Mercruiser 4.3 Crank But no Start (spark issue)

[yahoo82]

After the battery ran down did you replace it? I had an odd situation similar to yours in that the engine would crank no problem but did not fire up. Turns out my batteries were likely damaged over the winter and although they showed 12v at rest, and they could crank the motors, the voltage drop prevented the motor from firing. I always assumed if there was enough power to crank, there was enough for ignition but I guess that’s not always the case.


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[ESully94]

I charged this battery fully (the one that the boat came with) and bought another battery with identical specs. Both batteries when on my charger read as having all cells alive and well. Brought the boat to a local marina as it’s beyond my capabilities now. Surpringly I’m not frustrated either. This is my first boat ever. And I learned a whole bunch about how it works in the process and learned how to diagnose issues. And once the mechanic tells me the issue and how he fixed it, I will be able to recognize and fix any issues I face moving forward myself

[Joey9851]

Originally Posted by mmwjr

Yes, that’s exactly what it does when shifting out of gear. It kills the ignition for a very short time to remove engine load on the dog clutch to make it easier to shift out of gear.

Would this prevent it from starting altogether? Little backstory:

Christmas 2022, we took our 2011 Bayliner out with a Mercruiser 4.3 and Alpha 1, SN: 1A633081and spent about 6 hours on the water here in Hawaii. Went out the next day, put the boat in the water and it would just turn over but never fire off. My initial thought was spark, fuel, air. I started with fuel, and drained some of the tank to see how much water was in the sample, and had a very, very thin line on the top. I replaced the fuel and water separator. Still no change. Put in a new carb, distributor, plugs and wires. Rotated the engine to TDC on compression, set the new distributor in and still no change. So then I replaced oil pressure sensor, ignition coil, and fuel pump, still no change. I just need to figure it out and it’s driving me bananas. Before anyone asks, I did check the lanyard and it’s in the run position, I’m getting voltage everywhere. This is my first boat and really want to enjoy it some more before leaving Hawaii.

[mmwjr]

Originally Posted by Joey9851

Would this prevent it from starting altogether? Little backstory:

Christmas 2022, we took our 2011 Bayliner out with a Mercruiser 4.3 and Alpha 1, SN: 1A633081and spent about 6 hours on the water here in Hawaii. Went out the next day, put the boat in the water and it would just turn over but never fire off. My initial thought was spark, fuel, air. I started with fuel, and drained some of the tank to see how much water was in the sample, and had a very, very thin line on the top. I replaced the fuel and water separator. Still no change. Put in a new carb, distributor, plugs and wires. Rotated the engine to TDC on compression, set the new distributor in and still no change. So then I replaced oil pressure sensor, ignition coil, and fuel pump, still no change. I just need to figure it out and it’s driving me bananas. Before anyone asks, I did check the lanyard and it’s in the run position, I’m getting voltage everywhere. This is my first boat and really want to enjoy it some more before leaving Hawaii.

Yes a misaligned shift interrupt switch can cause the engine from starting but I would first confirm there is spark. If you have spark then the interrupt switch is not the issue. Is this a carburetor or fuel injection engine? If carburetor you can try spraying some starting fluid in the carburetor to see if the engine will run for a few seconds. Regarding your fuel water is heavier then gas so it would be on the bottom and not the top, you may be getting phase separation that can occur with Ethanol fuel in which case the tank needs to be drained and refilled with fresh fuel.

[Joey9851]

It’s carbureted. When the issue first started, I had spark, but I don’t have spark now. Last night I went and did the test on the interrupt switch where you trim down and check the alignment of it. The y-shaped piece that moves when you shift to F or R didn’t move much at all, and the flat portions of it didn’t engage the switch. I’m really not sure where to go from here

[mmwjr]

Originally Posted by Joey9851

It’s carbureted. When the issue first started, I had spark, but I don’t have spark now. Last night I went and did the test on the interrupt switch where you trim down and check the alignment of it. The y-shaped piece that moves when you shift to F or R didn’t move much at all, and the flat portions of it didn’t engage the switch. I’m really not sure where to go from here

For the engine to run the switch roller should be centered in the valley of the shift lever. Do you have power on the ignition coil? A common ignition issue is the ignition sensor in the distributor.

[Joey9851]

I have power at the coil. The distributor is new. I’m going to look at it next weekend and make sure it’s actually in neutral. I haven’t really had time to look at it lately.

[Phillbo]

Check the kill switch at the throttle.....

[Joey9851]

That was the first thing I checked. It’s in the run position but I’m not sure if the boat is recognizing it. I finally found a mechanic to look at it next week

[Joey9851]

Originally Posted by Phillbo

Check the kill switch at the throttle.....

So I had a mechanic come out and the ignition coil was bad. Replaced the coil, but spark is weak. Using a spark tester, it’s orange when it sparks, when I would expect to see blue. I’m getting 12v at the coil when starting and 6.8v constant with key in the run position. I’m getting fuel as well. The only thing I can think of is the shift interrupt switch is bad or the module inside the distributor is bad. I’m going to order a new module and the local Mercruiser shop has the interrupt switch. I’m truly at a loss here. Is there anything I’m possibly missing?

[mmwjr]

Couldn’t the mechanic isolate why the spark is weak? I would suspect the ignition model based on all the other things you have already changed.

[Joey9851]

He stopped working on it when it wouldn’t turn over anymore. But I’ve learned that it does that when it turns over without getting ignition. I ordered the module for the distributor last night and once I get it installed, I’m going to try again. If that doesn’t fix it, I’m getting it in the shop

[mmwjr]

Sounds like either the battery ran down or the starter overheated.

[Joey9851]

I replaced the module in the distributor this morning. Still turns over but won’t fire. Getting fuel, and spark is blue so I’m thinking it’s a timing issue or the oil pressure sensor.

[mmwjr]

So you have gone from an orange spark to a blue spark, verified fuel spray in the carburetor but doesn’t run or even pop off? Even with timing being off I would expect it to pop off occasionally. Can you post a video?

[Joey9851]

It won’t let me upload the video, but essentially it just turns over without firing. It goes in the shop next weekend. I’ve basically just decided to bite the bullet and pay to get it done. I work on all my own stuff and this has me stumped

[mmwjr]

Lets us know what they find.

[Colossal Titan]

So what did you find out the issue was?