repeated spark plug failures

Sat May 24, 2014 12:11 pm

I have a neighbor that owns a Michigan Power Shovel with a Continental 6 cyl engine. Every 2 or 3 months the #1 spark plug fails, not oily or fouled, it just stops sparking. If you hold the plug wire close ot it the spark will not jump to the top of the plug, but will jump to ground. it does have carbon wires, but the spark from the wire will jump to ground a long way, just not to the top of the plug when it goes bad. Only happens on #1 plug. It is as if the center conductor of the plug is open. Any ideas on the cause?

Re: repeated spark plug failures

Sat May 24, 2014 2:55 pm

Will the dead #1 spark plug start firing if swapped with the #2 plug? And will the now #1 plug fire?

Still thinking, the spark has to go some place when it's not firing the #1 plug.

If it's a faulty spark plug, then I don't know why it would continue to only happen on #1 cylinder.

You have checked, ohmed the plug wire, the distributor cap, rotor, distributor cam lobe, spark plug gap, and distributor shaft for wobble.

One thing you could try is reducing the spark plug gap by .002".

Edit: Oscilloscope to see where the spark from #1 spark plug is going or is totally missing.

Re: repeated spark plug failures

Sat May 24, 2014 5:00 pm

No, #1 will not fire if put in another hole.
If you hold wire close to ground, it will jump a good 3/8 to 1/2 inch.
Just acts as if there is no conductor inside the plug.

Re: repeated spark plug failures

Sat May 24, 2014 6:04 pm

Out of curiosity, continuity test from spark plug cap to center electrode.

Manufacturing fault? But why only on #1 spark plug? Odds on that happening more than once would pretty long.

Re: repeated spark plug failures

Sat May 24, 2014 6:05 pm

John; This is an interesting problem. I wonder what the plug would do on a tester? Does he put in a new plug then, or clean it and get it working? (I would guess replace it, as you say it looks OK)

I have a tester and would like to play with one of the bad ones, just to see whats what. If you're interested in sending me one, PM me and I'll give you my snail mail address.

Just an after thought, resister plug or regular?

Re: repeated spark plug failures

Sat May 24, 2014 9:31 pm

Mark, cleaning does not work. I will see if he still has the one we just changed.

Re: repeated spark plug failures

Sat May 24, 2014 10:19 pm

If you can find the plug, contact the spark plug manufacturer. They typically have laboratories to investigate faulty products.

They may send a package containing a separate prepaid postal package. Happened to me. Oil filter with hole in side. Paid for a new filter, lost engine oil, engine clean up and a jacket with the company logo.

Re: repeated spark plug failures

Sun May 25, 2014 9:35 am

I think what’s probably happening is; the engine oil is fouling the spark plug. The anti oil burning additives that’s in the engine oil now is really hard to get off spark tips for conductivity. I’ve taken carb cleaner and even a finger nail file and still had a miss-fire issue.

I’d do what Eugene said:

Take an Ohm’s meter and connect from terminal to center electrode and see if the reading is the same as a known good spark plug. Next go from side terminal to metal case and see if the reading is the same as a known good spark plug. If all checks are the same the conclusion is center electrode and side terminal have a non conductive coating on it.

I’m also interested in what the cause is too.

Re: repeated spark plug failures

Sat Jun 28, 2014 12:14 pm

I'd put in a new spark plug and close up the gap a little. Some of the older engines had side gap spark plugs.

Re: repeated spark plug failures

Tue Jul 08, 2014 6:36 pm

Bad ignition wire?