• Lab/Ignition Scope:The MODIS system has the most powerful 4-channel lab scope available. Our scope helps you radically reduce the diagnostic time associated with intermittent problems by displaying four component signatures and their interaction, simultaneously - the key to finding the root cause of intermittent problems.
• How long the primary coil is turned ON is called Dwell. Once the maximum current is reached, the coil will be at it's maximum power potential (strongest magnetic field). This is called coil saturation. Short Dwell times will not give enough time for the coil to become saturated and a weak spark will result.
• Using an oscilloscope to look at the voltage pattern as well as the current ramp of the primary side of a ignition coil. 2012 Ford Mustang 5.0 V8 COP.

There is lots more information on setting dwell here: Setting Dwell. Another Example: LS2 Coils. The LS2 coil-near-plug coils are similar in form and function to the LS1 coils described above. This 'family' of coils includes: the LS2 coil (GM# 12573190, AC Delco D514-A) from the 2005-2006 Corvette (& GTO and Avalanche),. A better, safer way is to attach a spark plug simulator to the coil secondary lead or to an individual plug lead. Just clamp the simulator to a good ground and attach the coil wire or plug lead to its terminal. If you’re troubleshooting DIS, install the simulator on one or more coils to check for spark to several cylinders.

Just what is 'Dwell' when referring to theignition system in an internal combustion engine and why does it matter? Dwellis traditionally referred to as an angle but for this explanation, Dwell can bedefined as the time during an ignition 'cycle' that current isflowing into the ignition coil. The images on the left and right areOscilloscope traces I made of what is going on electrically in a 3.8 Ohmignition coil during the interval between the generation of sparks when runningat 1440 RPM. If you assume that the graphs are representative of a 4 cylinderengine, then the 90 degrees of rotation of the distributor shaft represents theactivity within the coil for one cylinder to receive its spark. On the'blue' current curve of each image, the arrow to the left and thusthe point where the curve starts to go up, is the point at which current isallowed to flow into the primary windings of the coil. This is the beginning ofthe Dwell period. Current continues to flow as you progress to the right untilyou come to the next arrow. At this point current is abruptly stopped and theDwell period ends. Here the coil windings are fully 'saturated' andthe abrupt termination of the flow of current causes the generation of a veryhigh voltage discharge from the secondary winding which is the'spark' that goes to a sparkplug. As you progress further to theright, the voltages in the coil windings decay to a steady state until suchtime as the next 'cycle' starts when current is allowed to flow intothe coil again. By comparing the current curve in the two images, you canreadily see that there is a significant difference in the Dwell period that iscontrolled by the two different electronic control modules. As far as Dwellangle, the XR700 is about 67° and the XR3000 is about 26° at 1440RPM.

In a basic points type ignition system, the Dwell isdetermined by the gap between the contacts on the points. Once the gap isestablished, the dwell is fixed and does not change (except for wear of thecomponents). Essentially this fixed Dwell concept is found in most of theelectronic ignition units such as the Pertronix Ignitor and Crane/FAST XR700units. In the original design of all of these units, the guiding principle ofoperation was that the Dwell period must be sufficiently long such that fullsaturation of the coil will occur at the design maximum RPM. Since the Dwell isfixed, more current than is necessary flows into the coil at all lower RPM andthus adds to the heat generated within the coil. This is especially problematicfor the Atomic 4 engine due to the fact that it is a 4 cylinder engine and alsohas a low operating RPM range. These have been major factors contributing tothe coil heating and many failures that have been experienced over theyears.

Dwell Lab Scope Coil Kit

The images above are actual Oscilloscope traces made usingthe same coil, trigger mechanism, and voltage source but with anXR700module and anXR3000 module respectively. The XR3000 electronic ignition modulehas a unique Dwell Management feature that adjusts the Dwell as a function ofspeed whereas the XR700 has a very long and fixed Dwell. With the ability toadjust Dwell, the Dwell angle actually becomes Dwell Time. Consider this, for afixed Dwell angle the time that current flows gets shorter the higher the RPM.Ideally with Dwell Management you would like to have the Dwell time constantfrom idle to maximum RPM and thus assure that the coil just gets fullysaturated over the entire RPM range. The XR3000 comes pretty close todoing exactly that and thus prevents essentially all coils from overheatingwith NO BALLAST RESISTOR needed while still providing an excellentspark. Note: The Dwell is NOT user adjustable. Dwell is varied by themicroprocessor ONLY.

Dwell Lab Scope Coil Mounts

Another remarkable feature of the new XR3000electronic ignition module is a function known as 'Current Limiting'.This is an especially useful feature in that it allows the use of a very lowprimary resistance high performance coil (.4 - .5 Ohms) which can saturatequickly and always produce an excellent spark. The 'Current Limit'feature mainly comes into play in the lower RPM ranges where there is plenty oftime for coil saturation even with a reduced dwell angel. A more relevant sidebenefit of 'Current Limiting' is the feature that the module willcompletely shut off current to the coil in the event that the ignition switchis on yet the engine is NOT running! No more burned up coils and/or modules dueto a simple oversight when doing maintenance.