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Mercruiser 120 NO SPARK

D

Dan Shaw

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I am really having a tuff time

I am really having a tuff time figuring this out. I can't get any spark at the plugs or high voltage coil wire. I've replaced the coil and condensor and still nothing. I have a shop manual and have performed the voltage measuring tests. One of the tests says to disconnect the negative coil wire and measure voltage from the terminal to ground. Well I do have voltage present and the test result says that the distributor is shorted. Does this mean that the points are somehow shorted or the condensor? I don't understand. Help.
 
"Is there voltage on the hot s

"Is there voltage on the hot side? Check your wiring for bare spots shorting to ground. Disconnect the condenser and check w/an ohmmeter for a short. While it is off, run the test that said it is shorted again. Condensers go bad all the time even new out of the box."
 
Thanks for the response! Yes t

Thanks for the response! Yes there is voltage on the + side. Do you mean check the condensor for a short? How exactly do you do that? I have a meter but where do I put the leads?
 
how do your point contacts loo

how do your point contacts look? clean them with a bit of emery cloth folded over
 
Use the 1K ohms setting and pu

Use the 1K ohms setting and put the positive lead on the wire and the negative lead on the case. Remove the condenser from the dist. first.
 
Dan
What voltage reading do y


Dan
What voltage reading do you have at the + side of the coil with the ignition on.

Any particular reason why you didnt replace the points while you were fiddling around in your distributor ?

Cheers
Peter C
 
"Hi Peter,

I believe I had


"Hi Peter,

I believe I had about 9 or 10 volts at the positive side of the coil. Which makes sense I think because of the ballast resistors. I didn't change the points because they looked okay and had actually been changed. I do remember however one of the ballasts getting quite hot while the other one wasn't but I don't know if that means anything."
 
"Try the following:
- wire fr


"Try the following:
- wire from distributor to coil is on the minus side.
- disconnect grey tachometer wire from the minus side to check for a short from the tach.
- There is also an interupter switch attached to the shift bracket that may be causing the problem. try disconnecting 1 wire and try.
Gabriel - Dania Marine Corp. 954-927-2999
[email protected]"
 
"one of the ballasts getti

"one of the ballasts getting quite hot while the other one wasn't"

The "other" ballast resistor is open; probably your problem.
 
"Okay, I tried again to no ava

"Okay, I tried again to no avail after work today. Here are some answers to your questions:

1. There is about 5 volts on the positive side of the coil with the ignition on. There is 13 volts at the first ballast and 8 volts at the second ballast so it looks like they are doing their job.
2. There is about 2 volts on the negative side of the coil
3. The points look good and I cleaned them anyway.
4. With the condensor off I measure about 50 ohms from the negative side of the coil to the distributor casing.
5. The interupter switch was disconnected long ago.


I also made sure there was voltage on the negative side of the coil when it was cranking and there was still the two volts. I had the distributor cap off while cranking in order to look for some spark across the points but there was none. Good grief. I have replaced the coil twice and condensor already but no luck. Maybe I got a bad condensor out of the box or coil?"
 
What is the points gap measure

What is the points gap measurement? Check it and set it to specs. then reset the distributor timing.
 
"I can check the point gap but

"I can check the point gap but I don't know how to check the timing without the engine running. Irregardless, there should still be some spark across the points while cranking, no? I've tried this test on other engines before and I've always seen a little spark across the gap."
 
Dan:

5. The interupter swit


Dan:

5. The interupter switch was disconnected long ago.

Is it shorted to ground??????

All that's left to do is to check every inch of the ignition wiring by the "pull/tug method". Check the continuity of each line involved.
 
Well the interupter switch is

Well the interupter switch is completely out of the circuit so that can't be it. Gabriel thought to check that the tachometer wasn't shorted. It's connected directly to the negative of the coil so I'll try that tonight as well as check all the other wires like you suggest. Thanks Guy
 
Well the interupter switch is

Well the interupter switch is completely out of the circuit so that can't be it. Gabriel thought to check that the tachometer wasn't shorted. It's connected directly to the negative of the coil so I'll try that tonight as well as check all the other wires like you suggest. Thanks Guy
Hello Dan did you solve the problem?
 
"Okay, I tried again to no ava

"Okay, I tried again to no avail after work today. Here are some answers to your questions:

1. There is about 5 volts on the positive side of the coil with the ignition on. There is 13 volts at the first ballast and 8 volts at the second ballast so it looks like they are doing their job.
2. There is about 2 volts on the negative side of the coil
3. The points look good and I cleaned them anyway.
4. With the condensor off I measure about 50 ohms from the negative side of the coil to the distributor casing.
5. The interupter switch was disconnected long ago.


I also made sure there was voltage on the negative side of the coil when it was cranking and there was still the two volts. I had the distributor cap off while cranking in order to look for some spark across the points but there was none. Good grief. I have replaced the coil twice and condensor already but no luck. Maybe I got a bad condenser out of the box or coil?"

5 Volts on + coil is to low. Should be ~2 to 3 volts less than battery voltage. You clearly show 13 volts on battery side of ballast wire and 8 volts on coil side of ballast wire. You should see the same at coil!!!!! When engine is running and charging system is putting out 13.5-14.5 volts, the ballast keeps the voltage at ~ 12 VDC.

You need to inspect connection at ballast wire (coil side) and the wire itself for age/brittleness. and check the ring terminal and wire at coil +. Sounds like the wire is bad from Ballast to coil +


You CANNOT measure voltage on Negative side of coil. It does not work that way. The neg side of coil is used to short coil field to ground which dumps the primary side of the coil out the high voltage terminal.(Coil Wire).
 
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