I tried your suggestion to check all wiring connections
especially at the new switch. I did not find any bad
connections. I took the boat out the other day and ran it with
the jumper wire attached to the coil. The boat ran great for about
an hour, then it lost power again. I checked the coil and could
not touch it because it was so hot. I let the boat cool down for
about an hour and it ran great again. When I got home, I decided
to go back to NAPA and replace the coil. After looking in their
books, they show a coil for a Mercruiser 485 that requires an
external resistor. I bought a new coil and a resistor. I came
home and tried to find the resistor, but I had no luck. I pulled out
the wiring diagram that came with the boat and it does not show
an external resistor. It does show a resistor wire to the choke,
from the coil though. I checked the coil that I had replaced a
couple of years ago and it says right on it "For use with
external resistor" What do you think?? Could the wrong coil
have caused so much problems?? Do you know if the 485 requires a
external resistor?? If so where would I find mine?? Thanks again for
your continued help, I couldn't do it without you!!!
Our response:
In the future... the
jumper wire test is exactly that... a test. If run continuously, the
coil will over heat... as you found out.
This and most small
Mercruiser engines of similar type have a special wire built into the
engine's wiring loom. This "resistor wire" maintains a
reduced voltage to the coil, while the engine is running. The reduced
voltage helps reduce electrical requirements of the ignition, extends
the life of the points and condenser, and helps keep the temperature
of the coil low.
You have the correct
coil. It should be marked " For use with external resistor".
It sounds like you bought an external ballast resistor, which is often
used in place of the resistor wire. You should not need this in
addition to the resistor wire.
What you found, from
the jumper wire test, is that by artificially increasing available
voltage to the coil; your engine ran better. This means that the
engine's ignition system is not working correctly, normally.
At this point, try the
new coil and see if it works properly. If not you will have to
continue troubleshooting to find out why the ignition system is
producing low spark.
Possible causes:
* Low battery power to
the coil.
- resistor wire is
faulty
- poor ground and/or
positive connections between the battery and engine.
- Alternator isn't
working correctly and/or grounded properly
- key switch and/or
wiring loom has excessive resistance.
* Wrong/Bad coil
- coil case not
grounded properly
* Wrong/faulty points
and/or condenser
- incorrect dwell
and/or timing
- engine oil entering
distributor
* Wrong/bad sparkplugs
- incorrect gap
* Bad distributor cap
and/or wires
* Bad/wrong rotor
- rotor mismatched to
cap
Hope this helps...
*** Not quite the end of this story. Stay tuned. ***
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