Mercruiser 165 4 cylinder dies after 25 min.

I have a 1987 Mercruiser 165. I have replaced everything possible on the electrical side. New distributor(points), coil, plugs, wires, converted to an alternator, New battery, new hot battery cables etc..... have also replaced fuel pump, rebuilt carburetor, replaced fuel lines, fuel filter, etc. Thermostat, flushed cooling system, new sending unit, etc.... The engine runs like it is new...until it warms up. Thermostat says she is running at about 150 Degrees on the water side. After 25 minutes it starts to spit and sputter, then dies. Let it cool off for about and hour and it starts up and runs great again until it gets hot. I am looking for some help. I was told it could be a short, as well as it could be on the power side. The coil does get pretty warm. I have 12.58 volts at the battery and about 10 at the coil. The alternator is charging at about 13.4. It is a one wire 68 amp marine alternator. I am at wits end and ready to give up!! Any suggestions

After 25 minutes it starts to spit and sputter, then dies.

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Ayuh,..... Right at that moment,..... Is there power at the coil's (+) terminal,..??

If so, it's probably runnin' outa gas,....

There's supposed to be resistance wire going to the coil on some of those. If it's been replaced by a simple wire the voltage to the coil would be excessive (meaning it would heat up).

Jeff

Thanks Jeff, I had already replaced the resistance wire. However at a suggestion I jumped the power from the positive side of the battery directly to the positive side of the coil. The motor ran great for almost 2 hours solid. It trolled at 700 rpm, and ran great at 3500. Never ran so great!!. So here is my dilemma. By doing this it bypassed the wiring harness to the ignition, so you can not turn it off by the key. Obviously leaving the wire on is not the solution but I believe it has cut the wiring harness in half. Could this mean that I have a short on the ignition side of the wiring harness? I am going to troubleshoot the wiring harness further with my ohmmeter, however I thought I would reach out to see if someone can lead me a bit. Thanks

Sounds like the problem I had: lost voltage. I had 12 volts going to the helm, bit only 8 or 9 coming back. Chased the problem for years, then installed a relay to eliminate the problem. (Got the relay from eBay. Cheap.) It takes 12 volts right off the battery and sends it to the ignition system. The normal feed to the ignition system triggers the relay--nothing to it.

Jeff

had many issues with the coil over heating this is an internal issue and measuring voltage at the terminals most likely will show nothing out of the ordenary and causing this issue, take a spare coil with you when it stops hook it up , with jumper wires , wire tie it to the old one if it starts there is your problem, over heated coil