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One common question in regards to MSD Ignition controls is “Why isn't 12V power on the orange (COIL +) wire?” The main reason 12V won't be present at coil + is because your MSD ignition is a Capacitive Discharge Ignition. Like all CD ignitions they use a large capacitor to discharge 420-480 Volts to coil + and coil – will normally be connected to ground. (That’s why you wont see +12V on coil +)
Most all stock ignitions are Inductive Ignitions, these will normally be connected to the + 12V ignition switch to coil + and coil – is connected to Points or the Factory Electronic Module. (That’s why you’ll see +12V on coil +)
If you suspect a spark plug wire to be open causing poor performance, check the resistance of each wire. By checking the resistance of each wire you will determine two things: That there is continuity (not open) and if there is too much resistance in the wire. Use an Ohm Meter and connect the terminals to the spark plug wire terminals. Use care to make sure there is good contact or the readings will be inaccurate. On MSD wires the resistance should be:
Heli-Core Wires (Blue): 150 - 1,200 ohms per foot
8.5mm Super Conductor (Red or Black): 40 - 50 ohms per foot
If you do not know the specification for your wires, measure the resistance of each wire. Remember to divide the length of the wire by 12 to get a "per foot" measurement. If one wire is out of that average spec, it is at fault
Solid Core Wires: You cannot run Solid Core Spark Plug Wires with an MSD Ignition Control. Solid Core wires do not suppress any Electro Magnetic Interference (EMI) which will interfere with electronics or rev limiters on your vehicle. A suppression style or spiral wound spark plug wire MUST be used.
If your timing seems to be jumping all over the place, check the following items:
What kind of timing light are you using? Many lights have trouble reading the MSD's capacitive discharge multiple sparks. Dial back timing lights are not recommended. Try another non-adjustable light and check the timing again. MSD offers a Timing Light, PN 8990.
Make sure you are not using Solid Core wires.
Inspect the routing of the Magnetic Pickup Harness. It should be routed clear of the coil primary wires and plug wires. It is best to route it along a ground plain such as the firewall, frame or engine block to form a shield around it, or replace the Black magnetic pickup cable with a shielded Gray cable PN 8862, which has a ground wire on one end.
Check the polarity of the magnetic pickup wires of the distributor. Reverse the connectors and check the timing again. For Analog ignitions the correct polarity is whichever orientation gives the most retarded timing. For Digital Ignitions the correct polarity is whichever orientation give the most advanced timing.
On Chevrolet engines, if the timing is retarding inspect for cam-walk. This is especially prevalent on engines with a chrome or stock type replacement timing chain cover that is actually bowing forward allowing the cam to "walk", due to thin stamping. To check this, wedge something in-between the water pump and timing chain cover to keep the camp from walking. If this corrects the timing fluctuation, replace the timing chain cover.
Worn distributor gear, inspect the distributor gear for excess wear or incorrect gear mesh if the gear is riding too high or too low on the cam gear. If correct the wear pattern should show the gear mesh in the center of the gear.