Reliability upgrades for 7.4l mercruiser

[Victorwithac]

Hello, so we just bought a '97 CRS Aria 3120 and it has two 7.4l mercruiser (not mag) in it. They both run well but the stbd main died out last time we were out which resulted in a broken steering cable and a tow home. I believe by yhe symptoms it is ignition related as the engine cranked healthy but the tach didnt move and no start. If the tach starts to move the engine fires no problem. It runs well but randlomly shuts down. So my question is this, is there an ignition upgrade for the engines? I just want them to start everytime i hit the key. We dont go fast and I just want reliability. I plan to cross connect the steering pumps to do away with that issue but im focusing on the engines now and then steering. I'm very mechanically inclined but mostly diesel stuff. I do know gss engines ok and boats really well. Just unsure of specifically what is suggested. I know MSD has a good following in the street world, is this the same with boats? Any insight is appreciated this is my first boat and we love it but I dont want to be towed again if i can help it. If this topic is beat to death im sorry but i didnt see anything definitive (of course there never is). Price is less of a factor than performance (reliability).

 

[NHGuy]

Welcome!
What year and model are the engines?
Carb or Injected?
I have heard that if the tach dies it will keep the engine from running on carb engines, It may also be true of EFI, I just do not know.
Keep watching here, experts will chime in.
And no,do not buy MSD, If you end up needing ignition there are better places to go. Like OE, Daytona sensors, DUI, Pertronics and others. I'd avoid Sierra too, have heard of new defects with them.

 

[Scott06]

Disconnect the tach wire (grey) at negative side of coil if tach shorts will kill ignition. When cranking do you have 12 v at positive side of coil? Check the kill switch ? No need to get a different ignition as stock merc stuff is very good. Only knock on it is cost to replace ignition module is expensive when it goes. Google troubleshooting thunderbolt ignition system you will find a step by step way to check the system.

 

[Victorwithac]

Thank you on the reccomendations thats why i ask lol. I do not know the year of the engines. The po told me they were new but of course who actually knows. They are mercruiser 7.4L, carbs, and that's about it. I know the outdrives are bravo 2 outdrives (one needs the steering pin done) that are overall working. I'll try and get on it this week and try those steps and definetly will be getting the troubleshooting steps. We just did the rotor cap, plugs, plus a couple othet things and still problems. I've read about going to electric instead of points. Is this something worth while? I do hate how difficult mine can be to start. I just need to wrap my head around these engines so I can begin to make them right.

 

[tpenfield]

Those engines are quite reliable. As stated, it is probably the tachometer that is causing the problems.

The engine has an electronic ignition, so you just need to work through the current issue and all should be good.

If you are looking for other prevention measures, I would recommend sea water strainers on the intake side of the the cooling water flow, Assuming that it does not already have sea water strainers.

 

[Scott Danforth]

welcome aboard.

it could be the ICM or the tach.

MSD would be over-kill, and the cost of a Marine MSD setup for the motor is about 5x the cost of a new distributor and wont gain you anything on stock motors running in front of a stock drive.

 

[Scott Danforth]

Those engines are quite reliable. As stated, it is probably the tachometer that is causing the problems.

The engine has an electronic ignition, so you just need to work through the current issue and all should be good.

If you are looking for other prevention measures, I would recommend sea water strainers on the intake side of the the cooling water flow, Assuming that it does not already have sea water strainers.

Ted, the power steering cooler makes a great strainer.....

 

[tpenfield]

Ted, the power steering cooler makes a great strainer.....

Yup . . . been there, done that

 

[Victorwithac]

Im replacing everything ignition related. Its not worth the time honestly to save a few hundred with the possibility something was missed. I appreciate the help with it though definetly was not fun lol. I'm sure I'll be back as im debating pulling both out over winter to rebuild the gimbles (hopefully), give the motors a real once over, manifolds/ risers, and maybe a fresh water cooling system (if I can figure out how to make it myself). Thank you all again this seems like a very good and knowledgeable community.

 

[Scott Danforth]

Unless you install a new motor, a heat exchanger is a waste of money

The crud stuck in the block will plug the non-cleanable side of the heat exchanger

 

[Victorwithac]

I've read that. I wonder though if running restore or restore plus I can't remember which does what, but one cleans rust. I use them on my 12 valves when i buy them for coolant changes.