Need ideas on problem with 5.7L Mercruiser shutting down

[NuthinFancy]

I have a 1996 270 Sundancer with a 5.7L Mercruiser. It was running perfect for a half hour at 500rpm off max and shut down with no warning and would not turn over. Temp and all electrical was good. 3hrs later started with no prob and after 10 minutes at dock, re-started with no prob. I suspect some sort of prob with auto-shutdown temp sensor. Any ideas are welcome.

 

[stresspoint]

? why are you running your motor @ 500 RPM for so long.
V8 motors don't like that .
if you are going to be idling for such long periods , up the isle to around 750, 800 RPM with fast idle on the shifter, that should overcome your problem.

 

[NuthinFancy]

? why are you running your motor @ 500 RPM for so long.
V8 motors don't like that .
if you are going to be idling for such long periods , up the isle to around 750, 800 RPM with fast idle on the shifter.

Hi Stresspoint,
As I said: 500rpm off MAX...so around 3,900r's. Sorry for confusion and thanks for reply.

 

[Scott Danforth]

there is no auto-temp shut-down sensor.

you have an electrical problem.

does your ignition sensor still have 2 wires or was it upgraded to the 3-wire sensor?

How Mercruiser Thunderbolt ignition systems work.

Mercruiser Thunderbolt ignition systems. Mercruiser introduced the Thunderbolt IV onto their engines in 1982, alongside the introduction of the 1-R drives. The TB-IV system was used until the introduction of TB-V mid-way through 1996. Thunderbolt V was an improvement on an already exceptionally...

forums.iboats.com

 

[alldodge]

shut down with no warning and would not turn over

Have a bad connection which may have heated up and broke connection, and may be hard to find. Going to need it to do it again to find issue most likely.

When key is turned on did gauges turn on or hear anything?

 

[stresspoint]

Hi Stresspoint,
As I said: 500rpm off MAX...so around 3,900r's. Sorry for confusion and thanks for reply.

ha ha , no problem ,i miss read the post so my apologies as well.

check the big engine harness plug , check key switch , check MOB key jigger is locating properly.

 

[Scott06]

If it didn't turn over I would suspect you dropped 12v to that engine would start with cleaning and tighten both positive and negative battery connections. IF it happens again try and jump the starter solenoid to confirm if issue is wiring up to helm or is in engine harness. Would also remove the cannon plug clean corrosion and make sure the pins are fat enough to make good contact you sometimes need to tweak the pin to make good contact

 

[QBhoy]

Hi. I suspect that your charging system isn’t working. Means your engine is trying to run on battery power alone. Unsustainably. Then the battery recovers enough after a whole…enough to start it..then perhaps run for a while. Check your alternator output. Check the charge getting to the battery with some moderate rpm enough to what should see a charge coming back to it. Check your grounding cables and battery connections in general. Almost certain that the issue is related to this sort of thing.

 

[NuthinFancy]

there is no auto-temp shut-down sensor.

you have an electrical problem.

does your ignition sensor still have 2 wires or was it upgraded to the 3-wire sensor?

How Mercruiser Thunderbolt ignition systems work.

Mercruiser Thunderbolt ignition systems. Mercruiser introduced the Thunderbolt IV onto their engines in 1982, alongside the introduction of the 1-R drives. The TB-IV system was used until the introduction of TB-V mid-way through 1996. Thunderbolt V was an improvement on an already exceptionally...

forums.iboats.com

Thanks Scott. I'll check it out as you said.

 

[NuthinFancy]

Have a bad connection which may have heated up and broke connection, and may be hard to find. Going to need it to do it again to find issue most likely.

When key is turned on did gauges turn on or hear anything?

When I turn the ignition on when no prob, there is an loud tone until you start engine. When it wouldn't start, there was nothing audible, but gauges and all electrical, including windlass as i anchored waiting on tow boat, worked with no prob. Later, it started with absolutely no prob.

 

[NuthinFancy]

Thanks Scott. I'll check it out as you said.

Is the ignition sensor near engine or near the ignition key-switch?

 

[Scott Danforth]

Is the ignition sensor near engine or near the ignition key-switch?

It is in the distributor

 

[NuthinFancy]

It is in the distributor

Thanks Pal. The pics with explanations are enormous help...I'll get to the boat tomorrow and replace the sensor. If I have the old type, is it as simple as replacing it with a 3-wire, or should I stay with the 2-wire?

 

[Scott Danforth]

the 2-wire were problematic, which is why the 3-wire design came out back in about 2003

 

[NuthinFancy]

If it didn't turn over I would suspect you dropped 12v to that engine would start with cleaning and tighten both positive and negative battery connections. IF it happens again try and jump the starter solenoid to confirm if issue is wiring up to helm or is in engine harness. Would also remove the cannon plug clean corrosion and make sure the pins are fat enough to make good contact you sometimes need to tweak the pin to make good contact

Thanks...will do.

 

[alldodge]

When I turn the ignition on when no prob, there is an loud tone until you start engine. When it wouldn't start, there was nothing audible, but gauges and all electrical, including windlass as i anchored waiting on tow boat, worked with no prob. Later, it started with absolutely no prob.

With gauges turning on means power from key is working

No loud tone (alarm) means a connection to the motor is missing. Key sends power thru the 10 pin connector to motor. With no alarm this says the oil pressure switch has no connection coming back thru the 10 pin connector. Unable to crank the motor means most likely, no connection thru the 10 pin connector

As stresspoint mentioned, I would look first at the 10 pin connector

 

[NuthinFancy]

Hi. I suspect that your charging system isn’t working. Means your engine is trying to run on battery power alone. Unsustainably. Then the battery recovers enough after a whole…enough to start it..then perhaps run for a while. Check your alternator output. Check the charge getting to the battery with some moderate rpm enough to what should see a charge coming back to it. Check your grounding cables and battery connections in general. Almost certain that the issue is related to this sort of thing.

Thanks. This will be the fastest thing to do. I have received a lot of responses on this and appreciate them...one of them is bound to work. If it isn't charging, I can probably run it in the slip for a half-hour or so and see if it dies.

 

[NuthinFancy]

With gauges turning on means power from key is working

No loud tone (alarm) means a connection to the motor is missing. Key sends power thru the 10 pin connector to motor. With no alarm this says the oil pressure switch has no connection coming back thru the 10 pin connector. Unable to crank the motor means most likely, no connection thru the 10 pin connector

As stresspoint mentioned, I would look first at the 10 pin connector

Where is the 10-point connector?

 

[Scott Danforth]

Not charging is a completely different issue.

 

[NuthinFancy]

Not charging is a completely different issue.

10-4.