1997 mercruiser 3.0LX starts then dies

[CPro]

I have been dealing with a little bit of a strange issue with my 1997 3.0LX with an Alpha One. The boat starts great - like on the first crank, but once the choke opens up (which I can detect by the change in engine noise) the engine begins dying out. I have to throttle up a good bit past idle to have a chance of keeping it running. The issues began developing last year, and the fishing was so good that I just kept running the boat instead of addressing it then. I tried adjusting the idle mixture valve and I think that may have helped a little, but I know it is running too rich when I do this. I replaced spark plug wires and the ignition coil and verified the carburetor float settings. The spark plugs are pretty well black colored from carbon. Since the issues start once the engine warms up, I'm thinking it is a fuel delivery issue of some sort. The fuel filter on the carb is new as is the fuel water separator. In the process of pulling the plugs to check them one of them broke, so that is another thing to fix before I fix the main thing that I was hoping to fix...! I'd love to hear any suggestions on possible causes of the engine dying out once it warms up. Thanks!

 

[achris]

When confronted with problems like these, I always run through a 'tune-up' list first, eliminate anything 'obvious', then start diving into the problem if it still exists.

Standard troubleshooting for an engine.

Engines require certain things to operate properly... Basically they need the correct fuel/air mixture to be compressed and then fired at the right time.

So, in this order.

1. Compression tests.
2. Check spark plugs, replace if needed.
3. If points, replace, along with condenser and rotor. Check and adjust, if needed, points cam dwell angle.
4. Inspect distributor cap, rotor and leads, replace if necessary.
5. Check spark quality (needs to be a nice BLUE spark drawn over 1/2").
6. Set timing. Check timing advance is working correctly.
7. Check/change fuel filters and check that the fuel system is not sucking air.
8. Check fuel pump pressure.
9. Check for full opening of the carb. Also ensure choke is opening fully when the engine is warm.

When all of these items have been done, THEN move to the fuel system....

You can have the best, cleanest carburettor in the world, but if the compression's low and/or the ignition system's not doing its job, the engine will still run like crap.....

Chris.........

 

[CPro]

I replaced the plugs, plug wires, ignition coil, distributor cap, & rotor. That definitely improved things but I still have an issue with surging at low speeds. Also, I have had to increase the idle speed and richen up the mixture in order to keep it idling successfully. At low speeds it will just die out. At high speeds it runs great (it gets up to around 30 mph which is about the max for that boat). I usually troll at around 3 mph when fishing and the boat seems to want to go 3.5-4 in order to keep running. I can feel it stumbling and surging a bit at these lower speeds. The carb is opening all the way up when hot. I am still working my way through the list above and I figure I'll mess with the timing next. This should be interesting since the timing indication mark rusted away years ago. Can I time the engine effectively just by sound?

Also, I'm expecting that based on all the rust that has popped up on the side of the engine block it's time to do the head gasket. I can also see small beads of water along the upper lip of that plate that is on the side of the block. Please let me know if you have any thoughts on this...

Thanks!

 

[achris]

I replaced the plugs, plug wires, ignition coil, distributor cap, & rotor. That definitely improved things but I still have an issue with surging at low speeds. Also, I have had to increase the idle speed and richen up the mixture in order to keep it idling successfully. At low speeds it will just die out. At high speeds it runs great (it gets up to around 30 mph which is about the max for that boat). I usually troll at around 3 mph when fishing and the boat seems to want to go 3.5-4 in order to keep running. I can feel it stumbling and surging a bit at these lower speeds. The carb is opening all the way up when hot.

That sounds like the carb needs to be pulled, stripped and cleaned out. Then reassembled to spec.

I am still working my way through the list above and I figure I'll mess with the timing next. This should be interesting since the timing indication mark rusted away years ago. Can I time the engine effectively just by sound?

Definitely not!

Also, I'm expecting that based on all the rust that has popped up on the side of the engine block it's time to do the head gasket. I can also see small beads of water along the upper lip of that plate that is on the side of the block. Please let me know if you have any thoughts on this...

Thanks!

I'm curious about the silicone around the spark plugs....

Chris......

 

[CPro]

I recently rebuilt the carb. I pulled it apart again a couple days ago to check the float level, etc and I'm reasonably confident it is not a carb issue (although i could certainly be wrong). The stuff around the plugs is dielectric grease. Corrosion was getting in around the plugs and i wanted to keep moisture away from them so i gooped them up. What aboug all the rust on the side of the block? Does thst indicate it's time to do the head gasket?