Advanced Engineering Tech - Internal Electical Circuit in GM's LS Ignition Coils
04-04-2007, 10:18 PM
Does anyone have a schematic or diagram of the internals of GM's smart ignition coils? Anyone know the patent number (s) that GM has on this?
04-04-2007, 11:37 PM
When you say "smart" ignition coils, I'm not sure that I follow. Each of the eight coils have a power amplifier of sorts for the primary winding of the coil. This is basically a transistor or solid-state switch that allows a small amount of current from the powertrain control module (PCM) to control a much larger amount of current through the primary winding of the coil. Like with a Kettering ignition system (has points and a condenser/capacitor), current flows through the primary winding of the coil until the magnetism level (called magnetic flux) saturates the laminated iron core of the coil (which is really a transformer). Then when the current is stopped through the primary winding, the magnetic field collapses almost instantly and this causes a very high voltage to be produced in the secondary winding. The current path for this voltage to discharge to ground (the cylinder heads/block) is from the coil, through the spark plug wire through the center electrode of the plug and across the gap of the plug which produces the spark.
The really different thing about these coils is that they have a built-in power amplifier that allows the PCM to control the coils with a very small amount of current. I hope that this helps you understand how they operate.
04-05-2007, 11:19 AM
Thanks Steve, yes that does help.
The coil module has separate signal reference and power grounds. In stock installations, the power ground connection is made to the cylinder head or engine block. I am relocating the ignition coils away from the engine, and I am trying to decide if it is better to connect the power gound to chassis, or whether to run a separate ground wire back to the block. Any insight on this?
04-05-2007, 11:55 AM
It really won't matter at all as long as you get a "good" ground. By that I mean a very low resistance path to the negative battery terminal. I'd advise you to find an existing ground stud on the firewall or somewhere near where you plan to relocate the coil packs. Then run a 12 or 14 gage ground wire from the ground stud to the coil packs. When you remove the nut from the ground stud, take a wire brush and clean the stud, the nut, any washers and all of the terminals well with the brush. Then get some silicone (like you'd use inside spark plug boots) and lightly coat all of these parts and tighten the nut snugly. The cleaning improves the electrical conductivity and the silicone provides a protective barrier to prevent future corrosion.
Unless you're doing this because you like the esthetic look of the clean valve covers, I wouldn't do this myself. The coil near plug principle that GM designed is technically superior to remote mounted coils. It won't make a lot of difference in the short run. But over the years, the GM design will be more trouble free and provide a slightly hotter spark.
04-05-2007, 01:36 PM
Good info. I'm relocating them primarily for engine serviceability access improvements (and the esthetic doesn't hurt).
Is the coil secondary winding's negative in common with the primary side negative?
Is there alot of EMI conducted down the power ground, and if so, would a chassis or engine ground result in less chance of EMI induced problems to other electronic equipment?
Does the power ground wire need to be short, to minimize inductance?
04-05-2007, 02:43 PM
Smart coils are able to turn themselves off, they have a dwell protection feature, many can handle their own dwell control as well, but the ecu handles the dwell on the LS1.
Here's a short snip from GMeSI for reference:
Each ignition coil has an ignition 1 feed and a ground. The PCM supplies a low reference and an ignition control (IC) circuit. Each ignition coil contains a solid state driver module. The PCM will command the IC circuit ON, this allows the current to flow through the primary coil windings for the appropriate time or dwell. When the PCM commands the IC circuit OFF, this will interrupt current flow through the primary coil windings. The magnetic field created by the primary coil windings will collapse across the secondary coil windings, which induces a high voltage across the spark plug electrodes. The coils are current limited to prevent overloading if the IC current is held high too long. The spark plugs are connected to their respective coils by a short secondary wire. The spark plugs are tipped with iridium for long life and efficiency.
04-06-2007, 08:34 PM
ok, so if you show voltage from the IC with a test light, but don't get spark from all 8 coils, is there something else along the line one would look for, like a bad ground to the harness?
04-06-2007, 08:50 PM
Your question kind of turns the corner from the concept of how these coils work and how they are controlled by the PCM to troubleshooting hints. If you'll send me a little more description of your problem in a PM about your problem, I'll be glad to help you try to sort this out.
This forum is more for the discussion of advance performance technology rather than a place to ask specific how-to questions.
Like I said, I'll be more than glad to try to help.