How to Safely Disable the Ignition Coil

[TomoHawk]

One suggestion by "experts" to help protect your car from being stolen is to disconnect the HT wire from the ignition coil, (or remove the rotor, mix up the spark order, etc.)  but that seems like an obvious thing for a thief to look for, except for that last one.

But what if you had some kind  a "dummy wire?"  Just disconnecting the HT wire means you will have arcing from the coil, which will harm the coil, and disconnecting only one spark plug will still allow the engine to run, albeit slightly poorly (BTDT  ) so if you had a safe way to allow the HT charge to go to ground, the engine will turn over and everything will "look" like it should, but still not start.

So what can we do to allow the coil to discharge  without going to the spark plugs, and not harming the  coil?

I'm not referring to cutting the 12V wire to the ignition coil, as that is another thing, and is more involved than just removing the HT wire, so please don't mention that here.

 

BTW- has anyone ever heard of a "G-spot?"  It's an electronic doohickey that goes into the starter solenoid wiring and requires to touch it to enable the starter  to be activated.

 

[Chickenman]

The " G-Spot " is a myth. Mystical spot meant to frustrate men over the ages...  

[Zed Head]

Arcing, or discharging to ground, from the coil won't hurt it.  You could make a T off of the center wire that runs to a switched ground.  Close the switch and coil discharge just goes directly to ground.  Open it and it passes to the distributor.

[Mikes Z car]

  I have wondered about the idea of making a plastic tubular case for the ignition coil to make it longer so that there would be a hidden compartment in the end away from the wires that could conceal an RF receiver device to disable the ignition. It could house a circuit and relay to disable the ignition.

  I told a lady friend I know about the G spot post, she claims it is real but   ...er ah um... is not available for demos.

Edited February 4, 2017 by Mikes Z car

[Captain Obvious]

Problem I see with having a way to short the high voltage side to ground is that the spark is likely to jump the switch to ground even when you don't want it to. See all that thick silicone insulation on the spark plug wires? It's there because you need all that insulation to keep the spark contained and prevent jumping to ground. I'm having a hard time coming up with anything discreet that can handle the voltage when it's supposed to be open.

I mean, I can picture a huge knife switch with contacts two inches apart, but that's not discreet. 

I think it would be better to just disable the circuit on the primary side. Is there some reason it's more desired to do the disabling on the secondary side?

[Zed Head]

With a solid path to ground through the switch, you'd end up with two possible low resistance paths, one to the distributor or one directly to ground.  So the gap would easily be jumped only if the easy path to ground wasn't there.  Right?  That's where I ended up.  The same thought did enter my mind though.  But I kicked it out

[TomoHawk]

The thing that got me to think about this is that if a thief opens your bonnet and sees a switch or something like that interrupting the q12V line to the ignition coil, then he would just jump that  and be off with your car.  But, if everything "looks" OK, and the engine still won't start, then  he might just move on.  I would suppose you could  splice into the 12V line to the coil somewhere by the brake  booster, then it could be disguised.

And the more hurdles you can put into the car to prevent someone from driving off with it the better.

If you wanted to disable the ECU, will removing one of the green fuse links to that?  Doesn't the ECU go into "limp mode" then?

BTW-    I saw something called an ignition immobilizer on Jaycar.com.  It supposedly lets the engine start and a couple seconds later kills the ignition.

[Captain Obvious]

Hmmm... Not sure I explained my concern properly. My concern isn't when the switch is in the disabling position. I believe it is easy to short the spark to ground. Even on the high side... No problem.

My concern is what happens when the switch is in the normal "non-disabling" open position. The concern is what prevents the spark from jumping across the open contacts in the switch (where you don't want it) instead of jumping the gap at the spark plug (where you do want it).

The simple answer is "distance". But distance takes size, and size makes for non-discreet. And don't think for a minute that just as long as the gap inside the switch is greater than the spark plug gap that you'll get the spark only where you want it. Not only is high voltage a little unpredictable, but the desire for the spark to jump the gap actually decreases under compression. That means you'd need something significantly larger gap at one atmosphere.

So I'm back to a big 'ol knife switch mounted on the inner fender well. Label it "RUN" and "STOP". 

[TomoHawk]

Maybe you should label it, Steal my car" and, "not worth stealing."  LOL!

 

[Zed Head]

Actually I think with good contact made the current wouldn't jump a decent-sized gap.  Look at how an over-gapped plug can cause misfires.  You have to leave some work for the doer, once you supply the idea.  There are also solid-state switches, which don't use gaps.  I know that they exist but I don't know much about them.  Or the dielectric filled type, used to be PCB's, don't know what they use now, probably silicone fluid.

Personally, I'd just find a different way.  The question is interesting to discuss though.  I had a reason to go browse around high voltage switches. http://www.behlke.com/separations/separation_b1.htm

and dielectric fluids  https://en.wikipedia.org/wiki/Liquid_dielectric

How about killing the points ground or ignition module side?  The negative side of the coil, instead of positive.  Or the trigger circuit for electronic?  No circuit breakage, no magnetic field collapsing, no spark happening.  A switch on the wires (green or red) to the module from the variable reluctor maybe.  That would work and the common thief would have no clue where to look.  Or isolate the distributor body and use a dedicated ground wire, with a switch in it, for points.  You can supply all the power you want, but if the coil current doesn't make and break, you get no spark.  Just brainstorming now...

 

 

[TomoHawk]

 

In stead of a switch, a specially made HT wire to create  " over-gapped " effect?  You just substitute that for the regular HT wire, and it all looks stock.

I hate having to open the wiring bundle, but a switch in the 12V line to the coil is starting to look like the desired choice.

[Captain Obvious]

When the coil discharges, that energy WILL go somewhere. Physics dictates that it simply MUST. The problem is that if you don't encourage that energy to go somewhere you want it to, it may go somewhere you don't.

With a hollow dummy HT wire on the coil, that energy will look for a different path, and you don't want that to happen. It could create a carbon trace on the body of the coil and arc from the coil nose to the body. It could create a corona discharge little plasma cloud at the coil nose and the ozone created could ruin all the rubber insulation in the area. It could reflect back into the primary side and damage your ignition module, condenser, or points. I'm no high voltage expert, but it just sounds like a bad idea. I've worked on a couple systems that even warn against intentional continued misfires like that because of potential damage to the ignition system from the reflections.

The title of the thread is "How to Safely Disable the Ignition Coil ", and I believe the answer is "By disabling it on the primary / low voltage side."

There are lots of ways to do that, but if it's for theft resistance, the trick is to make it easy for the owner to use while making it difficult for the thief to detect, disable, or bypass.