Back firing issue

[patrickt]

Originally Posted by rustyrims

is there another capacitor ? the one referenced is listed by MSD as only for radio noise suppression.

Capacitors are capacitors are capacitors, for the most part, their specs are just different. You can save a buck or two by buying a 26 kufd/25volt capacitor from Mouser but you want decent quality. And you can go up a bit on both numbers, it doesn't have to be exactly 26kufd. Before doing work on your car, remember to bleed the capacitor. To do that just disconnect your battery and hit the horn button (assuming your horn is wired to work without the key being on). You will hear the relay click and the horn might even make an audible burp noise. Mine does. That tells you your capacitor is holding but is now empty. You can leave your battery disconnected for quite a while and your capacitor will still hold a charge. Or, it can fail, like anything else, and it can fail open or closed. If it fails open then it's like it's not even there and it does nothing. If it fails closed then it's a short and will either blow the circuit breaker, if you have one, or burn something up or get so hot it fails open. MSD boxes are particularly sensitive to alternating current that is polluting your direct current feed to the box. A capacitor across the lines allows the AC to "take the shortcut" around the MSD box. I strongly recommend one. If you put your car's electrical system on an oscilloscope hoping to see a nice straight flat line at 13.7vdc you might be shocked at what you see. <pun>