Forums

Monitor Automotive Spark Plug?

Started by eeboarder May 15, 2009
What kind of electrical signal is involved with the spark plug? I know the
voltage is amplified with a induction coil to thousands of volts, but is
the signal just a simple pulse? What kind of current is there? Does the
current create the spark and then return through the same cable?

I just hooked a split core current transformer with 3000 windings around a
spark plug cable and got nothing. I'm trying to re-create a signal similar
to that which a timing light would use. 

Really, I would like to just know when this engine is on and off without
any lag. I also don't want to shutdown the engine to install it.

Any ideas or help would be much appreciated.
eeboarder wrote:
> What kind of electrical signal is involved with the spark plug? I know the > voltage is amplified with a induction coil to thousands of volts, but is > the signal just a simple pulse? What kind of current is there? Does the > current create the spark and then return through the same cable? > > I just hooked a split core current transformer with 3000 windings around a > spark plug cable and got nothing. I'm trying to re-create a signal similar > to that which a timing light would use. > > Really, I would like to just know when this engine is on and off without > any lag. I also don't want to shutdown the engine to install it. > > Any ideas or help would be much appreciated.
Google Kettering Ignition. It's a little more complicated than meets the eye.
> What kind of electrical signal is involved with the spark plug? I know the > voltage is amplified with a induction coil to thousands of volts, but is > the signal just a simple pulse? What kind of current is there? Does the > current create the spark and then return through the same cable?
You probably already suspect this but this is what I suspect, and I'm no expert: Before electronic ignition, a simple switch driven by a rotating cam triggered spark plugs. I suppose the electronic ignition systems can tailor the pulse to whatever is required. To actually capture the switching event would be next to impossible because a car is one of the most electrically dirtiest systems around.
> I just hooked a split core current transformer with 3000 windings around a > spark plug cable and got nothing. I'm trying to re-create a signal similar > to that which a timing light would use.
Lots of windings = a low pass current filter, right? Easy to miss a fast transient event. Perhaps an optocoupler with sufficient protection so the diode won't blow would be a better way to tap into the spark plug signal. Of course, it's all based on my amateur speculation. JJS
On Fri, 15 May 2009 16:11:35 -0500, eeboarder wrote:

> What kind of electrical signal is involved with the spark plug?
If it carries power it's not a signal. It's drive. It's high voltage and (relatively) low current.
> I know > the voltage is amplified with a induction coil to thousands of volts, > but is the signal just a simple pulse?
It'll be mostly a rapidly decaying pulse, yes.
> What kind of current is there?
Do you mean "how much"? Not much, but I don't know the details.
> Does the current create the spark and then return through the same > cable?
No, the return path is through the engine block.
> I just hooked a split core current transformer with 3000 windings around > a spark plug cable and got nothing. I'm trying to re-create a signal > similar to that which a timing light would use.
Then why don't you go buy a cheap clamp-on timing light and either just use it's measuring head or take the thing apart to see how it's built?
> Really, I would like to just know when this engine is on and off without > any lag. I also don't want to shutdown the engine to install it. > > Any ideas or help would be much appreciated.
I agree with Mr. Stewart: do a web search on "Kettering ignition" or just "automotive ignition" and see if you can find some numbers. Looking to see if anyone has a timing light project may be a good deal, too. -- http://www.wescottdesign.com
On Fri, 15 May 2009 18:46:36 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:

><snip> >> I just hooked a split core current transformer with 3000 windings around >> a spark plug cable and got nothing. I'm trying to re-create a signal >> similar to that which a timing light would use. > >Then why don't you go buy a cheap clamp-on timing light and either just >use it's measuring head or take the thing apart to see how it's built? ><snip>
That was my thought. I've got one here from Sun and it just clips over (around it, no galvanic connection) one of the spark plug wires. Works fine. Odd memory of it pops back -- that one was bought at Fred Meyer and I didn't want to pay the $64.99 they were asking for it, so I called over the manager of the day and negotiated. Got it for $35. The OP may need to also examine the conditioning circuit, though. Figuring it out isn't necessarily 'easy.' Jon
On Fri, 15 May 2009 18:46:36 -0500, Tim Wescott wrote:

