Waste spark system??????

[art leong]

I'm trying to fix a problem I have.
I'm running a 4 cylinder with a waste spark ignition system.
When I put the timing light on number 1 it is eratic and seems to be 10 to 15 degrees retarded compared to number 4.
As far as I know number one and number 4 are supposed to fire at the same time.
Anyone have an idea as to what could cause the retard in number 1?

[sst1988]

Using the right techniques and test gear should enable you to troubleshoot DIS systems with the best of 'em. Here's the lowdown.

Direct, or distributorless, ignition systems are no longer brandnew, cutting-edge technology. As a matter of fact, they've become the "conventional" ignitions of the 1990s. The first systems appeared on the Buick 3.8-liter V6 in 1983. Today, DIS is mainstream technology, appearing on most new models introduced in the past decade.

Direct (distributorless) ignition systems can be classified as being one of two types-individual-coil systems, with a separate coil for each cylinder (often called "coil-on-plug" designs), or waste-spark systems, which use one coil for every two cylinders.



Although waste-spark DIS has been with us for more than 15 years, diagnostic techniques and test equipment are still in a growth stage. More and more technicians are asking for equipment that will test these systems, preferably oscilloscopes that will provide waveforms in familiar patterns. Professional technicians also are asking for more training and troubleshooting information on waste-spark DIS. You can apply the information presented here to waveform diagnosis using either a traditional ignition scope or one of the latest-generation lab scopes.

System Operation

A waste-spark system fires one coil for each pair of cylinders that are at top dead center (TDC) at the same time. These cylinder pairs are called "running mates." One cylinder is at TDC on the compression stroke, while the other is at TDC on the exhaust stroke. The spark in the cylinder at TDC on the compression stroke ignites the air/fuel mixture to produce power. The spark in the cylinder at TDC on the exhaust stroke is "wasted," hence the name "waste-spark."

Each waste-spark DIS coil is hooked in series with its two spark plugs,. As the coil fires, secondary current creates a high-voltage spark across the gaps of both plugs. One plug fires with the traditional forward polarity of an ignition system: negative (-) to positive (+) The other plug fires with opposite polarity: positive (+) to negative (-) Thus, one plug always fires with what has always been called "reversed polarity." The voltage capacity of a DIS coil is high enough, however, to ensure that the available voltage is always high enough to fire the plug with reversed polarity when it's on the compression stroke.

Ignition oscilloscopes have always inverted the traditional negative-topositive firing voltage to show an upward firing line, or spike. Because both plugs for a waste-spark DIS coil fire simultaneously-one negative and one positive-an ignition scope cannot display the traditional voltage patterns without an electronic adapter. Several adapters are on the market-from scope manufacturers and from independent equipment makers-which invert the negative-firing voltage waveform so your scope can display it. Most of these adapters work with either an ignition scope or a lab scope.

Every Waste-Spark Pattern Is Superimposed

Because both plugs for each coil fire simultaneously, every waste-spark DIS waveform is actually a superimposed pattern of two cylinders . The waste spark in the cylinder on the exhaust stroke fires at a slightly lower voltage than the spark in the cylinder on the compression stroke. With a scope adapter that maintains the "real-time" superimposed firing display, you may see the waste spark as a bright spot three-quarters up the firing line of a parade or superimposed pattern. (Intensity will vary from one scope to another.)

Here some variety enters into the way in which DIS scope patterns can be displayed. Some scope adapterssuch as the DIScope 105 adapter that was a MOTOR Top 20 Tools award winner in 1995-maintain the superimposed firing event and display a parade or raster pattern of half the number of engine cylinders. With this kind of adapter, you must set your scope for half the number of cylinders in the engine. You also must set the scope for two-cycle engine operation because total ignition firings with a waste-spark DIS occur twice as often as a distributor ignition for a four-cycle engine.

Many hand-held digital lab scopes split the superimposed waste-spark DIS firing event and display a waveform for each cylinder. Digital sampling technology makes it possible to select one cylinder from a superimposed pair and display its firing event separately from its running mate. In a parade or raster DIS pattern that displays all six cylinders of a V6, for example, the second half of the pattern is a repeat of the first, but the alternate cylinders are displayed. Then every cylinder is alternately displayed on the power stroke and the exhaust stroke.

It's not really complicated if you concentrate on the secondary pattern and what you've known about ignition waveforms for years. The engine is still a four-cycle gasoline engine, and the ignition system is still an inductive-discharge ignition. Moreover, your scope-old-fashioned analog ignition scope or modern digital lab scope-is still synchronized by the No. 1 cylinder pickup. Therefore, parade and raster patterns still appear in firing order sequence.

