub54891]

The idle should be 650 in gear under load" in the water". It also should be unrestrained, as in not tied to dock, but I've never had an issue with it being tied up to the dock.

 

[stresspoint]

The idle should be 650 in gear under load" in the water". It also should be unrestrained, as in not tied to dock, but I've never had an issue with it being tied up to the dock.

i usually set V8 or V6 motors to 750 or close too , OP s motor may need 650.
100 RPM either way when you are going for smooth transition between shifts is not really relevant ,
i have a hand held digital tach that i rarely use as i go after the smooth shift rather than being pedantic about a 100 RPM.

 

[Grub54891]

i usually set V8 or V6 motors to 750 or close too , OP s motor may need 650.
100 RPM either way when you are going for smooth transition between shifts is not really relevant ,
i have a hand held digital tach that i rarely use as i go after the smooth shift rather than being pedantic about a 100 RPM.

Yeah, out of gear will be higher as there is no load. And shift firmly and quickly, don’t pussyfoot slowly and grind the clutch dog.