Mercruiser 140 high voltage

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
So another mercruiser problem. Everyone here has been extremely helpful but I have run into another problem. I have a 85 sea ray with a mercruiser 140. I just changed the points,cap,rotor, and installed a carb kit due to an idling issue that I still have. I started looking at the coil and noticed I am getting battery voltage on the positive terminal of the coil. I read it should be 9 ish volts. I looked at the ohms from the purple wire from the choke to the purple wire on the coil and it shows 3 ohms... Kinda confused since I thought the Resistor wire was 3 ohm... So if I have resistance through the wire why do I have battery voltage?

Also I noticed on the water my battery voltage would fluctuate.. From 12 - 14 volts and sometimes reaching as high as 17.. Is there a way I could bench test the alternator or voltage regulator or is it much easier to bring to Autozone.

I also pulled the main connector harness off and just looked for continuity between the purple wire and the harness and noticed pin 2 and 5 both had continuity... Is this correct?? I would think only one would but I cannot seem to find a correct diagram.


Thanks!!
 
Last edited:

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
The coil resistance is 3 ohms and the resistance wire is 3 ohms. The positive post of the coil is the mid point between these 2 resistances. If the points are open when you measure the voltage, the resistance of the coil is irrevelant, and so the meter will read 12 volts. If the points are closed you should see the voltage divided by the resistances, 6 volts (with the engine not running). With the engine running the meter reading will depend on the quality of the meter, the type of 'averaging' the meter is set up to do and the dwell angle of the points. What you should see it the 'average' of the full voltage (from when the points are open) and the voltage divided voltage... Hence ABOUT 9 volts. Again, depending on a lot of variables.

Alternator voltage jumping around like that could indicate a failing alternator/regulator (take it to autozone for testing) or a bad wire to the regulator (check the bullet connectors on the purple and the red/purple wires going to the back of the alternator or a bad engine ground. Check ALL ground cable, ensure they are clean and tight. Remove them and clean the cable connector, the bolt/nut head and post.... retighten and cover in grease or Corrosion Guard.

Continuity between 5 and 2 I would expect. 2 is the tacho feed wire from the negative side of the coil and 5 is the purple IGN ON wire, feeding to the positive side of the coil (via a low resistance wire). If your meter was accurate enough you should actually see about 6 or 7 ohms between them. If you are using the beeping continutiy check on the meter which only looks for a return voltage, then it will beep.

Wiring diagram attached. ;)

Chris.......

 
Last edited:

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
I will have the alternator checked today or tomorrow.. I removed it last night and the connections to the alternator were clean but i will go around the boat and check everything.

I know my meter is a cheaper Harbor freight unit so what i need to do is make sure points are closed and check the voltage and see if i have 9 volts at the coil? I will also read the ohms from pin 2 and 5 and see if i have 6-7 ohms you talked about.
 

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
Well after visiting Auto Zone they told me they would be unable to test it but i could order one through them for 95 dollars... I declined and figured i would reinstall on the boat and try testing myself. Does anyone have the process to test the alternator on the boat? I am sure since its charging just between normal and high its a faulty voltage regulator but just wanted to be sure..

I also noticed on the picture of the wiring diagram above it shows 4 studs off the alternator but mine only has 2. One where the orange was connected and the black wire is connected where a capacitor is connected to. Then the purple and red/purple are connected to bullet connectors... Did someone mess with my alternator or is this common among boats?
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
You might try a Napa or Oreily's. I don't know why autozone would say that.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Well after visiting Auto Zone they told me they would be unable to test it but i could order one through them for 95 dollars... I declined and figured i would reinstall on the boat and try testing myself. Does anyone have the process to test the alternator on the boat? I am sure since its charging just between normal and high its a faulty voltage regulator but just wanted to be sure..

I also noticed on the picture of the wiring diagram above it shows 4 studs off the alternator but mine only has 2. One where the orange was connected and the black wire is connected where a capacitor is connected to. Then the purple and red/purple are connected to bullet connectors... Did someone mess with my alternator or is this common among boats?

Are you saying the purple/red and purple are not connected to your alternator? If so, then someone has replaced it at some stage, and to have a radio suppresion cap on the back may indicate automotive. :eek:
 

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
My mistake, i should have been more detailed. The purple and red/purple are connected but if you look at the diagram more careful it appears there are 2 wires that are connected around the left and right of the alternator that do not have color labels.

I have another multimeter and with the alternator still disconnected i have 8 volts on the positive side of the coil with the motor off. All i did was disconnect the alternator and cleaned up all connections around the motor. I am wanting to connect the alternator and see if it now changes. Is it possible its was a grounding issue?
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
So if I have resistance through the wire why do I have battery voltage?
Because your points are open and you have no current through the resistor wire. Since you have no current through the resistor wire, you have no voltage drop across the resistor wire hence the reason you measure full battery voltage.

Make sure your points are closed and measure again.

EDIT: I see Chris answered this question already.
 
Last edited:

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
Well I connected the alternator back and started the motor on muffs. I noticed after some time it would bog down and the voltage would spike up to 17 volts. This caused the motor to idle rough and the coil to show 13 volts on the positive post.

I proceeded to remove the orange wire from the alternator and started it. It idled better as well as showed 8 volts on the positive post of the coil.

I believe the alternator has a faulty voltage regulator. I was able to find a 1 wire alternator for 15 dollars used. Besides taping off the purple and red/purple wires is there anything else I need to do to switch mine from a 3 wire to a 1 wire??
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
..... Besides taping off the purple and red/purple wires is there anything else I need to do to switch mine from a 3 wire to a 1 wire??

Nope. Just be sure the new alternator is MARINE rated. It should have a label on it with SAE-J1171.
 
Last edited:

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
Ok i ordered the alternator so it will take a few days. I am still having a slight miss at idle on muffs... I rebuilt the carb, plugs,coil,points,fuel filter.. And yet I still have it. I checked fuel pressure with a cheap gauge I have and it was around 4 psi.. I also checked manifold vacuum and it was around 40 but was not steady and would wiggle around some. I turned the idle mixture screw until I achieved the highest reading and it was barely in the green. Plug gap is 35 with the correct plugs and dwell is set at 28 degrees. I also checked compression the other day and when cold it was 135,150,150,140.. They don't seem that bad and I'm sure they get better when warm so what else am I missing?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Barely in the green and wiggling around sounds like worn valve guides.
 

trobin0406

Seaman Apprentice
Joined
May 31, 2016
Messages
33
How hard is it to replace worn valve guides? Would it even be worth it? I wouldn't think warn valve guides can cause rough idle.
 

Grub54891

Vice Admiral
Joined
Jun 17, 2012
Messages
5,908
Valve guides can cause it to miss, as the valve cannot seat correctly. I had an old Chevy that had a miss, When I was trying to adjust the valves, the miss would come and go on one cyl. I could hold the valve stem with a stick as it was running, and the miss would go away, let go and it would come back
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
How hard is it to replace worn valve guides? ....

Pull the cylinder head and take it to a machine shop. Is it worth it? Is up to you.... Ask a machine shop for a quote to overhaul a '4 cylinder 2 valve per cylinder cast iron head' (tell them you suspect worn guides!). Price up the new gaskets and take it from there.

Chris........
 
Top