> I agree with Mr. Stewart: do a web search on "Kettering ignition" or just > "automotive ignition" and see if you can find some numbers. Looking to > see if anyone has a timing light project may be a good deal, too.
Hmm; the first hit on Google for "DIY timing light" is this: http://www.halfbakery.com/idea/DIY2 WARNING: the above article should not be taken seriously. For some reason, most of the other hits were link farms. But I did come across one relevant article: http://www.siliconchip.com.au/cms/A_104378/article.html [Scroll down to "Automotive LED timing light".] This suggests 100 turns on a ferrite or powdered iron core (a silicon steel core designed for 50/60Hz mains probably isn't suitable for short pulses).
"Nobody" <nobody@nowhere.com> wrote in message 
news:pan.2009.05.16.04.44.49.94000@nowhere.com...
> On Fri, 15 May 2009 18:46:36 -0500, Tim Wescott wrote: > >> I agree with Mr. Stewart: do a web search on "Kettering ignition" or just >> "automotive ignition" and see if you can find some numbers. Looking to >> see if anyone has a timing light project may be a good deal, too. > > Hmm; the first hit on Google for "DIY timing light" is this: > > http://www.halfbakery.com/idea/DIY2 > > WARNING: the above article should not be taken seriously. > > For some reason, most of the other hits were link farms. But I did come > across one relevant article: > > http://www.siliconchip.com.au/cms/A_104378/article.html > > [Scroll down to "Automotive LED timing light".] > > This suggests 100 turns on a ferrite or powdered iron core (a silicon > steel core designed for 50/60Hz mains probably isn't suitable for > short pulses). >
Farnell or RS used to sell the clip on inductive pickup units at a reasonable price - at least they did 6 or 7 years ago.
In message <b7GdnT1B_esaR5DXnZ2dnUVZ_sqdnZ2d@giganews.com>, eeboarder 
<jmeyer@emittechnologies.com> writes
>is >the signal just a simple pulse?
No. It's got several distinctly different characteristics, you can tell an awful lot about the quality of the engine and ignition system with the spark signal.
>What kind of current is there? Does the >current create the spark and then return through the same cable? > >I just hooked a split core current transformer with 3000 windings >around a >spark plug cable and got nothing. I'm trying to re-create a signal >similar >to that which a timing light would use.
Then get a hold of a timing light clamp and see how it's done. Get a hold of a clamp on EMI filter, wind ~ten turns of enamelled copper wire around one half of the ferrite and then attach a scope to the ends of the ECW, see what sort of signal you get out. I guarantee it's not a 'simple' pulse.
> >Really, I would like to just know when this engine is on and off >without >any lag. I also don't want to shutdown the engine to install it.
Tap into the crank sensor, tap into the ignition coil LT drive signal or the injector drive (assuming it uses fuel injection). I had success using hall effect sensors on fuel injector bodies and also on ignition coils, extremely easy to deal with and also logic compatible if you pick the right one although a simple comparator circuit worked best as it was adjustable to suit. Plenty of ways to tell if an engine is running that are simpler to interface to and measure than a spark plug lead.
> >Any ideas or help would be much appreciated.
-- Clint Sharp
On May 16, 12:13=A0am, Clint Sharp <cl...@clintsmc.demon.co.uk> wrote:
> In message <b7GdnT1B_esaR5DXnZ2dnUVZ_sqdn...@giganews.com>, eeboarder > <jme...@emittechnologies.com> writes>is > >the signal just a simple pulse? > > No. It's got several distinctly different characteristics, you can tell > an awful lot about the quality of the engine and ignition system with > the spark signal.
Hi This used to be true when the typical coil continued to dump energy into the spark plug, long after the flame front left the plug. The capacitive discharge systems most often used today only create a short pulse that is too short to get any useful reading on the preasure changes right after the flame is ignited. With the long discharge, one had a voltage signal that was proportional to the pressure. Too fast a burn rate would indicate a lean mixture and too slow would indicate too rich. Jumps in preasure might indicate detination from buildup in the cylinder. A low line could mean low compression. But, as I said. All that information is lost in the short pulse of todays more efficient ignition systems. Dwight
> > >What kind of current is there? Does the > >current create the spark and then return through the same cable? > > >I just hooked a split core current transformer with 3000 windings > >around a > >spark plug cable and got nothing. I'm trying to re-create a signal > >similar > >to that which a timing light would use. > > Then get a hold of a timing light clamp and see how it's done. > > Get a hold of a clamp on EMI filter, wind ~ten turns of enamelled copper > wire around one half of the ferrite and then attach a scope to the ends > of the ECW, see what sort of signal you get out. I guarantee it's not a > 'simple' pulse. > > > > >Really, I would like to just know when this engine is on and off > >without > >any lag. I also don't want to shutdown the engine to install it. > > Tap into the crank sensor, tap into the ignition coil LT drive signal or > the injector drive (assuming it uses fuel injection). > > I had success using hall effect sensors on fuel injector bodies and also > on ignition coils, extremely easy to deal with and also logic compatible > if you pick the right one although a simple comparator circuit worked > best as it was adjustable to suit. > > Plenty of ways to tell if an engine is running that are simpler to > interface to and measure than a spark plug lead. > > > > >Any ideas or help would be much appreciated. > > -- > Clint Sharp
In message 
<b8f58bbd-38aa-4b54-a226-6182e0662b47@i28g2000prd.googlegroups.com>, 
"dkelvey@hotmail.com" <dkelvey@hotmail.com> writes
>Hi > This used to be true when the typical coil continued to >dump energy into the spark plug, long after the flame front >left the plug.
Mmm, entirely true although some manufacturers do measure burn efficiency after the ignition pulse by applying a high impedance, high voltage to the plug, I believe they measure by applying a high impedance high voltage to the plug, Mitsubishi and Saab spring to mind for some reason. -- Clint Sharp