Mercruiser 3.0L required voltage - Help

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tkdm

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Jun 29, 2010
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I own a 1994 pontoon with a mercruiser 3.0L engine with EST ignition that turns over, but will not start. I check for spark at the plugs and no spark. At the battery, there is 12.43 volts. With the key on, there is 12.29 volts on both sides of the breaker. Is 11.47 volts on the purple wire going to the coil an acceptable voltage? If not, what can I check to determine the decrease in voltage? If the voltage is ok, what are the recommended next steps to triage the issue.
 
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tkdm

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Thanks for the link. I did an ohm check on the coil and pickup coil and they meet what is stated in the service manual. I spent about three hours today and haven't made any progress but I don't give up easy.

I have 11.5 volts at the coil. Is this enough? I also purchased a spark tester that contains a light. I tried it on my lawn tractor and made sure what to look for. I connected the tool to the post and touched the other end to the engine as well as the est distributor. No spark, should I see a spark? I the connected a wire from the pos term of the battery to the connector for the purple wire on the coil. I also connected the gray wire from the original harness to the coil. Again no spark out of the coil. I'm at the cottage where the boat is located. Unfortunately I don't have a trailer for the 28' pontoon so I apologize if I may sound a little desperate. Any assistance is greatly appreciated.
 
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tkdm

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The next step I tried was to connect a completely separate battery directly the the purple wire leading into the coil while leaving the other battery to power the starter. Both batteries have more than 12.40 volts. When engaging the starter the voltage to the coil remained at 12.4 volts, but no spark. I'm trying to isolated portions of the ignition system. A couple weeks back I purchased a new coil and still no spark. I completed a ohm check on the old and new coil and both were are within the spec also identical. Other posting mentioned to test the shift cutout switch. The switch has 12.36 volts going into the switch(purple wire). I am assuming the switch is open when the roller is in the middle and the post on the switch is not pressed in by the metal arm. At this position, the white and green stripe wire exiting the switch has no voltage. When I press on the metal arm that pushes the post in, there is 12 volts exiting the switch. Is this what should be expected? I understand the switch will "stalled" the engine for a brief moment so the drive can disengage but I don't understand whether the switch should ground the circuit or send 12volts the the distributor or something else?

These are some other observations.
1) The pink(appears to have a filter inline) and brown wire connecting the coil and distributor both have 12+ volts when the key. I didn't measure the voltage when engaging the starter.
2) I took the distributor cap off and did an ohm test and the results passed. I did the tests with two different meters.


Besides the questions within the above comments, I have these also
1) should there be 12volts on the post of the coil when the key is turned on.
2) can the wire exiting the shift cutout be removed from the distributor during this testing with the understanding there will be no shifting?


There is no lanyard or kill switch on this boat. 1994 Mercruiser 3.0l EST ignition.
Assistance in answering any of the questions or offering suggestions is greatly appreciated.
 
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BruKen

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Feb 26, 2014
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Measuring the resistance across the coil is not conclusive. I was fishing one day and left the key in the ignition on (to enable the fishfinder etc). According to the mech after getting back on aux. that grounded and burnt the coil out. I measured the readings and he scoffed. He was right. His 10 minute diagnosis cost more than the part. Try a new coil and see. You will always have a spare on hand if not.
 
Bt Doctur

Bt Doctur

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UntitledES_zps50e1193c.jpg
 
T

tkdm

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Jun 29, 2010
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Thanks for the replies. I have purchased a new coil and the same results. That's not to say the new coil is also bad. As for the type of ignition, the later (EST) ignition type is installed on the engine.
 
Bt Doctur

Bt Doctur

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early or late the EST system DOES NOT USE A DIST CAP or Coil. You must have the second diagram I posted, correct?
With the key "on" you need voltage at the + side of the coil
"
These are some other observations.
1) The pink(appears to have a filter inline) and brown wire connecting the coil and distributor both have 12+ volts when the key. I didn't measure the voltage when engaging the starter.
2) I took the distributor cap off and did an ohm test and the results passed. I did the tests with two different meters.

There is no pink wire in the ign system, or a brown wire. will need some photobucket pics . What did you ohm , the cap or the module?
 
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tkdm

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Jun 29, 2010
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Yes, the ignition style is what is displayed in posting #8.
Thanks for replying. I don't have pictures at this time, so hopefully this clarifies. The pink(has the filter inline) and brown wire are part of the wire harness that connects the coil(left side) and distributor(left side) as shown in posting #8. The #8 wiring diagram doesn't state the color of the wires. I ohm tested the coil and pickup coil. I took the distributor cap off to test the pickup coil. I also verified the rotor spins when the engine is turning over.
 
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