I haven't used my boat much this season. The engine is a '95 Mercruiser 4.3L 4bbl Carb. The last time out was 3 weeks ago. The day started off with the engine running normal but as the day progressed the engine started running poorly. I was only getting about 3500 RPM wide open whereas it usually will run to 4600. I had fresh fuel in the tank. I believe the ignition is at fault. I've since started the engine twice in the driveway with the muffs and the engine is running OK. However, there's no load on the motor so I realize I need to launch and take it for a ride to really assess how it's running. However, I hooked up a vacuum gauge and the needle is steady and in the green area. I believe the module or some other ignition component may be crapping out when it gets hot. When the motor is cooler it runs fine so I am ruling out fuel or carb related issues. It also starts right up when cool but when I was having the problem 3 weeks ago the motor was hot and being really stubborn when I tried to re-start it. I also checked for ignition spark and it seems OK in each cylinder (but I haven't check the plugs, which have about 50 hours on them) Anyone encounter any ignition system breakdowns such as what I am describing? Also, I am considering replacing it with an ignition system used on the Volvo-Penta version of this engine. That would be a lot cheaper than sticking with the proprietary Mercruiser parts.
Ignition Breakdown? 4.3L Thunderbolt IV
- Thread starter seachunk2
- Start date
Yeah, That would be the place to start. The TBIV coil is a can type coil that's filled with oil. There's a phillips screw holding the cap down. Pull the plug wire and see if oil is leaking. Also, the TBIV coil uses a full 12 volts so make sure you don't have the resistor type coil or a resistor next to the coil.
As a maintenance type procedure, pull the dist cap and scrape the posts and rotor. That toothy thingy should pass equally between the pick-ups. Just a little too much to one side can affect running.
As a maintenance type procedure, pull the dist cap and scrape the posts and rotor. That toothy thingy should pass equally between the pick-ups. Just a little too much to one side can affect running.