5.0 Mercruiser Cutting Out While Underway

[MadSANMan]

I have a 2003 Bayliner with a 5.0 Mercruiser. I am having trouble that appears to be ignition related. It's progressively gotten worse throughout the past couple of days. It started out as a brief loss of power while underway at pretty much any RPM. It''s as if someone threw a switch to kill the engine and then through it back again. Most times, it would continue running. It would do this about once a minute. I started looking at the ignition components... the distributor cap was pretty bad so I cleaned it with some ScotchBrite. It seemed like the more I did to cleanup the mess, the worse the symptoms got. Now it's not starting so I'm at a loss as to what to try next. I should also mention that the tach was reading incorrect RPM when it was running. It was usually reading too high. I had the engine running at roughly 1200 RPM by ear and the tach was jumping between 2400 RPM and

 

[MadSANMan]

I have a 2003 Bayliner with a 5.0 Mercruiser. I am having trouble that appears to be ignition related. It's progressively gotten worse throughout the past couple of days. It started out as a brief loss of power while underway at pretty much any RPM. It''s as if someone threw a switch to kill the engine and then through it back again. Most times, it would continue running. It would do this about once a minute. I started looking at the ignition components... the distributor cap was pretty bad so I cleaned it with some ScotchBrite. It seemed like the more I did to cleanup the mess, the worse the symptoms got. Now it's not starting so I'm at a loss as to what to try next. I should also mention that the tach was reading incorrect RPM when it was running. It was usually reading too high. I had the engine running at roughly 1200 RPM by ear and the tach was jumping between 2400 RPM and 1200 RPM. I'm vacationing in the north woods of Wisconsin so my access to parts is limited. I also launched the boat from trailer at a launch about a mile from here and as it is now, I do not have a way to retrieve the boat. Any advice would be appreciated. Thanks, JC

 

[Rick Stephens]

Disconnect the grey tach wire from the coil, try it again. See if the tach is shorting.

You have the crab style disty cap? I'd replace it.

DIsconnect and reconnect your man overboard lanyard. Make sure it is making correct connection.

If that doesn't get it, put a voltmeter on the purple wire at the motor end - can be at the choke or ignition. See if the voltage is dropping when the engine misses.

 

[flashback]

All the above and also put a new water separator filter on it. Water in the fuel can cause some very erratic stop and go symptoms..

 

[Scott Danforth]

Is your distributor trigger have 2 wires, or is it the new 3-wire design,m

 

[MadSANMan]

Is your distributor trigger have 2 wires, or is it the new 3-wire design,m

It has two wires.

 

[MadSANMan]

Disconnect the grey tach wire from the coil, try it again. See if the tach is shorting.

You have the crab style disty cap? I'd replace it.

DIsconnect and reconnect your man overboard lanyard. Make sure it is making correct connection.

If that doesn't get it, put a voltmeter on the purple wire at the motor end - can be at the choke or ignition. See if the voltage is dropping when the engine misses.

How do I know if I have a crab style distributor cap?
I'm still on vacation and we had to pull the boat from the water so I'll try you suggestions when we get home. Thanks!

 

[MadSANMan]

One other thing I forgot to mention is that when the engine died while underway, it almost always immediately restarted without any hesitation.

 

[MadSANMan]

All the above and also put a new water separator filter on it. Water in the fuel can cause some very erratic stop and go symptoms..

I should've mentioned that this was the first thing I tried.

 

[Scott Danforth]

It has two wires.

Most likely going south. New design is 3 wire

 

[alldodge]

What is the motor serial number?

 

[MadSANMan]

What is the motor serial number?

0M616574

 

[MadSANMan]

Most likely going south. New design is 3 wire

I found the part for the new 3 wire trigger. Is it a direct replacement for the 2 wire design or do I need to upgrade any of the other ignition components?

 

[alldodge]

Thanks for the SN
You have a TBV (no flat cap) and either a TKS or Merc carb
The 3 wire is direct replacement and no need to upgrade other components

 

[MadSANMan]

Does anyone feel that the source of the problem is the ICM or is that the least likely culprit?

 

[alldodge]

The issue is electrical. Motor cuts out and back on wouldn't be fuel.

Being electrical it can be a bad connection ground or hot side, key switch and pretty much anywhere there may be corrosion. There have been a lot of trouble with the 2 wire modules and this is why Merc changed it.

No one can say the IC module is doing it, just it has a high probability.

If you have checked key switch, wires connected to it and others, dizzy and components in it, then its as narrowed down

 

[alldodge]

Oh and no need to buy Merc module, can get it from auto parts store

 

[MadSANMan]

Oh and no need to buy Merc module, can get it from auto parts store

I searched for an ICM for small block Chevy/GM 305 and got a lot of different options. Is there one that is a direct replacement (connectors the same) as the Merc?

 

[Scott06]

I searched for an ICM for small block Chevy/GM 305 and got a lot of different options. Is there one that is a direct replacement (connectors the same) as the Merc?

Pretty sure yours is the Thunderbolt V ignition, not the Delco EST that is available at auto parts stores. The module will only be available through merc, and looks to be discontinued.

Electrical Components for Mercruiser (5.0l / 5.7l Sterndrive) Engine

www.marineengine.com

Have had good luck find them on ebay used. Otherwise if you need an ICM and cant get one a lot of folks will tear out the merc TBV and go back in with a Delco est complete set up

 

[alldodge]

I searched for an ICM for small block Chevy/GM 305 and got a lot of different options. Is there one that is a direct replacement (connectors the same) as the Merc?

Sorry my bad, I do not think nor do I think anyone else thinks (speak up if your opinion differs) your TB module is defective. I also was think ing about the EST module when I said auto store.

So back to your question: the TB dizzy module is where "I" think may be the issue.
https://www.walmart.com/ip/Quicksil...6?wmlspartner=wlpa&selectedSellerId=100001500