New Stator...no spark on #5 and #6???

[Wilky88]

I've got a 1977 Thompson with a 1982 mercury inline 6 115 HP...S/N 6007000. It was running good at the beginning of the summer but a few weeks ago I went to take it out but it wouldn't plane out, you can drop the hammer on it and it will just hit at wall at low RPMs (cannot provide an exact number as my tach isn't wired up). I replaced the spark plugs, this made no difference. After reading this forum, I decided that it must be a failed stator so I replaced that the other day and checked the spark on all plugs to find that bottom two plugs have no spark. I'm really hoping I don't have to buy a new switch box, or two for that matter! I'd really appreciate any help and/or suggestions! Thanks a lot!

 

[Ware5150]

Re: New Stator...no spark on #5 and #6???

I have the exact problem on mine. I did some troubleshooting and think I have a bad Trigger Assembly.

If you have a service manual it will tell you how to use an ohm meter and check the stator and trigger assembly. Here are the images from my manual that I used. There are 3 trigger points to measure. I had 1.3k ohms on the two that went to 1 - 4 plugs which were firing. And, 1.5Meg ohms on the ones going to # 5 & 6 which were getting no fire. Also you can switch the trigger inputs from the switch and see if you get fire on those plugs. This will tell you if your coils are good (Most likely fine).
*** Have the fuel and plugs lose if you do this. You do not want your motor to fire in the wrong sequence. ***

Hope this helps.

 

[Wilky88]

Re: New Stator...no spark on #5 and #6???

Thanks for the response! I don't actually have a manual so I'm not sure how to test the trigger...if someone could tell me how to do that it would be great!
Also...the section from your manual that you posted about the trigger...does that say each reading should be between 1100 and 1400 ohms, (1.1k and 1.4k)?? Thanks for the help!

 

[j_martin]

Re: New Stator...no spark on #5 and #6???

1 and 2, 3 and 4, and 5 and 6 are opposite each other in timing, and each pair shares a trigger coil. Check the resistance between 1 and 2 (disconnect one end), and compare it to 5 and 6. Should be near the same. I think 1400 ohms, but don't hold me to that.

Could be the coil itself, or one of the ends on the wires. (bad crimp) Either end will affect both cylinders.

hope it helps
John

 

[Wilky88]

Re: New Stator...no spark on #5 and #6???

So are you saying to disconnect one of those pairs of trigger wires from the switch box and test the the resistance between that and the corresponding trigger wire?

 

[Ware5150]

Re: New Stator...no spark on #5 and #6???

No, since the other end leads to the plug which is open you will read across the coil in the trigger. Just set your meter to Ohms and touch the leads that I have labeled. According to the manual you should read somewhere around 1.4k (1400) ohms. It says if you get anything other than this you need to replace the trigger assembly. They are labeled as touching 1 - 1, 2 - 2, & 3 - 3. I also have included the complete ign. diagram but Im not sure if you can read it.

The trigger assembly is around 131.00 and you can get it on Iboats.

 

[Wilky88]

Re: New Stator...no spark on #5 and #6???

Ware, thanks a lot for your help. I'm going to get those ohm readings in the next few days and will let you know how it goes! Thanks again!

 

[Wilky88]

Re: New Stator...no spark on #5 and #6???

Alright, so I went and checked my trigger last night. The three circuits show 1.3k ohms, right about where they should be. So I think we can eliminate the trigger. Next, I checked the coil packs for the bottom two cylinders, those seem to be working fine, they both had spark when jumped from another coil. At that point I didn't know what else to do so I checked some voltages at different places...battery reads 12.7 volts, the same at the rectifier and starter solenoid. But when I checked for voltage at the switch box, there was no voltage. There was no voltage on the red wire with the key off, and no voltage at the white wire with the key on...hoping someone can decipher all this information and give me a suggestion. I will attach a pic to show exactly where I'm reading zero volts. Thanks for your help!

 

[j_martin]

Re: New Stator...no spark on #5 and #6???

Alright, so I went and checked my trigger last night. The three circuits show 1.3k ohms, right about where they should be. So I think we can eliminate the trigger. Next, I checked the coil packs for the bottom two cylinders, those seem to be working fine, they both had spark when jumped from another coil. At that point I didn't know what else to do so I checked some voltages at different places...battery reads 12.7 volts, the same at the rectifier and starter solenoid. But when I checked for voltage at the switch box, there was no voltage. There was no voltage on the red wire with the key off, and no voltage at the white wire with the key on...hoping someone can decipher all this information and give me a suggestion. I will attach a pic to show exactly where I'm reading zero volts. Thanks for your help!

The red wire is a stator charge coil. The white wire is the bias circuit.

There is no battery voltage in the ignition circuit. You have to check the charge coil connections with a DVA at cranking speed.

With the same DVA you can check the trigger voltage. It is possible for a single turn short in a trigger coil to kill the signal to 2 cylinders and ohm out normal.

Just for grins and giggles, disconnect the bias wire between the boxes. Disconnect any other wires (advance module, etc) connected to those terminals. If one cylinder picks up, the other box is bad.

If all this checks out normal, you are the lucky owner of 2 bad switchboxes.

There is nothing better than systematic diagnostics for cost containment.

good onya
John

 

[Wilky88]

Re: New Stator...no spark on #5 and #6???

Any idea where I can get a cheap DVA?

Also, what should the cranking speed-voltages be for the stator charge coil and the trigger coils?

J Martin...thanks for your help.

 

[Ware5150]

Re: New Stator...no spark on #5 and #6???

Well you have gotten into an area that I have not been. I wish I could be more help and also am curious about this DVA. Is this a Digital Volt Amps?

 

[Wilky88]

Re: New Stator...no spark on #5 and #6???

DVA is a Direct Voltage Adapter, it plugs into your multimeter and displays peak voltage rather than RMS (average) voltage. They're kind of expensive for what they are, but you can make your own for pretty cheap.

I'm going to remove the bias wire between the switch boxes and get back to everyone with the results...thanks.