Are there any wasted spark ignition gurus out there?
Discussion
I am running wasted spark coil packs on my TVR 400SE (Rover V8 engine) which I've just finished installing. The engine runs ok and idles nicely. I believe that the odd cylinders are on the reverse polarity side of each coil pack and the even cylinders are on the normal side. If I put a timing light on the even cylinders I get a good spark at a fast rate with the arrow on the induction pickup pointing at the plug. If I reverse the pickup, the light doesn't fire, which is what I would expect.
But, if I put the timing light on any of the odd cylinders, I get the light flashing at what looks like half the speed of the even cylinders and I get the same if I reverse the pickup direction. I would have expected the pickup to only work in the reverse direction because of the reverse polarity on that plug and at the same rate as the even cylinders. Can anyone tell me if this is normal or have I got something wrong?
But, if I put the timing light on any of the odd cylinders, I get the light flashing at what looks like half the speed of the even cylinders and I get the same if I reverse the pickup direction. I would have expected the pickup to only work in the reverse direction because of the reverse polarity on that plug and at the same rate as the even cylinders. Can anyone tell me if this is normal or have I got something wrong?
What are you trying to achieve with the timing light by placing it on all leads ?
The light should flash if there is an ignition event. Simple as that really.
Some lights are better than others. Given that it is wasted spark, you will see twice as many sparks as you would normally have if it were one spark per cycle, and any rpm reading will also read double on the light.
And as such, if it's a dial back light and you use it to check timing with that method, the light will also read double.
All the wasted spark systems I've used essentially form a single circuit through one plug, its HT lead, the coil, the other HT lead and the other plug.
I think this is probably universal. If this is working correctly you should get 'equal and opposite' current through both HT leads. I'm used to strobe lights that sense on current. These should behave the same on both HT leads. If your strobe is sensitive to polarity then the pickup might need to be the right way round on each HT lead to sense correctly. To get the same reading on both HT leads the pickup side facing the coil on one lead should be facing away from it on the other lead.
With this setup, the only way you can get different behaviour on the two HT leads sharing the same coil is if there is a short to ground on one side. It's entirely possible to have this and have the cylinder on the affacted side still fire, so perhaps this is what you're seeing.
I think this is probably universal. If this is working correctly you should get 'equal and opposite' current through both HT leads. I'm used to strobe lights that sense on current. These should behave the same on both HT leads. If your strobe is sensitive to polarity then the pickup might need to be the right way round on each HT lead to sense correctly. To get the same reading on both HT leads the pickup side facing the coil on one lead should be facing away from it on the other lead.
With this setup, the only way you can get different behaviour on the two HT leads sharing the same coil is if there is a short to ground on one side. It's entirely possible to have this and have the cylinder on the affacted side still fire, so perhaps this is what you're seeing.
GreenV8S. Thanks for the response. My system is set up as you explained. The even cylinders behave as I would expect, but the odd cylinders all give this odd behaviour. I suspect you are right and I have a short to ground somewhere. I knew there was something wrong with the way it was behaving but didn't know what I was looking for. I'll try checking for a short to ground somewhere.
Polly Grigora said:
Fuel to air ratio could be causing this
HT Voltage always will find its easiest path
Engine should be running rough
I don't follow your reasoning there.HT Voltage always will find its easiest path
Engine should be running rough
How easily both plugs strike a spark will determine the shape of the discharge pulse but it will be the same for both leads, unless there's a leak to ground somewhere in the HT circuit.
fatjon said:
My Cerbera with Megasquirt pro and wasted spark coils does EXACTLY this timing light weirdness on the “other” end of each wasted spark coil but runs perfectly. Never got to the bottom of it. I put it diwn to my cheapo timing light.
Did you try reversing the polarity of the pick-up?Solved: For those who might be interested, the problem turned out to be the coil packs. They were both brand new and I bought them from a reputable stockist. The brand was Intermotor. I know some people say they are rubbish but most people seem to rate them as good quality. However, as I was at a loss as to what my problem could be, I bought new Bosch coil packs from a TVR dealer (at three times the cost of the Intermotor!) thinking that they should be using a reputable supply for parts and that has fixed the problem. The timing light now works as it should on all the ignition leads.
GreenV8S said:
fatjon said:
My Cerbera with Megasquirt pro and wasted spark coils does EXACTLY this timing light weirdness on the “other” end of each wasted spark coil but runs perfectly. Never got to the bottom of it. I put it diwn to my cheapo timing light.
Did you try reversing the polarity of the pick-up?
and I wouldnt trust an Intermotor product to break a window with 
they have always been crap since I first got into the trade (mid 80's) ign modules etc complete s
te short lived an under statment 
at times dead out of the box, at best I may use a set of ign points if I was desperate 
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