3.0 Coil, Points Questions

[bebecker]

My '89 Mercruiser 3.0 Alpha One worked for 20 minutes and suddenly died while pulling a skier. It did have some hesitation on full throtle hole shots while getting the skier up. However, it seemed to run along fine. The engine would not restart and we were towed in.<br /><br />Thought gas, but pushing the throttle forward sends gas into the carb bowl.<br /><br />Thought spark, and the fun has began. I have been reading post after post to try and get some info, but throught I would post my own with specifics.<br /><br />I have 5.3 volts to the + side of the coil and at the "D" post on the starter solenoid where the purple/yellow wire connects when the key in in the run position. Is this normal?<br /><br />I did get spark at the points when I manually opened them.<br /><br />Any ideas where to go next.<br /><br />Thanks,<br /><br />Brandt

 

[bruceb58]

Re: 3.0 Coil, Points Questions

5.3V sounds a little too low to me. <br /><br />The reason it is the same on the starter solenoid is because that will bring it up too full 12V while you crank.<br /><br />An experiment you can do is to jumper across the resistor and see if it starts that way(temporary test). <br /><br />I can think of three possible problems. One is that your coil is going bad and drawing too much current. This will cause more voltage drop across your ballast resistor. Another is that the ballast resistor is bad(not as likely). The last is a bad connection somewhere. Measure the voltage at both sides of the ballast resistor. One reading should be identical tho the voltage at the coil. The other side should be battery voltage. If the side that should be battery voltage is low, start checking from your ignition switch back towards the engine.<br /><br /><br />If all this checks out, pull a spark plug wire and using a screwdriver inserted into the end, test to see if you can get a spark to jump to a good ground.<br /><br />If you don't get a spark, try replacing your condenser and verify that your dwell is correct.

 

[bebecker]

Re: 3.0 Coil, Points Questions

Is there a good way to test the coil? I am looking in my service manual and it basically says if it makes spark it is fine. I am looking for a way to use the volt meter.<br /><br />Thanks

 

[Bondo]

Re: 3.0 Coil, Points Questions

The Coil is going to Test Bad,... No matter How you test it,...<br />The Primary Voltage is Too Low......It Should be up around 9 Volts........<br />Try running a jumper wire from the Battery to the (+) side of the Coil,........<br />If it Doesn't Run Then,....... Replace the Coil.....<br />But,... You've Still got to find Why the primary voltage is Soo Low.....<br /><br />What's the Battery Voltage, when you're getting 5 volts at the Coil,.??...

 

[bruceb58]

Re: 3.0 Coil, Points Questions

Originally posted by Bondo:<br /> <br />But,... You've Still got to find Why the primary voltage is Soo Low.....<br />

I agree...need to make a few measurements:<br /><br />1) Battery<br />2) Ignition switch<br />3) Both side of ballast resistor if you have one.

 

[bebecker]

Re: 3.0 Coil, Points Questions

The battery voltage is 12.5V. Power on both sides of the ignition switch is 12.5 when turned to the on position.<br /><br />Help me out with the resistor. This is the purple wire running from the electric choke to the + side of the coil. Is this correct. I will check at both ends and check the resistance. But first am I correct in its location?<br /><br />Thanks for your help!

 

[Don S]

Re: 3.0 Coil, Points Questions

Make sure your points are open when you do your voltage checks, or disconnect the wires on the negative side of the coil.<br />Might also remove the gray wire (Tach lead) from the coil. If your coil shorted out, it could cause the same problem.

 

[bebecker]

Re: 3.0 Coil, Points Questions

Battery Voltage 12.5V<br />Starter Pole Voltage 12.5V<br /><br />Points open, key on, + pole of coil= 4.5V<br /><br />Removed wires from positive side(purple and purple/yellow) voltage here is 9.6V<br /><br />When I check the resistance from one end of the resistor to the other I get 0.0 ohms. This puzzeles me as the voltage here is 9.6v when removed from the coil. It must be providing resistance, yet it reads 0.0 ohms. What am I missing here.<br /><br />So does this mean the coil is bad, and probally the points, condensor, resistor?<br /><br />Thanks a million guys!

 

[bruceb58]

Re: 3.0 Coil, Points Questions

You need to remove one of the wire of the resistor to measure the resistance. You are measuring another path by doing it this way.<br /><br />Did you try removing the tach yet. Like Don said, remove the tach wires. I had a bad tach once that caused erratic behavior.<br /><br />Another thing to check is your condensor. If it has an internal DC path to ground that could also cause this problem. Just like the reisistor, you need to isolate one of it's inputs to measure it. Pull its wire off and measure from the case to the wire. Should measure infinite ohms. The other way the condensor fails is by opening up. If a condender fails in this way, the coil will always have current flowing through it while the points are closed. Normally, current only flows through the primary windings of a coil while the condensor is charging. You probably can't test for this other than putting in a new condenser.

 

[I/O WALDO]

Re: 3.0 Coil, Points Questions

Cannon plug resistance?