7.4L 454 Mercruiser engine cuts out / Stalls

[TGunn]

Hello, I am new to the Forum and looking for some wisdom on my problem. I have a 1987 Baja Force 320 with twin 7.4L 454 Mercruiser stern-drive engines. Recently the starboard engine cut out at about 45 mph. I did get back to the Marina limping on just the port engine. However I was able to re-start the starboard engine for a while and get the boat docked. This past weekend I changed water separator filters on both engines and replaced the ignition coil on the starboard engine. But, I'm having the same issue with the engine cutting out after 2 or 3 minutes. Additionally, when the ignition key is turned on the engine does not always turn over - this is intermittent. Previously, I replaced the slave solenoid on both engines when the ignition key was turned but no engine start at all. Again the engine will now eventually turn over and start but still cuts out after a few minutes. My next guess is that it could be the TB-IV ignition amplifier module? But would a TB-IV ignition amplifier module fail intermittently and cause the engine to stall out? Or perhaps this is a carburetor problem or bad ground or some other wiring issue?

 

[Scott Danforth]

first, welcome aboard

second, follow the troubleshooting guide on TB ignition in the manual. it is also in the stickies

third, its never the coil. I really need to buy stock in a coil company because about a million coils are changed every year and legitimately only about 3 are ever bad.

4th, sound more like bad connections...... start at the battery and clean every battery connection with 150 grit sand paper. by clean, shiny enough your mother would eat off it clean. then after you tighten the connection, seal it with marine electrical varnish. if your battery cables look iffy, replace them. clean the ground terminal on the block. and work your way up the harness to the helm cleaning the pins and terminals at every connection.

 

[tpenfield]

:welcome: to iBoats . . .

Post the serial number of the engines for best input, but I assume, based on the year (1987) they are the carbureted Mark VI version of the 454.

I would check the ignition switch and kill switch to see if you are sending 12V back to the ignition system, particularly when the engine dies. Don't keep throwing parts at it without some diagnostic work, unless you have plenty of money.

 

[TGunn]

Scott and Ted, I appreciate your advice! The Starboard engine is indeed a carbureted MCM 454 Magnum, with serial number "B 428422". it seems you are both indicating is it some sort of electrical connection, battery, or ignition/kill switch issue?

 

[Scott Danforth]

we are indicating where to start your troubleshooting based on what limited information you have provided.

 

[tpenfield]

we are indicating where to start your troubleshooting based on what limited information you have provided.

Yes, a process of elimination . . . since there are so many things that it could be. . . . and boats like to mess with ya . . .

 

[TGunn]

Update: Went through all of the electrical connections starting at the ignition key down to the battery and engine. Used a wire brush, steel wool, and sand paper to get all connecting surfaces clean & shiny. Then tightened all connections and sealed it with marine electrical varnish. She started up and ran fine! Kept the engine running with muffs for about 10 minutes, no problems. Then turned the engine off and on several times to verify no intermittent starting issues with the ignition switch. I’ll take the boat out on a test cruise soon, but it seems my electrical continuity problems were solved with some elbow grease…. Appreciate everyone’s input. Thanks!