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1997 4.3 Mercruiser dieseling and hydro lock

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kkuntze

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Help!

I have a 1997 4.3 Mercruiser inboard outboard in a 182 Crown Line that has been dieseling (we always run 91 octane fuel). It does it occasionally when we shut it off on the lake but does it almost every time when brining back into shore.

This last time it did it longer than usual and when we took the boat back out to start it, it just clicked.

We couldn’t get it to fire and then trailered it home. We had water in the engine that sounds like was sucked in from the exhaust manifolds. Took all the spark plugs out and shot out all the water. We hooked up the muffs and ran oil through it three different times to get all the water out of the engine. It idled well and didn’t overheat, no knocking or shaking in the engine.

I’m waiting on the new starter, spark plugs, and dipstick to come in before we compression test and see what is going on. Hoping that no piston rods were bent from when we tried starting it and it didn’t fire.

Looking for help to find the cause of the dieseling and how to make it stop. Also looking to look at any other causes of the hydro lock or what to look for before we take it back out on the water.

Any advice or help is greatly appreciated, thank you in advance!
 
kkuntze said:
Help!

I have a 1997 4.3 Mercruiser inboard outboard in a 182 Crown Line that has been dieseling (we always run 91 octane fuel). It does it occasionally when we shut it off on the lake but does it almost every time when brining back into shore.

This last time it did it longer than usual and when we took the boat back out to start it, it just clicked.

We couldn’t get it to fire and then trailered it home. We had water in the engine that sounds like was sucked in from the exhaust manifolds. Took all the spark plugs out and shot out all the water. We hooked up the muffs and ran oil through it three different times to get all the water out of the engine. It idled well and didn’t overheat, no knocking or shaking in the engine.

I’m waiting on the new starter, spark plugs, and dipstick to come in before we compression test and see what is going on. Hoping that no piston rods were bent from when we tried starting it and it didn’t fire.

Looking for help to find the cause of the dieseling and how to make it stop. Also looking to look at any other causes of the hydro lock or what to look for before we take it back out on the water.

Any advice or help is greatly appreciated, thank you in advance!
Click to expand...
When it diesels at the end it can run backwards sucking water up in engine. I think dieseling is normally from being a tad lean, running hot, or having excess carbon in combustion chambers.

What do the spark plugs look like ? What temp does it run at.


On my old 3.0 I improved it by rebuilding the carb make sure float level is right, fattened up idle mix a tad, ran seafoam down carb to soak combustion chambers, let it sit then restarted to burn off carbon. For me it typically happened after towing a skiier so letting it idle a minute to cool down before turning off helped.

Since you got water in it check oil for milk, may need to change a few times.
 
Dieter said:
When it diesels at the end it can run backwards sucking water up in engine. I think dieseling is normally from being a tad lean, running hot, or having excess carbon in combustion chambers.

What do the spark plugs look like ? What temp does it run at.


On my old 3.0 I improved it by rebuilding the carb make sure float level is right, fattened up idle mix a tad, ran seafoam down carb to soak combustion chambers, let it sit then restarted to burn off carbon. For me it typically happened after towing a skiier so letting it idle a minute to cool down before turning off helped.

Since you got water in it check oil for milk, may need to change a few times.
Click to expand...
Thank you,

The engine runs at 150 when it’s up to temp and has never overheated, we watch that closely. Spark plugs look good.

I don’t think it’s the carb because it’s runs and idles perfect but we can run something through it just in case.

We will have to let it idle down more before shutting it off and bringing it back into shore. We changed the oil and ran it three different times, all of the water is out. Just don’t want to have this happen again!
 
When you say let it idle down

What exactly do you mean.

When shift control is moved to neutral it should idle down almost immediatly.

Do you have a problem with idle?
What is your idle when in gear and no additional throttle?
 
kkuntze said:
Thank you,

The engine runs at 150 when it’s up to temp and has never overheated, we watch that closely. Spark plugs look good.

I don’t think it’s the carb because it’s runs and idles perfect but we can run something through it just in case.

We will have to let it idle down more before shutting it off and bringing it back into shore. We changed the oil and ran it three different times, all of the water is out. Just don’t want to have this happen again!
Click to expand...
mercruiser has put a couple service bulletins out on this . I believe when I had it my float level was low which will lean things out. decarbonizing with sea foam or GM top engine cleaner will help, or at least it did for me

Here is a service bulletin on it. easiest to try is fattening up the idle mix and checking timing

 
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