Wasted spark

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mk e
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Re: Wasted spark

Post by mk e »

NORSK wrote: Mon Mar 19, 2018 3:30 pm
mk e wrote: Mon Mar 19, 2018 3:18 pm No cam sensor....how are you fueling it? SemSemi-sequentail?

I've never had any problem with waste spark other than running out of coil dwell time, but I have had a lot of trouble with semi-sequentail injection. All the errors eith glow variation and dead-time/offest are basically doubled and can be quite large at idle/low power with big injectors.
60-2 crank trigger,fire injectors in pairs,it's called bank to bank or paired
Dwell time is no problem with "coil on plugs" i believe,even when running wasted
Normally paired is Semi-sequentail, bank is a version of multipoint, both pretty much suck at low power with big injectors. A couple times o tuned engines both ways and the was a very noticeable change....I've not bother with non-sequentail options since.

Coil on plug coils tend to need much longer dwell than distributor coils and can be a time problem in waste spark. I have LS coils on my car setup with waste spark.....I have to run slighly shortened dwell up near redline. But lower redline or maybe different coils and it would not be a problem.....but it is something you need to keep an eye on.
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Re: Wasted spark

Post by Walter R. Malik »

Walter R. Malik wrote: Sun Mar 18, 2018 9:00 pm
NORSK wrote: Sun Mar 18, 2018 5:20 pm I am working on a 4cyl 16 valve normally aspirated fuel injected engine here that for simplicitys sake it would be easy to run wasted spark
Would there be a problem with "preignition" during overlap?
This type of engine will usually see around 6deg at idle up to 26deg timing at 8200rpm
Intake has 1mm lift allready at 22deg btdc according to the cam sheet
I have also heard that the cylinder that fire during exhaust stroke uses more energy than the other one
Should not be a problem ... several modern automotive engines today use that type ignition.
I have seen great results running the Ford 4 cyl., fuel injected, 2.3L coil packs which do use "Maverick spark".

Lots of 4 cyl. motorcycles, even with simple Kettering point ignitions, use it and rev to over 10,000 RPM.
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Re: Wasted spark

Post by Kevin Johnson »

https://www.google.com/search?rlz=1C1CH ... wMYZLmK_ao

Do a search with quotation marks around the search parameters: "wasted spark" and "backfire".
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Re: Wasted spark

Post by user-23911 »

It doesn't happen.
Maybe one of those spanners that marketers throw into the works to try to sell COP.


Maybe you should ask why it is that the exiting exhaust gas doesn't set fire to the incoming charge due to it's temperature?
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Re: Wasted spark

Post by MadBill »

Yeah, especially in a two-stroke... :-k
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Re: Wasted spark

Post by user-23911 »

It's because you also need compression to set it on fire.
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Re: Wasted spark

Post by groberts101 »

joe 90 wrote: Mon Mar 19, 2018 10:50 pm It's because you also need compression to set it on fire.
Lol.. you need more than the typical hot end gasses and compression. How hot is an ignition point, oh say.. on a spark plug.. compared to the hot end gasses. Same goes for an overheated plug or sharp edge acting as a glow plug.

Ever toss a lit match at gasoline only to have the wind blow it out right before it hits the liquid? Does the still red hot sulphur ignite it?
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Re: Wasted spark

Post by Circlotron »

Buick 3.8 litre V6 motors were widely used on Australian Holden Commodores from 88 till approx late 90s. They had a wasted spark setup and were famous for backfiring when running on propane. All it needed was for a cyl to misfire once, then as the piston was getting close to the top of the exhaust stroke the wasted spark would fire but this time with lots of unburned fuel and air present. Catches alight of course, then a moment later the inlet valve opens and exposes the inlet manifold full of propane and air to a party going on in the combustion chamber.
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Re: Wasted spark

Post by MadBill »

And since gaseous fuels are usually introduced upstream of a typically large volume plenum, you get a much bigger bang... #-o

