Difference between Basic and Classic versions of the MisGen3 CCB
Because some users have occasionally requested that Global provide a variant of the CCB that does not contain circuity unneeded in their testing, Global has decided to make this version available for purchase by all customers at a reduced cost. This de-contented version is called a “Basic” CCB, to distinguish it from the traditional CCB, which is now called the “Classic” version. (Figure 1 shows both versions side by side.) Note that both versions are appropriate for traditional “non-ICD” ignition systems, and are not to be confused with the MisGen3 ICD boxes used on engines with Integrated Coil Driver (ICD) ignition.
Figure 1 Basic and Classic versions of the MisGen3 CCB. Note the Basic’s absence of blue banana jacks, which in the Classic version connect to circuitry that has been eliminated from the Basic version because relatively few customers need it.
The purpose of this web page is to explain the one functional difference between the Basic and Classic versions of the CCB. The brief answer, which is elaborated upon in subsequent paragraphs, is that the Classic version can be connected to the ignition primary wires in such a manner as to defeat a certain type of diagnostic employed by some production ignition controllers. This type of diagnostic can be described as a “primary coil flyback voltage” diagnostic, but it is less common than the “primary coil current diagnostic” that most ignition controllers contain in their hardware/software. Although the Basic version of the CCB defeats the diagnostic based on primary coil current, just like the Classic version, it does not contain the components needed to defeat the primary coil flyback voltage diagnostic like the Classic does.
Note: There is no difference in the method by which the two versions create misfire or are controlled from the pendant. Table 1 below summarizes the characteristics of the two boxes, with the one difference just explained highlighted in red.
Table 1 Comparison of features in Basic and Classic version of CCB
Characteristic | Basic | Classic | Comments |
---|---|---|---|
Create misfire | Yes | Yes | no difference |
Defeat primary current diagnostic | Yes | Yes | no difference |
Defeat primary flyback voltage diagnostic | No | Yes* | * only when connected to blue jacks |
In this context, “defeating” an ignition diagnostic means that MisGen3 creates misfire by preventing spark ignition in a manner that is undetectable by the diagnostics built into the production ignition controller. This characteristic is very important because the misfire generator is intended to test the functionality of the OBD misfire detection, not the on-board diagnostic for ignition failure. If the actions of the misfire generator were detected by the ignition diagnostic, not only would it set a Diagnostic Trouble Code (DTC) for the ignition system – which is not desirable in a test for the misfire DTCs – it might also invoke a Failure Mode Management strategy that turns off fuel to the detected faulty cylinder all of the time – even if the misfire was induced only part of the time on that cylinder by the MisGen3.
The reason that the lower-priced Basic version may be attractive to many customers is that their ignition systems do not contain a diagnostic that monitors the flyback voltage on the driven side of the primary coil at the moment of ignition. Thus, there is no need for such customers to pay for circuity to defeat a diagnostic that does not exist on any of their engines.
How to tell if an ignition system includes a diagnostic based on flyback voltage
Most OBD engineers are not familiar with details of their ignition system’s diagnostics. They may know that an ignition diagnostic exists, but may not know whether it detects current flow, flyback voltage, or both. Because it may be difficult to obtain reliable information on this subject, we provide a fool-proof method for determining whether or not the primary coil’s flyback voltage is monitored by the ignition diagnostic. (We don’t care whether a diagnostic for primary current exits, because both versions of CCB do not alter current into the coil driver – power transistor – and thus do not trip a diagnostic of such.)
Unfortunately, this method requires access to a MisGen3 CCB system (either Basic or Classic) to perform a brief engine test. If customers have previously used the MisGen3 system – either from their own inventory or borrowed from business partners – they may already have the answer to this question. The reason is explained below in material derived from the original instruction manual to the MisGen3.
The manual depicts two alternative ways of connecting the (Classic) CCB to the ignition. The simpler method, shown schematically in Figure 2 and visually in Figure 3, requires only a “T” connection to each harness wire that feeds an ignition coil primary. Note that the control signal is not interrupted between the ignition coil and the ignition controller (often housed in an ECM, but sometimes in another entity). The control line signal is tapped at some point in the harness and fed into a corresponding channel of the MisGen3 using the white banana jacks on the CCB. The blue banana jacks remain unconnected.
Figure 2 Schematic showing attachment of MisGen3 CCB to ignition wiring via “T” connection.
Figure 3 Attachment of MisGen3 CCB via “T” connection uses only white banana jacks.
In this configuration, the MisGen3 can create misfire and defeat a current-based diagnostic in the ignition controller; however, it will not defeat an ignition diagnostic based on flyback voltage. For that to occur, the CCB box must be connected in a “Y” configuration, depicted in Figures 4 and 5 in the next section. This configuration breaks the lines between the ignition controller and coils, by connecting the control signals to the blue jacks on the CCB while connecting the white jacks to the ignition coils.
Figure 4 Schematic showing attachment of MisGen3 CCB to ignition wiring via “Y” connection
Figure 5 Attachment of MisGen3 CCB via “Y” connection uses both white and blue banana jacks.
Note that misfire is still created the same way as done in the “T” connection – by clipping the flyback voltage that would otherwise exist on the coil primary at the moment of ignition if it were not being misfired. However, because the “Y” connection inserts a diode in the path between each channel of the ignition controller and its driven coil, an inductor (one per channel) inside the CCB box is able to generate a pseudo (fake) flyback spike of several hundred volts at the moment of ignition to fool the ignition diagnostic into thinking that the ignition event was normal, even though in reality it is misfired due to clipping of the coil’s actual flyback voltage. (See “… clipped flyback voltage” on next page)
Being simpler to connect, more users employ the “T” connection instead of the “Y” connection at first. If the production ignition diagnostic does not monitor the flyback voltage spike, then no ignition error DTC is generated, and all is well.
On the other hand, if the engine’s ignition controller does include a diagnostic that flags the absence of flyback voltage on the coil primary, then one or more ignition DTCs are generated (as well as possible OBD misfire DTCs, which are expected). In that case, the user must shut off the engine and MisGen3 power, and reconfigure the wiring as a set of “Y” connections to both blue and white banana jacks as previously explained. Then, any misfires subsequently generated will not raise any ignition DTCs, because the inductors inside the CCB create false voltage spikes to fool the diagnostic looking for flyback voltages to appear across the ignition’s power transistor drivers.
Most customers never need to create these false voltage spikes – because their ignition diagnostic does not monitor them — so Global has created a “Basic” version of the CCB box that does not include these inductors and other relevant components (including the blue banana jacks).
To summarize, if you create misfires with either a Basic CCB or a Classic CCB using only white banana jacks, and do not generate any ignition fault codes, then a Basic CCB is all that is ever needed.
Of course, even if all engines under test do not presently use an ignition diagnostic based on flyback voltage, it is still possible that a new ignition design may include such a diagnostic in the future. For this reason, Global can upgrade a customer’s Basic CCB to a Classic CCB by adding the missing components.
Contact Global for upgrade pricing.
Depiction of clipped flyback voltage during misfire events
Figures 6 and 7 depict clipping of the primary coil’s flyback voltage during misfire events.
Figure 6 MisGen3 creates misfire by severely clipping the flyback voltage spike of the coil primary
Figure 7 Electronics within the control module that monitor flyback voltage see a normal-appearing voltage spike at the power transistor because of inductors within MisGen3, even though the actual flyback voltage at the coil is clipped. This functionality requires connecting the misfire generator in a “Y” connection, which can only be done with a Classic CCB, not a Basic CCB.