1979 Mercury 115 - No Spark

[JonDick13926]

It's the 6cyl version serial number starts 54.......

When I bout the boat the guy said it didn't start because it needed a stator. I bought and replaced the stater (and also had to replace the starter solenoid). Everything works as far as the engine turning over and there being compression, but there's not spark at any of the plugs. The stator is hooked up correctly according to the instructions and the wiring harness so it's not that.

I'm wondering if the stator was never bad and that it was actually something else. But I'm not sure where to start.

I've googled it and something I read everywhere was to check the kill switch but I don't know where that is. I do have an idea though. When I installed the new stator it had three orange wires (two short and one long). The instructions said that they go to the switch boxes and to something they refered to as a switch. The instructions said that the switchbox might say that they're supposed to be black/yellow, but they're orange on the stator. I hooked the two short ones up to the switchboxes and and long orange one up to the "switch", still not knowing what that is. Do you guys think that's the kill switch?

I included a diagram.

 

[achris]

Re: 1979 Mercury 115 - No Spark

That's where I would start. Remove the kill wires from both switchboxes and see if you have spark... And on the earlier engines, yes the kill wire was orange...

 

[edwardz71]

Re: 1979 Mercury 115 - No Spark

I have the same engine 1978, My kill switch wire is orange. My problem was very random no fire cut the orange wire, been running fine since. I believe it is my toggle switch that is bad. Im gonna replace it this winter.
I don't recommend running without a kill switch though, anything can happen.

 

[JonDick13926]

Re: 1979 Mercury 115 - No Spark

Okay so first I removed the two orange wires to the switchbox and tried to restart. Still no start so I checked for spark and there was none.

Next I removed the ground from the switch that the third orange wire goes to (just to try it) and again no spark.

Yesterday I had someone help me. I cranked while he checked for spark. According to him there was no spark except one little tiny spark one time on plug #2 and then nothing. It didn't happen again. What should I try next?

 

[achris]

Re: 1979 Mercury 115 - No Spark

The next item I would check, and this is unlikely, but worth checking anyway. There is a very short white/black wire joining the 2 switchboxes together. Remove that wire and try again. (I would be spark checking with the spark plugs removed and a well charged battery).

I would also check you have the boxes connected very solidly (electrically) to the engine ground.

If you still don't have spark, then from now on you need a special meter to read voltages. It's called a DVA (Direct Voltage Adaptor).... You need to measure the voltage, with the DVA, that is being produced by the low speed windings of the stator. They would be the blue and blue/white wires coming down from under the flywheel to the switch boxes. Measure each of these voltages to ground.

Chris.........

 

[JonDick13926]

Re: 1979 Mercury 115 - No Spark

The next item I would check, and this is unlikely, but worth checking anyway. There is a very short white/black wire joining the 2 switchboxes together. Remove that wire and try again. (I would be spark checking with the spark plugs removed and a well charged battery).

I would also check you have the boxes connected very solidly (electrically) to the engine ground.

If you still don't have spark, then from now on you need a special meter to read voltages. It's called a DVA (Direct Voltage Adaptor).... You need to measure the voltage, with the DVA, that is being produced by the low speed windings of the stator. They would be the blue and blue/white wires coming down from under the flywheel to the switch boxes. Measure each of these voltages to ground.

Chris.........

Okay, I will have time to try these today. As for the DVA, I'm not sure what that is, but I have this:

Fluke 115 Digital Multimeter: The solution for field service technicians

Will this work?

 

[JonDick13926]

Re: 1979 Mercury 115 - No Spark

Okay, I did all three.

First I checked the switchbox grounds. They were good, and I sanded the contact points to make sure they stayed that way. I tested for spark and got none; I tested for start and got none.

Second I disconnected the white/black wire. No spark, no start. I reconnected it.

Then I tested the voltage (AC right?) at the blue/white and the blue wires. The blue/white was anywhere between 50-60 volts when cranking. The blue was anywhere between 50-55 volts when cranking. What is is supposed to be?

Oh, and if it matters there's 0.6 volts on the orange wires when the key is in the "on" position and approx 30 volts when the engine cranks.

 

[achris]

Re: 1979 Mercury 115 - No Spark

DVA, Direct Voltage Adaptor... Your standard Fluke meter (as nice as it is) won't work for most of these tests.... There was a thread kicking around a few years ago on how to make a simple 'plug-in' DVA Adaptor.. (No, that's not a tautology)...

Some of the signals you'll be measuring are of a very short duration (low duty cycle) and an RMS meter will not catch them....

Chris...

Here's that DVA thread. Worth reading down, some of the guys are VERY knowledgeable and there is a lot of really good information...

http://forums.iboats.com/mercury-ma...e-dva-adapter-standard-multimeter-374544.html

EDIT: Just had a look at your meter. If it has a 'Peak hold' and can catch non-sine waves, it may work

 

[JonDick13926]

Re: 1979 Mercury 115 - No Spark

DVA, Direct Voltage Adaptor... Your standard Fluke meter (as nice as it is) won't work for most of these tests.... There was a thread kicking around a few years ago on how to make a simple 'plug-in' DVA Adaptor.. (No, that's not a tautology)...

Some of the signals you'll be measuring are of a very short duration (low duty cycle) and an RMS meter will not catch them....

Chris...

Here's that DVA thread. Worth reading down, some of the guys are VERY knowledgeable and there is a lot of really good information...

http://forums.iboats.com/mercury-ma...e-dva-adapter-standard-multimeter-374544.html

EDIT: Just had a look at your meter. If it has a 'Peak hold' and can catch non-sine waves, it may work

Ahhh, I understand now. Well, my meter does have a "hold" button on it. Let me try it and I'll be back.

