Merc 140 no spark...

[JoeD1988]

Just got this boat. Took it in as a project to keep me busy. Been trying to get the motor to start, but found that I am not getting spark. I have 12.3 - 12.5V on both terminals of the coil, but nothing to the plugs and nothing to the distributor. I think there is some wiring gremlins at work here but I am having trouble finding a wiring diagram. As it sits now, on the left side of the coil (if you are facing the coil) there is a wire coming from the starter, and a wire coming from a white block(the resistor?? sorry guys, don't know what it is called). On the right side of the coil, I have the black wire coming off the distributor, and a brown(possibly a different color, it's faded) going into the main wiring harness. On the white block thing (again, sorry guys, I'm sure I sound like an idiot) where the wire goes to the coil, there is another wire coming off of that same terminal that is just loose, I think that may be the issue, but not sure. Any help is greatly appreciated.

 

[Don S]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

Put some new points and condenser in it (aka a tuneup). The points corrode and glaze over in time.

 

[JoeD1988]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

Hello. I am an idiot.

 

[Don S]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

I'm not getting any spark out of the coil wire itself when removed from the distributor.

The distributor is what makes the coil spark ................ :facepalm:

 

[Don S]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

Click on the link below, then go to items 17,18,19


http://forums.iboats.com/mercruiser...tdrives/adults-only-no-exceptions-288430.html

 

[JoeD1988]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

The distributor is what makes the coil spark ................ :facepalm:

Now I feel like an idiot, LOL. I am not very educated when it comes to ignition systems, obviously. New points, condenser, rotor button and distributor cap are in the works. I'm just worried about the wire coming off of the resistor, I'm sure it goes somewhere.

 

[Don S]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

Merc hasn't used a Ballast resistor since the 60's. Might want to post a picture of what you have. Could be a previous owner "Fix" that isn't by the book. So we would have no clue what you have.

 

[JoeD1988]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

It's definitely not original to the motor. Notice on the bottom terminal there are 2 wires coming off of it. One goes to the coil, and one is just hanging out....

 

[Don S]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

Here is how it should be wired, and yes that "white thing" is a ballast resistor. You have to trace the wires, it's anyones guess except the one that insalled the thing what they did.

Wire color codes are probably not the same, you have to follow them and see where they go.

 

[JoeD1988]

Re: 1986 Merc 140 no spark...

Re: 1986 Merc 140 no spark...

Thank you for the diagram, will begin to trace wires down after work tomorrow. Just from memory comparing to the diagram, I can already see that some of the wires are not in their correct places.

 

[JoeD1988]

Re: Merc 140 no spark...

Just want to clarify the year of the motor is not an 86, from what I can gather it is an earlier motor. Noticed this because I am having trouble finding a tune up kit, the sites that I've tried do not recognize my serial number. Serial number is 5212793.

 

[JoeD1988]

Re: Merc 140 no spark...

I've traced all the wires down, and everything looks the same except for the resistor circuit. On the resistor circuit in my case, the wire at the top of the resistor is wired into the main harness (to draw its power I'm assuming) and the wire at the bottom of the resistor goes to the side of the coil opposite the distributor wire. I don't seem to have a killswitch, so no wire for that. With the key on, I have 12V at both sides of the resistor... I'm not sure if it being wired this way would work, but I went through with the troubleshooting guide from the link in post 5 and these are my findings..

Hooked my spark tester to the tower on the coil and cranked the motor... No spark.

Disconnected all wires from coil, and checked for continuity/ohms between the tower of the coil and both terminals of the coil, nothing on either. Checked for continuity/ohms between the 2 small terminals on the coil and get 1.7 ohms.

Re-connected all wires and checked for voltage on the coil and both small terminals have 12V.

 

[Bt Doctur]

Re: Merc 140 no spark...

remove the wire from the neg side of the coil, turn key on, take a jumper from the neg side of the coil and scratch the other end to a good ground. coil should produce spark.
report findings
hookj a ohmeter to the black wire you took off the coil that went to the dist, spin engine. needle should move between infinity and 0 ohms. if it does points are working. if it dosent move ,points are not making good contact together and you get no spark.
report findings

 

[JoeD1988]

Re: Merc 140 no spark...

I removed the wire from the neg. side of the coil, attached a jumper and when I scratched it against a ground, I got a spark out of the end of the jumper, nothing out of the tower of the coil.

Where would I hook the other lead to on the meter to check the points?

 

[Bt Doctur]

Re: Merc 140 no spark...

black lead of meter to ground, red lead to the wire you took of the coil..if the points are closed you will see the needle move to the right. If they are open you will see nothing untill you crank the motor over. then the needle will move as the points open and close.

 

[JoeD1988]

Re: Merc 140 no spark...

Meter did not move while cranking.

 

[Bt Doctur]

Re: Merc 140 no spark...

needle stays to the left = points are staying open for some reason, wire to dist if bad, point plate nor grounded, dist not grounded, points are oxidized and not making contact. sand lightly with sandpaper or nail file and retest.
needle stays to the right= points not opening,points are grounded,wire pinched in dist housing.

 

[JoeD1988]

Re: Merc 140 no spark...

needle stays to the left = points are staying open for some reason, wire to dist if bad, point plate nor grounded, dist not grounded, points are oxidized and not making contact. sand lightly with sandpaper or nail file and retest.
needle stays to the right= points not opening,points are grounded,wire pinched in dist housing.

I don't have an analog meter(guess I should get one) just a digital meter.

So now I figured out why they went with the ballast resistor. I was tracing more wiring when I found the purple wire that's supposed to run from the ignition switch through the killswitch to the left side terminal of the coil (according to Don S's awesome wiring diagram) was not hooked to anything. I began tracing that wire and checking continuity along the way to make sure there were no breaks in the wire, then I came to the main wiring harness connector and the wire didn't have continuity from the motor side of the connector to the boat side. Pulled the connector off, looked at the pins and it seems the boat side is missing the pin for the purple wire (theres not even a spot for it on the boat side connector). From what I understand that wire has a built in resistor and now that it isn't "in service" that's why they (P.O) had installed or installed the ballast resistor. It gets 12V from a wire in the main harness that only has power with the key ON, then on the bottom terminal it runs to the left side terminal on the coil. I have yet to find any kind of killswitch on this boat. I traced all of the other wires and everything seems to match up perfectly.

 

[JoeD1988]

Re: Merc 140 no spark...

Borrowed an analog meter from a neighbor and checked again, needle stays to the left. Pulled points, filed them very lightly, re-installed at a .018 gap, and tried again. Still stayed to the left and still no spark.

 

[Hoosmatroos]

Re: Merc 140 no spark...

Check for spark with an alternate method. Put a piece of carton between the points and a jumper lead on the hot side and ground (so basically short the points). Then turn on power and hold center spark lead to a big bolt on the block (not touch but almost). Remove the jumper lead for a short period and a spark jumped from center lead to the block. That way you can test it without trying to start.