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96 Mercruiser 4.3 L 4bb V-6 Vortec with Alpha One outdrive.

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cnewton700

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Put in new plugs, plug wires, dist. cap and rotor. It backfired once starting it but then started and went to a smooth idle. Sounded good. I let it run for 4-5 minutes to loosen up the oil to make it easier to extract through the dip stick tube.
Today because of the backfire, I replaced the coil. Went to start it and in less than a second the engine slammed shut, locked up. Best way I can describe it. I put a socket on the front pulley and tried turning it with a wrench by hand. Counter clockwise at first and everything turned for a few inches so I stopped and turned it Clockwise. It turned up to the point where I started the counter clockwise turn and stopped. It won't go any further. So what happened now?
 
cnewton700 said:
Put in new plugs, plug wires, dist. cap and rotor. It backfired once starting it but then started and went to a smooth idle. Sounded good. I let it run for 4-5 minutes to loosen up the oil to make it easier to extract through the dip stick tube.
Today because of the backfire, I replaced the coil. Went to start it and in less than a second the engine slammed shut, locked up. Best way I can describe it. I put a socket on the front pulley and tried turning it with a wrench by hand. Counter clockwise at first and everything turned for a few inches so I stopped and turned it Clockwise. It turned up to the point where I started the counter clockwise turn and stopped. It won't go any further. So what happened now?
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Pull the spark plugs and crank it- I'm betting water will spray out from the cylinders- they had a lot of problens in the late-'90s with water ingestion. I went to Mercruiser training in '98 and all they had was suggestions, but IIRC, the actual problem had to do with the cam and possibly with the difference in height between the water level and exhaust elbow.

Has the engine overheated? These are supposed to have a part called a shutter valve that's intended to prevent water getting past the exhaust tube.

DO NOT crank it until the spark plugs have been removed- it will kill the starter.
 
Here's a link to other discussion-

4.3L Mercruiser dieseling / run on

I know this topic has been beaten to death, but I just want to get a little clarification from the experts. I have a 2001 Mercruiser 4.3L, 2bbl Mercarb, Alpha 1 Gen 2. I, like many others, experience run on. In my case, I don't have to run the boat very hard at all to experience this. My...
forums.iboats.com forums.iboats.com

I can't believe I actually remembered the bulletin number....: Search online for Mercruiser Service Bulletin 97-17
 
jimn said:
Pull the spark plugs and crank it- I'm betting water will spray out from the cylinders- they had a lot of problens in the late-'90s with water ingestion. I went to Mercruiser training in '98 and all they had was suggestions, but IIRC, the actual problem had to do with the cam and possibly with the difference in height between the water level and exhaust elbow.

Has the engine overheated? These are supposed to have a part called a shutter valve that's intended to prevent water getting past the exhaust tube.

DO NOT crank it until the spark plugs have been removed- it will kill the starter.
Click to expand...
jimn said:
Pull the spark plugs and crank it- I'm betting water will spray out from the cylinders- they had a lot of problens in the late-'90s with water ingestion. I went to Mercruiser training in '98 and all they had was suggestions, but IIRC, the actual problem had to do with the cam and possibly with the difference in height between the water level and exhaust elbow.

Has the engine overheated? These are supposed to have a part called a shutter valve that's intended to prevent water getting past the exhaust tube.

DO NOT crank it until the spark plugs have been removed- it will kill the starter.
Click to expand...
Thank you Jimn. I pulled the plugs, turned the ign. key and it started cranking, spewing water everywhere. I live an hour North of San Diego and we just had 3 days of almost non stop rain. I didn't have the engine cover on the motor thinking I was safe with the carb. cover but noticed today that there were 2 extra holes drilled in the cover. I don't know why. Also I noticed the majority of water came out of the back two cylinders. Would having the front of the boat jacked up so rain water would drain be the reason for that ?
Thanks again.
 
cnewton700 said:
Thank you Jimn. I pulled the plugs, turned the ign. key and it started cranking, spewing water everywhere. I live an hour North of San Diego and we just had 3 days of almost non stop rain. I didn't have the engine cover on the motor thinking I was safe with the carb. cover but noticed today that there were 2 extra holes drilled in the cover. I don't know why. Also I noticed the majority of water came out of the back two cylinders. Would having the front of the boat jacked up so rain water would drain be the reason for that ?
Thanks again.
Click to expand...

How many cylinders had water? It's impossible for me to know where the crank was WRT firing order, but it woudn't appear that the bulletin applies to your engine. You would have had the dieseling/run on problem before now. If the boat was rockin' & rollin' in the slip, I would bet that it came in through the exhaust.

Water in one cylinder will prevent an engine from rotating- if you have heard people mention hydro-lock, that's what yours experienced. It's also referred to as hydraulically locked.
 
If that ‘96 4.3 still had the one piece batwing stye exhaust manifolds, these were prone to cracking due to casting problems (they weren’t getting adequate wall thickness) and therefore they are known to let water into the cylinders. Get the water out of the cyls and change the oil. Test the manifolds off the engine by hooking up a water source.
 
Both Mercruiser and Barr Marine make a kit to convert these engines to a conventional 2 piece manifold/elbow exhaust system without changing the exhaust Y pipe….
 
After cranking the water out I put a small amount of oil in each plug hole, cranked it again for a few seconds and re-inserted the plugs. Half hour later I turned the key and it instantly started up. I ran it at 1300 rpms a few minutes and backed it off to an 650 rpm idle for about 5 minutes. It ran very smooth, no misses, hiccups or shaking at all. I shut it down and about an hour later it fired up again without incident. It almost feels like I'm done but I know better. I'll just say so far so good. And that I appreciate the hell out of you all for your advice and going out of your way to help.
Until next time, thank you so much.
 
cnewton700 said:
After cranking the water out I put a small amount of oil in each plug hole, cranked it again for a few seconds and re-inserted the plugs. Half hour later I turned the key and it instantly started up. I ran it at 1300 rpms a few minutes and backed it off to an 650 rpm idle for about 5 minutes. It ran very smooth, no misses, hiccups or shaking at all. I shut it down and about an hour later it fired up again without incident. It almost feels like I'm done but I know better. I'll just say so far so good. And that I appreciate the hell out of you all for your advice and going out of your way to help.
Until next time, thank you so much.
Click to expand...
Get it run up to temp and check oil for milkyness as you may have gotten water in the oil via the rings. If you do have milk in the oil you will need to change it until it is clear otherwise it will rust inside engine .
 
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