BTW compression aids mixture ignition but is not essential. When the Cadillac Northstar engine was first introduced it suffered occasional manifold-shattering backfires in that plastic component during very low temperature cold starts. The cause was found to be multi-elemental. First, in their eagerness to ensure a 'world-class' minimum crank time, the calibration engineers cut things too close on the engine rotation required to robustly snych-up the spark to the crank. The resulting mis-timed first sparks could randomly occur with open intake valves and since the engine was fitted with an additional extreme low temperature start ninth injector in the plenum, under the right (or wrong if you prefer) conditions it would fill some portion of the cylinder plus the ~ 5 liter plenum with a carefully-calibrated and atomized mixture and then the firing of one or more plugs with open intake valves would do the rest.

The fix was a longer crank time delay until first spark and JIC, adding a blow-off panel to the manifold.
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Re: Wasted spark

Post by cjperformance »

Circlotron wrote: Mon Mar 19, 2018 11:40 pm Buick 3.8 litre V6 motors were widely used on Australian Holden Commodores from 88 till approx late 90s. They had a wasted spark setup and were famous for backfiring when running on propane. All it needed was for a cyl to misfire once, then as the piston was getting close to the top of the exhaust stroke the wasted spark would fire but this time with lots of unburned fuel and air present. Catches alight of course, then a moment later the inlet valve opens and exposes the inlet manifold full of propane and air to a party going on in the combustion chamber.
Just like the coil pack fired Falcon 6's EF , AU etc, same problem on gaseous fuel. Ford upgraded the connecting rods in the factory gas engines to avoid bent connecting rods due to this.
Yes bill, the intake backfire with around 5Liters plenum and runner area full of a nice air & vapour mixture is a beauty. These push the intake valves open and pump up the hydro lash adjusters, pop out intake gaskets, split rubber intake tubing flex joints, bend throttle bodys, dislodge the LPGas mixer, busrt the air box, kill MAP sensors and air filters!
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Re: Wasted spark

Post by user-23911 »

That's all an alternative fuel problem rather than a wasted spark problem.

We had the same problem here in the mid 80s with work vans converted to dual fuel CNG fired with a distributor.
CNG requires a different initial advance and a different total advance from LPG which is different from petrol.

They backfired regularly on startup even with a distributor. They'd blow the clips off that hold on the air filter.
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Re: Wasted spark

Post by cjperformance »

joe 90 wrote: Tue Mar 20, 2018 2:38 am That's all an alternative fuel problem rather than a wasted spark problem.

We had the same problem here in the mid 80s with work vans converted to dual fuel CNG fired with a distributor.
CNG requires a different initial advance and a different total advance from LPG which is different from petrol.

They backfired regularly on startup even with a distributor. They'd blow the clips off that hold on the air filter.

Yes totally agree this is a fuel problem.
In the case of both of these two mentioned vehicles simply fittings headers with a longer path between exhaust ports is enough to alleviate the problem.
In the case of Crossfire in distributor cap slightly less plug gap helps to reduce Crossfire
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Re: Wasted spark

Post by digger »

personally i wouldn't bother with wasted spark i would do something better
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Re: Wasted spark

Post by mk e »

digger wrote: Tue Mar 20, 2018 4:19 am personally i wouldn't bother with wasted spark i would do something better
Unless you're out of ecu output channels. That is how I've always ended up with waste spark setups. It works fine as long as you check the dwell time on the coils you're planning to use.

....and the power. Waste spark uses double the power, I never really thought about that be my v12 project that needs 2 20A circuits to feed the coils instead of 1 because twice as many are firing. The car is old and has an 85A alternator...40A to coils, 30A to injectors, 20A to the fuel pump, 15A to the throttle, .....hmmmm.....no full power driving at night or with the radio on I guess unless I upgrade the alternator :shock:
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Re: Wasted spark

Post by Circlotron »

mk e wrote: Tue Mar 20, 2018 7:06 am .....and the power. Waste spark uses double the power, I never really thought about that be my v12 project that needs 2 20A circuits to feed the coils instead of 1 because twice as many are firing.
Half as many coils, each firing twice as often.
What’s this twice the power bizzo?
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