Mercruiser 140 ignition coil voltage

Status
Not open for further replies.

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
What should the voltage be when taken on both sides of the coil? I have read until I am blue in the face, including the sticky, and I am still confused. Admittedly, I get my cookies from the low shelf on this stuff. I get readings of 10.5 on the + side and 6.5 on the - side.
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: Mercruiser 140 ignition coil voltage

If it has points the 10.5v is OK. Post up a serial number so people know what you are working on.
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

Serial #6853440. It has Pertronix electronic ignition.
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: Mercruiser 140 ignition coil voltage

Is the coil a standard coil? The Pertronix units should see a full 12v.
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

It has a Pertronix coil that was added about a year ago with the other ignition components. With this set up, can I just run a new wire from the battery (+) to the coil or from another (+) source, or will that do something bad, like set my boat on fire?
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: Mercruiser 140 ignition coil voltage

With this set up, can I just run a new wire from the battery (+) to the coil or from another (+) source, or will that do something bad, like set my boat on fire?

Your Pertonix setup will want the full 12v - not the reduced voltage available if you originally had points. Yes you can, and should, bypass the original "resisted" wiring. You will need to tap into a switched 12v line. If you have an electric choke, that is a good source to tap into.
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

Thanks very much. I'll report back.
 
Joined
Sep 30, 2013
Messages
18
Re: Mercruiser 140 ignition coil voltage

You need to be careful the 4cyl engine has specific requirements when it comes to coil resistance. In addition the Pertronix Ignitor I is different from the Ignitor II.

The Points and Condenser or Ignitor I installations require a coil with 3.0 ohms of internal resistance or you need to have either an external resistor or resistance wire upstream of the coil.

If you have a resistor the Ignitor red wire hooks to the wire feeding the resistor and the black wire hooks to the (-) side of the coil. Based on your readings it looks like you may have a coil with internal resistance but to be safe you can check it easy enough.

Check the resistance of your meter- touch the red lead to the black lead and write down the number ie .2
With all wired disconnected from the coil touch the red Lead to (+) side of coil Black lead to (-) side subtract the number above from the reading and you have your coil's resistance. Or if you can find your coil's part number see below. The coil for a 4cyl engine with no external resistor should be 3 ohms.

Flame-Thrower? (Pertronix) Coil Primary Resistance:

40001 1.5 Ω (oil-filled)
40011 1.5 Ω (oil-filled)
40111 1.5 Ω (epoxy-filled)
40501 3.0 Ω (oil-filled)
40511 3.0 Ω (oil-filled)
40611 3.0 Ω (epoxy-filled)


Do not use any other Flame-Thrower? coil, as it won't have enough primary resistance, allowing too much amperage to flow to the ignition module, destroying the module or shortening its life. (except if you have the Ignitor II)

As Fishermark stated above the red wire from the Pertronix unit/ distributor needs clean switched 12 volt power. Be careful about hooking up to an electric choke I have heard that you could see reduced voltage during cold starts. If the power to the coil does not shut off when key is shut off you will fry the internal parts.

I know you do not have a Hot-spark but these guys do a good job explaining the whats-it and why-fors
Compatible Ignition Coils, Ballast Resistors, Hot-Spark Electronic Ignition
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

I have a 3.0 ohm coil. I will try a switched 12 volt supply and see what happens. Thanks very much. Don't forget that I get my cookies off a low shelf when you start talking about volts and current and ohms and resistance and whatnot.
 
Joined
Sep 30, 2013
Messages
18
Re: Mercruiser 140 ignition coil voltage

Hold up boozer.
Before you start chasing sparky around your boat with new wire let's review a few things:
We have confirmed that you have the proper coil for a 4cyl 140 without an external resistor.
You have indicated that you have a Pertronix coil. True?
Are you sure that you have the Pertronix module installed in your distributor?
How many wires are coming out of your distributor? 1 wire = points and condenser. 2 wires = Pertronix conversion.
When you checked the voltage at the coil was the battery fully charged?
OR
When you checked the voltage at the coil was the motor running?

You need to confirm all of the above before making any changes since if you do have a Pertronix conversion that was properly installed the wire that you intend to run has already been run as part of the conversion.

What is the actual problem that you are trying to solve?
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: Mercruiser 140 ignition coil voltage

Here's what your setup should look like:

pertronixwiringdiagram.jpg
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

Many thanks to all. I have been trying to trace down an intermittent ignition short or ground problem. Boat starts and runs on muffs without problem, then for about 45 minutes on the water before going haywire, usually at the worst possible moment. Boat will sputter and die. Restart and run rough. It's definitely electrical. I have traced, cleaned and tightened just about every electrical connection on the boat. I now have 12 volts at the coil with the engine running. I will report back. Again, thanks for all y'all's help.
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: Mercruiser 140 ignition coil voltage

How are you sure it is electrical?
 
Joined
Sep 30, 2013
Messages
18
Re: Mercruiser 140 ignition coil voltage

Take a look at the picture that Fishmark was kind enough to post and tell us if you have confirmed that you actually have a Pertronix module installed in the distributor.
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

It is a Pertronix. I installed it less than a year ago. I am going out today to see if the offending behavior recurs after a night of cleaning, tightening and reconnecting. If it does, I will check the voltage at the coil and report back.
 

boozer1966

Petty Officer 2nd Class
Joined
May 7, 2012
Messages
125
Re: Mercruiser 140 ignition coil voltage

Just got back from the lake. Boat ran perfectly. Proper voltage at the coil. Hopefully it will stay that way. Thanks again for all the comments and suggestions.
 
Status
Not open for further replies.
Top