My GT4 is only firing on one bank, what’s the best way to test the coils?
If I'm not mistaken you have to swap both the HT leads (talking the single lead going from the coil to the distributor) and the low voltage control side. I think the points or however you're controlling the spark end up being out of phase from bank-to-bank. -David Edit: Your original question was what is the best way... I don't know that this is the best way but this is how I would approach the problem. I would certainly defer to someone out there who had more experience.
Ok swapped coils and both seem to be working. Next is to test the two finned dooby whackers the coils sit in and under. What are they called?
From what I can tell looking at pictures on google, the setup for 79 has a finned heat sink attached to the coil and the resistor. Do you have an ohmmeter or digital multimeter? You can see if the resistors measure differently from bank-to-bank. I have no idea if this is a common failure. If I remember correctly, there is a relay that shorts out the resistors during cranking and opens up so the coils are connected to 12V through the resistors while running. Does your car have points/condensers or some other means of controlling the spark? This might be the place to start looking. Maybe something screwy with the distributor cap or rotor? Carbon button? Is it no spark or weak spark on the bad bank? -David
Found this under the fins says GM 146 4B25. Any idea what it’s from? I’ve punched in the number but nothing has come up.