All of the pattern examples shown here are based on a scope adapter that maintains the superimposed firing event and displays a V6 parade or raster pattern as three superimposed pairs. This puts DIS troubleshooting in the context of the familiar ignition scopes we've known for decades

[sst1988]

No Spark Line, Open Spark Plug Cables. are parade and raster patterns with no spark lines. These are more examples of open-circuit conditions, which usually indicate disconnected or open plug cables.

Long, Low Spark Line, Few Coil Oscillations: Fouled Plug or Shorted Coil. are raster and parade patterns that show a long, low spark line and few oscillations for one coil. This usually indicates a badly fouled plug or plugs, or a shorted coil.

High, Short Spark Line: Lean Mixture or Wide Plug Gap. Figs. are raster and parade patterns that show a high, short spark line for one coil. This is a common sign of a lean mixture or very wide plug gap in one or both cylinders for that coil. If the problem is a lean mixture, it may be due to a vacuum leak that affects only one cylinder.
Mistakes To Avoid Jumping Spark Line. an unstable spark line for one coil. It appears to jump up and down at random. This is often caused by a sticking or worn valve in one cylinder that causes an uneven air/fuel ratio.

Upward-Sloping Spark a spark line for one coil that slopes upward as it ends. This is similar to the jumping spark line , but usually indicates sticking or floating valves if it appears at all speeds. It also can indicate burned valves, wide plug gaps or a vacuum leak that affects several cylinders.

False Trigger: Bad Crankshaft or Camshaft Sensor. is a raster pattern with a false trigger signal on the waveform for one coil. This may indicate a bad crank or cam sensor, and may appear randomly for various cylinders. Other causes may be a bad ignition module, radio frequency interference (RFI) with the ignition module, shorted sensor wiring or a dirty or bent trigger wheel for the sensor.

Check Waste-Spark on Parade

To close this report, we'll point out an extra feature of digital lab scopes that split the superimposed waste-spark DIS firing event. When a scope displays a waveform for each cylinder, you can compare the waste spark to the power spark for each cylinder. If the wastespark firing line seems higher than normal, or higher than the waste spark for the other cylinders by comparison, you're probably looking at high resistance in the portion of the circuit to that cylinder.

The problem might be an open or high-resistance plug wire or an accidental gap at the connection to the coil or the plug. Whatever the source, the high resistance can lead to a misfire. If you recognize this symptom, you're on your way to solving the problem.

[sst1988]

Most dial back timing lights will read DOUBLE the actual timing when using the dial back function on wasted spark engines. If you set the light to 0 degrees, it should read correctly though.

The reason they read double is that the timing light calculates the engine RPM from the igntion pulses and then calculates how long to delay the flash of light based off of RPM so that it takes the desired amount of timing out. What happens on a wastespark car is that since the coils are firing once per rotation instead of once every two rotations, (which is what the timing light is expecting to see) the timing light thinks the engine is spinning twice as fast as it actually is so that the delay time of flash is half as long as what it needs to be. The user then turns the knob more until the timing light lines up with zero, and the value on the timing light is then double the actual ignition timing.

Some timing lights come with wastespark adapters but if you don't have one, just make sure you take this doubling into account or have the light set to 0 degrees when checking timing.

I personally first saw this a couple years ago when I was dynoing a wasted spark engine which seemed to like to idle at 30 degrees timing, or so the timing light led me to believe, with a value of 15 degrees timing in the ECU. I then adjusted the offset in the ECU so that the timing light and ECU read the same timing at idle, like anyone would do. Then, when we began to do pulls, the engine seemed to be down on power unless I had a value of 37-40 degrees of timing in the igntion map. At this point, we knew something was not right so we mechanically checked the position of the crank and cam pickups and used a spare non-dialback light with additional marks scribed on the crank pulley. I then resynced the timing to the ECU and continued the dyno the engine. After that, everything seemed normal so we attributed it to a F'd up timing light.

Now, move forward a few months. Another engine for the same car with sightly different cam and headwork specs on the same exact dyno, with a new dialback light. Same thing happened again!! It was then and there that I had an idea of what was going on. This time I synced the timing with the dial back at double the value, 30 on the light and 15 in the ECU. I then checked it with the non-dial back light and it was spot on.

Looking back, I wish someone had told me about this as it would have saved quite a bit of head scratching and dyno time!!!



i hope this information helps.sst1988

[art leong]

Thanks
this is what was happening to me. I had a Snap-On light, which I thought was bad. I just bought a new light a Equus-Inova.
Same thing
But I still get a different reading when I hook it up from number 1 to number 4 Number 4 seems like its right number one seems to bounce around.

[Pat Cook]

Art, just for giggles, does it do the same thing when checking 2&3? could it be there is some sort of "fly back voltage" on the wasted spark cycle? caused from a weak condenser or missing condenser?