BrianX128 113 #1 Posted 2 hours ago (edited) Chasing an issue with no spark to cylinder #3 on my 52 vac, the plug gets extremely fouled and quits firing. If I take it out and sand it down clean and let the fuel evaporate in the cylinder or torch the hole real quick then it will run great all day. When it's acting up and is only running on three cylinders, if I hold the spark plug wire about an inch from the distributor then that cylinder will start firing again even if I don't clean it, but if I plug the wire back in then it stops firing. All 4 cylinders have 110psi of compression still, and I've replaced the plug wires and plugs but the problem is always cylinder 3. New cap made no difference either. Points are clean. The only thing I can even think of is it still has a ballast resistor on top of the engine, I could try bypassing that but what would you guys do? Nothing stands out given that it "can" run fine, no compression issues, and the problem always goes to the same hole. I've heard that weak spark can start working if you hold the plug wire away like I am and it "jumps", but I'm not sure why it only happens to this cylinder no matter what I do electrically. Edited 2 hours ago by BrianX128 Share this post Link to post Share on other sites
ri702bill 11,055 #2 Posted 2 hours ago It sounds like a shorting path to ground. Or maybe is it getting oil fouled?? Try switching the plug from #3 with another - see if it follows the cylinder or the plug... I have seen a bad plug before that when removed & grounded the spark jumped the gap just fine. Reinstall, and it would not work under compression. Changed the plug and it ran fine. Not so sure an inline spark checker would be of help - gives a false positive for the condition above... Share this post Link to post Share on other sites
BrianX128 113 #3 Posted 2 hours ago It stays with the cylinder, it's only done it on that cylinder. I've even taken the "dirty" plug out and put it in another cylinder and put a clean plug in the suspect one, and the dirty plug will fire fine in another hole. Tried switching the wires in case something was going on there as well, but problem stays with the hole. Ironically, this cylinder has slightly higher compression than the other three. It's probably closer to 115 while the other 3 are all either right at or slightly below 110. Hard to tell exactly with such small differences. Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,944 #4 Posted 2 hours ago When the plug fires with the wire held away from the plug you are increasing the plug gap which increases the spark voltage. With that happening one has to assume everything up to the plug is OK meaning the components are not leaking voltage to ground and the coil has the ability for higher output. Share this post Link to post Share on other sites
8ntruck 8,529 #5 Posted 1 hour ago (edited) I've got a small block Chevy in my old ugly orange truck with sketchy valve seals or maybe worn guides. Th3 #3 cylinder was fouling the plug. As a stop gap, i installed a plug with a higher heat range in that cylinder. That patch has been working for several years now. Probly ought to mention that I don't drive that truck very often. Edited 1 hour ago by 8ntruck 3 Share this post Link to post Share on other sites
BrianX128 113 #6 Posted 46 minutes ago Interesting thought, I'm not sure what the stock plugs even are. I've just been replacing them with what was in it after I inherited it from my grandfather. I'll check when I get home today and see what is actually in there. I know there were a set of auto lites and champions both in the little toolbox on the side. None of them have ever changed anything, but they could be the same heat too. Share this post Link to post Share on other sites
