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Mercruiser 5.7 2bbl starts but will not idle - need help

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Mercruiser 5.7 2bbl starts but will not idle - need help

Old 09-21-2011, 04:45 PM
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Default Mercruiser 5.7 2bbl starts but will not idle - need help

I've got a Mercruiser V8 5.7 with the Thunderbolt V ignition system

The boat starts up instantly when the throttle is open but as soon as your bring the throttle back to neutral then the engine dies.

Any ideas?

Here is a video of what is happening: http://youtu.be/IrlKw2uHJ_U
Old 09-21-2011, 05:07 PM
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Could this be the ignition control module?

Last time we took the boat out, the hull drain plug was left open in the rear and a good amount of water got it so it's possible steam or water got onto the ICM
Old 09-21-2011, 05:10 PM
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First off, the year and hours would help as well as any info on when the last tune-up was done or any other maintenance that has been recently performed.

Without more info I would guess that maybe the linkage or idle set screw are out of adjustment. There also is a shift interupter on the cable that momentarily interupts the ignition so the gears can engage. If the cable is out of adjustment this could be staying in it's interupt mode when in neutral. Those are the first things I would check.
Old 09-21-2011, 05:23 PM
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Originally Posted by prober View Post
First off, the year and hours would help as well as any info on when the last tune-up was done or any other maintenance that has been recently performed.

Without more info I would guess that maybe the linkage or idle set screw are out of adjustment. There also is a shift interupter on the cable that momentarily interupts the ignition so the gears can engage. If the cable is out of adjustment this could be staying in it's interupt mode when in neutral. Those are the first things I would check.
The boat and motor are 1997 and there are 362 hours on them.

The spark plugs and wires were just changed yesterday. I should also mention that the boat idled fine before the water got into the engine bay which was about two weeks ago.

Where can I find the shift interuptor? Also the boat dies before I get to idle. If it's under 1,000 RPMs then it'll shut down.
Old 09-21-2011, 06:06 PM
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How high up did the water get? Starter motor? Valve cover?I would just assume at that age regardless of hours that the cap and rotor also need replaceing. If it were me I would also do the module just to know that it's good. After that it starts getting expensive.

If the above does not fix you up then I would get a V/Ohm meter and check the idle air controller.

One other thought is if any of your power/battery wires or engine harness connectors got wet then there could be corrosion forming on the wires or in the connecters. Be sure to take all your grounds loose, especially the ones to the engine block and clean and tighten them.
Old 09-21-2011, 06:11 PM
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Originally Posted by prober View Post
How high up did the water get? Starter motor? Valve cover?I would just assume at that age regardless of hours that the cap and rotor also need replaceing. If it were me I would also do the module just to know that it's good. After that it starts getting expensive.

If the above does not fix you up then I would get a V/Ohm meter and check the idle air controller.

One other thought is if any of your power/battery wires or engine harness connectors got wet then there could be corrosion forming on the wires or in the connecters. Be sure to take all your grounds loose, especially the ones to the engine block and clean and tighten them.
The water got up as far as the starter, there was about 12 inches of water so just the bottom portion of the motor was sitting in it.

The starter was also replaced yesterday since the water killed it. The battery is also new.

I am getting a new module on Friday so my fingers are crossed that this is the issue!
Old 09-22-2011, 09:25 AM
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Would the shift interrupter slowly make the engine die like it does in my video? Or would it be an instant shutoff?
Old 09-22-2011, 09:51 AM
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The shift interrupter will cut the engine off the same way as turning the key does. I'm not an expert but I don't believe your ignition module is bad. I've never had a module to go bad on a boat of mine but I did have 1 go bad on a Chevy van I owned years ago. It had the HEI ignition system which is much like Mercruiser's system. It developed a problem that was taking out the modules. They were never intermittant, they either fired or they didn't. And they were not speed sensitive.

My thoughts are you are losing ignition or fuel. Or maybe it could be a timing issue as well.

Get a timing light and hook it up to any plug wire. Run the engine at it's minimum speed while pulling the trigger on light. Now get a buddy to slowly move the shifter towards neutral. Does the light quit flashing? When the engine just starts to die does it regain speed when you move the shifter forward again? I suspect it does.

