Engine runs perfectly for 30 minutes + then dies with no dash power

Oldnbold

Seaman
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Jun 27, 2017
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60
‘01 6.2L MPI MX. The engine 2X’s recently has run perfectly for over 30+ minutes. Suddenly it’ll stumble with an audible horn alarm, then pickup and run normally for a second ( no horn) then completely die w/o horn. I’ll have no power to the dash at all.
Battery still works as trim works and voltage with meter shows 12.6.
Next day engine starts and test runs as normal.
Where do I start my diagnosis?
 

alldodge

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Mar 8, 2009
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Check your Battery +/- cable connections from Bat thru switch and to where they connect
Also check key switch and engine connectors
 

dubs283

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5,242
Would add along with every +/- connection at battery/engine/harness to focus on the main engine harness ground connection at the flywheel cover. Should be stacked directly with the battery ground

Seen a few issues similar to yours where the harness ground wasn't touching a battery ground lead directly
 

dingbat

Supreme Mariner
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Nov 20, 2001
Messages
15,598
Temperature related failure in ignition circuit, with alarm, that resets itself with time (cool down).

Not buying a harness connection problem.
Issue with an ignition sensor/module. Need to find out what the alarm is.

Guessing you’re tripping an interlock. I’d start by checking temp switch and oil pressure sender when it shuts down.
 

Oldnbold

Seaman
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Jun 27, 2017
Messages
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Thanks for the suggestions. My original guess is a temp related ignition item like an overheated coil or my ECM going bad.
I was unaware that a bad battery connection +/- could cause my symptoms as I assumed the alternator would keep engine running.
Next up is for me to get engine to fail and start checking.
 

2003lsr

Seaman Apprentice
Joined
Apr 10, 2011
Messages
39
Check the main circuit breaker wires on top of the motor (red push button). Had a similar situation with a newly installed 350 MPI and found the small nuts for the wires to that circuit breaker had not been tightened at all. After tightening them she fired right up again.
 

cyclops222

Petty Officer 1st Class
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Mar 21, 2024
Messages
293
Classic loose and or corrode electrical connections. Could be anywhere. And more than just 1 connection heating and viabrating loose enough. Start with both big battery posts and cable clamps. Any white crud around the posts ?
Then check the place under the dashboard for loose connections. BOTH breakers & fuses. Also a place where a lot of - negative wires are screwed together. Are there any wires joined together with brightly collored WIRE NUTS used in house wiring ? Any of the ODD LOOKING auto plasticconnectors ? They can cut the wires inside of them. Drive people and mechanics crazy. Vibration and rough waves ...........ARE DEATH to all wiring in aboat................... That is all the good news I can give you for now.

Remove 1 battery cable when gently testing and pulling each wire connection. After checking the connections. Test if the boat has more trouble starting & running. Very likely. See if you can find a wiring diagram of yor boat on this forum section. You will need a lot of luck on this problem. (y)(y)
 

Oldnbold

Seaman
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Jun 27, 2017
Messages
60
Today in my testing I got the engine to fail
Several times. Initially it took 10 minutes running to go dead. After a few minutes it energized itself for a few minutes of run time.
The only consistent way to make it run/energize or fail is tugging on the battery cable at the starter. That connection is cleaned and tightened for sure as I just last week replaced the 90 amp fuse ( which currently tests ok).
However: the entire face of the starter solenoid ( where all the leads are) is not firmly attached to the solenoid housing. So when I tug on the battery cable it is moving this entire black face about 5 degrees. I’m guessing this is my problem but looking at the wiring diagram I’m failing to comprehend as to why this would kill power to 1) main circuit breaker 2) coil 3) ignition switch.
Can an expert convince me a new $300 starter with new solenoid will fix this?
 

alldodge

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Don't think that's it, my guess is there is internal corrosion in the cable it self. Remove cable and bend it around to see if you can see of feel anything loose or corroded under the insulation jacket
 

Oldnbold

Seaman
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Jun 27, 2017
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Don't think that's it, my guess is there is internal corrosion in the cable it self. Remove cable and bend it around to see if you can see of feel anything loose or corroded under the insulation jacket
During the fail time, the orange wire at the alternator is testing 12+V’s…the same as the battery. Everything else is dead.
 

alldodge

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During the fail time, the orange wire at the alternator is testing 12+V’s…the same as the battery. Everything else is dead.
You have a loose or badly corroded connection.
The ALT wire when running and if RPM is increased to 1200 RPM even once it should produce 14V or higher

If RPMs are not increased then it will read Bat voltage

Either way you have a bad connection somewhere, and yes it will be hard to find
 

Oldnbold

Seaman
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Jun 27, 2017
Messages
60
Update: found the smoking gun. The red/purple ring terminal connector at the 90 amp fuse block at the starter was intermittent.
My pulling on the battery cable was moving the loose solenoid which was wiggling the loose connection in the red/purple ring terminal. My battery cable was fine evidenced by the orange alternator wire never losing connection to the battery.
Thanks guys as without your insistence that the loose starter solenoid wasn’t the problem, I’d have simply replaced the starter w/o yanking and pulling on the bad ring terminal.
 
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