Waste Spark System – how does it work?

[rt54321]

Okay,

After googling/youtubing the waste spark system, I see two different ways of describing the waste spark ignition system, where two sparks are generated, and this tells the car computer the timing (as opposed to using an actual cam sensor).

Method 1) Considering a mated cylinder pair (for instance, cylinders 1 and 4 on a 4 cylinder car), cylinder 1 is on compression stroke, while cylinder 4 is on exhaust stroke. Cylinder 4 spark plug will fire first (because it’s not under high pressure). Therefore, computer knows that cylinder 1 is on compression stroke (and thus, the timing can be deduced).

Method 2) Something about the current flow direction in the spark plug. The high voltage will flow positive to negative in the compression spark plug (let’s say cylinder 1 is on compression), then the spark current will “cross over” to cylinder 4 through the engine block, and then the spark current will flow from cylinder 4 spark plug back to the ignition coil through cylinder 4’s spark plug (the current is traveling from ground to electrode in cylinder 4 – “reverse direction”).

I’m a bit confused – can someone shed some light on DIS timing for waste spark ignition?

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[valde]

If engine doesn’t use sequential or direct fuel injection and has waste spark ECU doesn’t even need to know the cam timing. If each cylinder has its own coil then all cylinders have spark in the “correct” direction. If there is coil per 2 cylinders then another one of those cylinders has its spark in “correct” direction and another in “opposite” direction.

Is there an engine with sequential or direct fuel injection without cam sensor?

[rt54321]

Hi valde,

Here are some more details I should have included before:

It’s in reference to my 2004 Chevy Malibu 2.2L ecotec engine (I’m not sure exactly what kind of fuel injection it has).

–> After doing some more research, I realized that there is “wasted spark” ignition, and then there is “compression sensing” ignition, which is a subset of wasted spark ignition.

–> Compression sensing ignition does not use a cam position sensor.

–> There are other kinds of waste spark systems that DO use a cam position sensor (this was my mistake – I assumed that ALL waste spark systems do not have a cam sensor, which is incorrect).

[valde]

I still can’t completely understand your question. This article http://www.motor.com/magazine/pdfs/112004_11.pdf explains it very good to me but I am an expert in electronics. ECU uses both the voltage and time of spark event to determine cam phase.
When ECU commands the sparking event to start for cylinder 1 and 4 voltages in spark plug cap on both of those cylinders starts to rice. In spark plug 1 voltage of center electrode is positive and in cylinder 4 it’s negative but actually that’s irrelevant in determining the cam timing. The cylinder that’s on exhaust stroke sparks first when voltage hasn’t risen very much. The cylinder that’s on compression stroke needs bigger voltage so spark comes later. ECU then can use time difference and difference in amount of voltage to determine cam timing.

[Author]

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