If you are losing spark disable the shift interrupter switch and see if the problem goes away. Depending on model the switch could be engine mounted or in the shifter.
Old 09-22-2011, 09:55 AM
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If it's fuel related you could try this. Someone slowly move the shifter to neutral and someone else spray starting fluid into the carb. With short bursts from the can the engine will keep running even if it's own fuel supply has quit.
Old 09-22-2011, 11:44 AM
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Originally Posted by baypro21 View Post
The shift interrupter will cut the engine off the same way as turning the key does. I'm not an expert but I don't believe your ignition module is bad. I've never had a module to go bad on a boat of mine but I did have 1 go bad on a Chevy van I owned years ago. It had the HEI ignition system which is much like Mercruiser's system. It developed a problem that was taking out the modules. They were never intermittant, they either fired or they didn't. And they were not speed sensitive.

My thoughts are you are losing ignition or fuel. Or maybe it could be a timing issue as well.

Get a timing light and hook it up to any plug wire. Run the engine at it's minimum speed while pulling the trigger on light. Now get a buddy to slowly move the shifter towards neutral. Does the light quit flashing? When the engine just starts to die does it regain speed when you move the shifter forward again? I suspect it does.

If you are losing spark disable the shift interrupter switch and see if the problem goes away. Depending on model the switch could be engine mounted or in the shifter.
I'm going to need to get my hands on a timing gun to try this, I'll see what I can do.

On another note, before the water entered my boat the motor was running and idling fine.
Old 09-22-2011, 11:45 AM
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Originally Posted by baypro21 View Post
If it's fuel related you could try this. Someone slowly move the shifter to neutral and someone else spray starting fluid into the carb. With short bursts from the can the engine will keep running even if it's own fuel supply has quit.
I'll try this tonight. I am also going to pull the fuel filter to check for any water in the gas.
Old 09-22-2011, 07:03 PM
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The video acts like the shift switch. If the lower cable got wet it might be working harder causing the switch to trip.
Know that if you had the water get in that high you will be needing an oil pan in the future. Especially if it was saltwater!
Old 09-23-2011, 04:20 AM
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It could be water in the fuel. You could get a portable tank with fresh gas and try it. Troubleshooting is all about eliminating possible causes.

If water only got to the starter it shouldn't have gotten to the shift cables.

I have seen times where I developed a problem and attributed it to a recent event (water in bilge in your case) and when I finally found the cure it turned out to be completely unrelated. It was just a cowinkeydink.;?

I believe Mercruisers have several ground wires attached to the back of the block down low on the port side. It's very possible water made it up high enough to get to those. Was it saltwater?
Old 09-23-2011, 04:24 AM
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Leesfer

Post here as well, some of these guys are very good.



http://www.marineengine.com/boat-for...erndrive-Forum
Old 09-23-2011, 04:46 AM
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What drive system does that boat have, I noticed that the engine had the pulleys at the rear, is it a v-drive boat, can't be an IO, so the shift system is different than what you would have on an Alpha or a Bravo equipped boat....so there may not be a shift interrupter...
I'd try cranking it with the throttle lever in the neutral in the idle position, I wonder if a neutral switch is cutting power to the ignition...You can hook up a timing light to one cylinder, and then try cranking it with it in neutral at idle, if the light doesn't flash, that tells you no ignition....

NOW if you do have ignition after it stalls, then you have to look at other things, low speed jets in the carb, vaccum leaks, etc. I know you said this only started after the bilge was flooded, but it does start, and fast idles well, just won't slow idle in neutral.

Last edited by LouC; 09-23-2011 at 05:00 AM.
Old 09-25-2011, 04:27 PM
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Here's an update for anyone interested or having the same problem I am having.

First, my ignition sensor was wet and had gone bad causing my sparks to be intermittent.

Secondly, the carb needed to be cleaned again because it was dripping too much fuel at idle causing a bad fuel/air mixture which was the idle issue.

Everything is fixed and good to go now and I hope this helps someone else looking for this information.
Old 09-25-2011, 06:58 PM
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thanks for the follow up....so there were 2 causes not just one.....

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