Why did this happen

[NC-Fordguy]

If some of you have read my other posts, you're familiar with my battle to get a 66 bronco running that had 30 miles put on it during the past 6 years. I rescued the bronco from behind a feed mill.

I rebuilt a couple of autolites 1100, replaced the stock distributer for a DUI, New plugs and wires, new battery, And I think I likely did a mexican hat dance and prayed to Mecca to get this thing to run.

A buddy or mine came over this past saturday who has an old willys jeep and told me about how the plugs like to foul out every couple years on his jeep. Suggested I put in new plugs even though I had installed new plugs a couple weeks earlier. Plugs looked good and spark was evident so I called BS.

Well after trying everything I succumb to his suggestion and off to Napa for new plugs we went. Installed the new plugs and the bronco fired right up. Some adjutments on timing, idle and mixture screw things were running well(slightly rich)

Question is what killed those new plugs and more importantly is this going to be a common occurance??? In nearly 30 years or turning wrenches I've never seen plugs foul out in such a short time

 

[jamyers]

That's odd.

I'd guess that there was something else that got fixed during the plug-swap, like plug wires not completely seated.

 

[rbohm]

8) ok, when you say spark was evident, did you check it at the plug, under pressure? many years ago in my high school auto shop class we had a spark plug cleaner/tester. what you did after you cleaned the plugs is hook up a high voltage plug wire, and start increasing the pressure that the plug saw. the theory was that the plug would act rather like it would in an engine. as you turned up the pressure, a bad plug would show itself off by not letting the spark jump the gap. being kids with a heightened sense of curiosity, we would test every plug that dame through the auto shop, new. used it didnt matter. we found that a bad plug would show a spark at standard pressure, but once the pressure started going up, the spark quit. we also found that some new plugs couldnt handle the pressure either. the best plugs handled pressure equivalent to an engine with a 25:1 compression ratio before the spark went out.

another thing that would cause a plug to not fire is glazing on the electrode, and you might not see this glaze without a magnifying glass. so what looks good to the naked eye, still doesnt work in an engine.

 

[fordconvert]

I have had the same thing happen on non running engines people brought me. I would pull the plugs and they looked fine, I would even hit them with a little carb spray and the air compressor. Must be that glaze thing. I even have one of those old school sand blasters and that sometimes wont even help.

 

[CobraSix]

I think something else was loose and got hooked up better in the swap.

I'm sure some plugs may go bad, but I've been using the same plugs in my truck for 120k miles. I just pull them out, hit them with a wire brush, check the gap and put them back in.

Who knows...just one of those mysteries. Like how did the plugs on my wife's 99 end up .025" over gapped when I know I set them not 30k miles prior (those were new plugs).

Just chalk it up as a lesson learned...one day you'll pull it out of no where on someone else and look like a demi-god of engine knowledge...

 

[rditz]

if you are convinced that the plugs were the problem, put them back in one at a time (start thruck between plug changes). if the truck starts to run rough after you've put in an old plug, you'll know that one is bad. take the next one and try again...

rod