Btw, what voltage am I actually looking for?

 

[achris]

Re: 1979 Mercury 115 - No Spark

On the blue and Blue/wht, I'd like to see up around 200 to 300 volts at cranking speed, but the trigger wires only have a very short duration 2-5 volt signal...

 

[JonDick13926]

Re: 1979 Mercury 115 - No Spark

On the blue and Blue/wht, I'd like to see up around 200 to 300 volts at cranking speed, but the trigger wires only have a very short duration 2-5 volt signal...

I guess my multimeter isn't catching the voltage (assuming that such a voltage exists in my case). I'll now look into making the homemade dva and retrying the test asap (which isn't very fast considering I'm always on campus). But hopefully next weekend.

In the meantime, let's assume I do the test with a dva and measure something acceptable (like 200 volts). How would I proceed?

Btw, thanks for the help. I appreciate it. I'd still be scratching my head if it wasn't for this forum. I've never worked on an outboard before, and although I am studying engineering, I'm only a sophomore and haven't taken any circuits courses OR the E&M physics course so I'm still new to electricity.

 

[achris]

Re: 1979 Mercury 115 - No Spark

The trigger voltages need to be measured point-to-point, not to ground.

Here's a block diagram of how the system works... (For the Stator, HS=High Speed, LS=Low Speed)...

 

[Corrupt]

Re: 1979 Mercury 115 - No Spark

Just did some testing on my friends boat with an analog meter (needle type), and was able to figure out that we had voltage going into the switchbox from the triggers, but not coming out of it going to the coil packs. His was an '83 Merc 3cyl. and I'm not sure if yours will be the same way but the input going to the switchbox from the triggers was AC voltage. The output going to the coils should also be AC voltage. If you have power going into the switchbox on all 3 legs (the wires that lead back up and under the flywheel), but no power going out to even one of the coils then the switchbox is bad. If no power on any one of the legs coming from the triggers, then your triggers may be bad. Try the tests on your triggers and switchbox first. If your not getting any power to any of these then you may need to go ahead and make yourself a DVA adapter and test your stator and all voltages.

You will need to have another person helping you try to crank the motor while doing all this testing.

 

[achris]

Re: 1979 Mercury 115 - No Spark

Just did some testing on my friends boat with an analog meter (needle type), and was able to figure out that we had voltage going into the switchbox from the triggers, but not coming out of it going to the coil packs. His was an '83 Merc 3cyl. and I'm not sure if yours will be the same way but the input going to the switchbox from the triggers was AC voltage. The output going to the coils should also be AC voltage. If you have power going into the switchbox on all 3 legs (the wires that lead back up and under the flywheel), but no power going out to even one of the coils then the switchbox is bad. If no power on any one of the legs coming from the triggers, then your triggers may be bad. Try the tests on your triggers and switchbox first. If your not getting any power to any of these then you may need to go ahead and make yourself a DVA adapter and test your stator and all voltages.

You will need to have another person helping you try to crank the motor while doing all this testing.

While the 2 engines use the same switchbox(es) the trigger wiring is quite different (see the diagram I posted above). An analogue meter will sort of work for the stator and switchbox to coil outputs because of the inertia of the needle, but not for the trigger voltages (duty cycle too low to get the needle to move much), and a digit meter does stand a chance ...

Chris......

 

[Corrupt]

Re: 1979 Mercury 115 - No Spark

The analog meter should still work then for both sides of the switchbox. If there is any type of movement on the switchbox leg from the triggers, then for the time being assume there is voltage there. I have a feeling your going to come across one or more of those legs that doesn't have any type of swing on an analog meter which would mean no voltage either coming from the triggers or going to the coils.

 

[achris]

Re: 1979 Mercury 115 - No Spark

No spark on ANY cylinders is usually not a trigger. A faulty trigger usually stops spark on one cylinder of each pack (see the diagram for why).... The usual cause of no sparks on either pack is either a stator (bad ground), the kill wire dragging both switchboxes down, or both the switchboxes themselves (usually killed by one box being faulty in the first place)....

Chris......

 

[CharlieB]

Re: 1979 Mercury 115 - No Spark

Cranking speed MUST BE 300 MINIMUM, or the stator cannot generate sufficient voltage.

Clean all cable connections, possibly may need to clean and lube starter.

Stator has three sets of coils, low speed ign, high speed ign, and battery charging. If there is a problem with the rectifier, in some cases it can have a negative effect on speed windings. Usually this only affects high speed running. Disconnect the yellow stator to rectifier wires and retest for spark.

 

[JonDick13926]

Re: 1979 Mercury 115 - No Spark

Here's an update:

I now have a strong spark after disconnecting the orange wire running to the mercury switch. I had previously disconnected the two orange wires going to the switchbox and got nothing, but disconnecting the one going to the mercury switch gave a strong and consistent spark. Now I just need to adjust timing, and I'm selling the outboard. I need 10hp or less for a restricted lake.

 

[CharlieB]

Re: 1979 Mercury 115 - No Spark

So it appears the tilt switch was the problem, with that disconnected the ignition works correctly.

Glad you got it sorted out. Sometimes it can be a pain.

You might want to put the motor away for a short while, there are other lakes and there ain't nothin like the ole stacked 6, now that you have her going you get her dialed in and she will treat you well for a goodly number of years.