I saw Lynn's recent thing about troubleshooting using a spark plug with .010 gap.  Then this exchange about there being adjustable gap plugs that can be used in addition to the "stock" non-adjustable plugs.

 

I can't remember the reason for using the "test spark plug gapped at .010".  Lynn, would you cover that again?

. . . I'm familiar with the fairly well know characteristic that the "spark" has more difficulty jumping the gap as the gap increases in size, and, as the compression increases.

. . . Thus, I associate the large .060 gap in my 1995 Ford Escort with a "high energy" (high voltage) coil pack electronic ignition system, as contrasted with my former 1954 Ford 6 cylinder with 7 to 1 or so compression ratio and old 30,000 volt (maybe) cylindrical coil and distributor system, then stock on most cars.

. . . . . A friend had a 1956 Chevy V8 "power pack" that had a miss:  We took my 6 known good plugs from my Ford and put in his 8.5 to 1 compression ratio V8 for trouble shooting (after grounding indivual plugs and not seeing much change in miss, so assumed the plugs were bad), so put my 6 "good" spark plugs, which weren't missing, into his V8 - still missed, so we mentally "eliminated" spark plugs as the culprit and started pulling the heads to look for bad valves.  A cooler, older head interrupted our course of action - we ended up by simply buying 8 new stock plugs for the V8 and the miss went away - my "known good" spark plugs that fired at 7:1 compression simply wouldn't fire in his  8.5:1 engine.

 

So, how does all this relate to a "process of elimination" troubleshooting of the fellow who recently had the severe miss in his rotary and discussion of ignition systems and bad coils?

. . .  I can see that a .010 gap plug ought to fire at about any compression and even with a crummy/degraded ignition system (bad/weak/cracked/arcing-through-cracks coil block).

. . . . .   If the coils are degraded, why would we want to get them to fire with the smaller gap in plugs?

 

Speaking of coil packs, I replaced a bad (cracked and arcing) coil block on the 1993 Escort which fixed the miss.  I later found on the internet an article about looking at the coils with engine idling AT NIGHT IN THE DARK and you could see sparks jumping out of the coil block onto the metal mount, etc.  The article said such coils could be "repaired" by coating/pototing them with epoxy or some such stuff.  That works - when my 1995 Escort developed the same problem, I repaired it rather than replacing it.

. . . So, I suggest as one of several trouble shooting steps to "visually inspect the igniter coils in the dark to look for visible arcing" - "then repair or replace as necessary".

 

David Carter