Ignition question..

Reply

  #1  
Old 06-29-15, 08:16 PM
Member
Thread Starter
Join Date: Jun 2015
Location: US
Posts: 5
Ignition question..

Ok so my question revolves around a garden tractor. I know it's probably fairly uncommon here but it does run on 12VDC so the principles are the same as a car or any other low voltage application.

Long story short, I have a tecumseh engine that originally ran a Solid State Ignition (SSI) that has failed. Following Ed Stoller @Circuit Diagram & Explanation instructions I wired up Option 1, then Option 2. Why? because for some reason I cannot get more than 6.5vdc at the coil + post. Going with Option two eliminated the aged key switch. So as it sits right now I have Battery to ballast resistor (1.4ohm) input, to Coil +.. Measuring at ballast input I read 12.4vdc, at coil + I read 6.5vdc.


Now quite literally the physical chain is (using brand new 14gauge wire, 120v rocker switch, ballast resistor and automotive ignition coil) battery, rocker switch, ballast input, coil +

Surely 1.4ohms is not enough to halve 12 volts right? Any suggestions on what the problem could be?
 
Sponsored Links
  #2  
Old 06-29-15, 08:21 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 46,108
Welcome to the forums.

This thread could actually be in the small engine forum but your question is really about voltage drop.

Yes.... the ballast resistor is there to drop voltage to the coil and measuring 6.5vdc on the coil is just about normal.
 
  #3  
Old 06-29-15, 08:35 PM
Member
Thread Starter
Join Date: Jun 2015
Location: US
Posts: 5
Thanks PJ.. so a typical auto coil should be able to fire off a measly 6.5 volts?
 
  #4  
Old 06-29-15, 08:42 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 46,108
Yes..... and less than that.
 
  #5  
Old 06-29-15, 08:51 PM
Member
Thread Starter
Join Date: Jun 2015
Location: US
Posts: 5
Interesting. I did realize I forgot one thing to check.. the coil itself. I get 1.6O on the primary and 8.6k on the secondary. So it seems that the coil is fine.

Let me ask you this, based off Ed's Option two, do you have any thoughts as to why I get zero spark on the plug?

I mirrored his setup, ground is good on both battery and ignition module, every bit of physical wire is brand new 14ga. Coil, resistor, ign mod, and spark plug wire are all brand new. Incidentally the spark plug wire ohms at 7.2k if that matters.
Spark plug is ground via hose clamp to a head bolt.. I get a single spark upon turning on the rocker switch. The chrysler ignition control module (CM) is getting it's required 8+vdc on terminal C.

I'm honestly dumbfounded.
 
  #6  
Old 06-29-15, 09:40 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 46,108
Why aren't you just replacing the defective ignition module ?

How are you triggering whatever ignition module you're using now ?
I don't see a ballast resistor in option 2.

Name:  option2c.jpg
Views: 621
Size:  26.5 KB
Diagram from Ed Stoller
 
  #7  
Old 06-29-15, 10:22 PM
Member
Thread Starter
Join Date: Jun 2015
Location: US
Posts: 5
The ballast resistor is needed if your coil does not have a resistor builtin. As most, more expensive coils do.

The whole reason to why someone would do this is because the original SSI modules have been EOL for quite some time. Refurbs on ebay still command a hefty $250-ish.

So you build an 'automotive battery powered' type system for a fraction of the replacement cost.

I took the dead SSI, isolated the pickup coil/magnet it has builtin, bridges it to a terminal on the external usually used for the kill wire, to ground it to stop ignition and thereby the engine. Killing an engine with this setup is handled by shutting off battery juice. Ed outlines how to DIY an SSI module on his website. I've ohms the coil and it reads within specs ( i cant recall the actual figure right now).

The possibility does exist that I have a dead dead SSI module. I realize that, but before replacing it with a $60 pickup coil I need to try to verify all the other parts are working as intended.
 
  #8  
Old 06-30-15, 06:56 AM
Rough Rooster's Avatar
Member
Join Date: Feb 2014
Location: USA
Posts: 381
Wired up one of these on a Tecumseh. Followed Ed's instructions and everything worked fine.
Do you have the correct spacing between Ed's trigger and the flywheel magnet?

Is your Chrysler module a good one?

I used an outside resistor like was used on late 50's and 60's GM products.

To test for spark: disconnect the + lead and 'scratch' it on battery terminal. This will provide many on-off cycles and you can observe if the Chrysler module is working.

RR
 
  #9  
Old 06-30-15, 10:06 PM
Member
Thread Starter
Join Date: Jun 2015
Location: US
Posts: 5
Wow very nice Rooster. Actually today I got it working. At work this morning I was thinking that the only real piece left to check was the modules ground and my pickup coil. What you dont see on Ed's website anymore (and I cant figure out why) is how to modify a dead SSI to be your pickup. You basically remove half the potting and feed the red coil wire to the kill terminal via a diode. then ground the black leg/wire. I had soldered the diode to a different section of the module.. not to the kill terminal.. Once I corrected that, set the air gap to .020 she threw sparks like the 4th of July. Well not really but she did spark.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes