Mercruiser 454 dies and hard to restart

GeoffreyH

Recruit
Joined
Aug 3, 2015
Messages
2
I recently bought at 1996 Regal Ventura 6.8 with a 454 Mercruiser I/O. In general, it starts and runs without fail. Once it warms up, however, it get a little irritable. I'll retrace my steps from when I've had it out to give you an idea of what's going on:

1) After running well for 10-15 minutes, the engine bogs down, loses power, and cuts out. I didn't have any tools with me so all I could do is check for very obvious things. The engine turned over fine but wouldn't start. At some point while sitting still, I switched to both batteries because I was running down the first. I wish I had paid attention to exactly when I did this (you'll see why later). About 30 minutes after she shut down, it started and ran rough, but got us back to the ramp. When I disengaged the prop to coast in, it died and wouldn't restart.

2) Again, it had run for 10-15 minutes and the same thing happens. This time I had tools and inspected the carbs (seem to be spraying fine) and pulled the distributor cap (no visible issues). I wanted to pull a plug to check spark but couldn't due to location/heat. The battery was running down so I switched to ALL again (don't remember at what point tho). About 30 minutes after she died, it restarted only this time it ran fine. Got us back to the ramp, but again died when I disengaged the prop to coast in and wouldn't restart.

3) The boat ran fine all afternoon, but we never ran for more than about 10 minutes at a time and it had good rest between runs. The longest run of the day was back to the marina. Disengaged the prop and she died. I anchored to troubleshoot, this time using some starting fluid to eliminate a fueling problem. The starting fluid didn't make any difference at all. I switched to both batteries and it started immediately and ran and idled fine for the few minutes it took us to get it loaded. I really needed to get in or I would have stayed out to continue to troubleshoot.

A couple other things to note:
- At no time (according to the gauge) has the boat run above normal temperature.
- According to the gauge, the alternator is putting out about 13 volts.
- The batteries (both Interstate 540 CCA I think) are less than 2 years old.
- I pulled the batteries and had them tested (fine) right after I bought the boat.
- I charge the batteries at home before each time I take the boat out.
- I start and test run the boat at home (with muffs) before each trip out.
- I filled the boat with gas between incidents 2) and 3).

It could be that there are compounding issues that 1) cause it to die while running at speed, 2) kill it when I disengage the prop and 3) prevent it from restarting (the battery may be a common thread here). I'm not sure if anybody else has had problems like this, but I figured I'd ask before I tuck my tail and take it to a mechanic who will probably eat me alive with troubleshooting costs because when the boat is cool it runs fine. Any help you can offer will be appreciated!
 

GeoffreyH

Recruit
Joined
Aug 3, 2015
Messages
2
Haven't had any responses so I decided it wouldn't hurt to tune her up. Yesterday I changed the plugs, wires, cap, and rotor button. Took her out and she ran fine but the last time I started her to come in, she wouldn't start quickly with the single battery. I switched to ALL and she started and brought us in just fine (idling/running at the ramp just fine). A buddy of mine suggested that it may be early signs of the stator going bad and producing unstable voltage when it gets hot (shutting it down when it's running and not properly charging the battery so it's hard to start later). Anybody have any experience with that?
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Haven't had any responses so

Ayuh,..... Welcome Aboard,.... Sorry We missed yer post,.....

What drive is behind this 454,..??

Ya mention the Carbs,..?? What Carbs, 'n how many,..??

Do you advance the throttle when startin',..??

Have ya checked the Contents of the fuel filter for water, 'n crud,..??
 
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