Detect Bad Spark Plug

[Richard Madison]

Looking for an easy (lazy) way to find which spark plug is not firing.

I watched a mechanic start the engine then pull the wire off each plug in turn to see when the engine showed no change. I guess this is the standard way to check plug firing but I don't have a wire puller. I'm looking for a quick and easy "touch and test" method.

Is there a gadget that lights up when touching a firing plug but stays off when touching a dead plug?  I've seen screwdrivers with a tiny bulb in the handle. The bulb glows when it detects current in the plug wire BUT does this test the wire or the plug? If the wire carries current even to a non-firing plug, then this tester will not find the dead plug.

Is there a lazy man's bad plug detector or do I have to buy a plug wire puller?

Richard, The Lazy.

[erickmarciano]

you can use a timing light and put the test clamp on each wire to see it it stobes evenly, assuming your wires are all good

1971 280sl
1962 VW
1954 Allstate vespa
1958 gs150 vespa
1962 gs160 vespa

[graphic66]

Sometimes you can get the engine hot then shut it off and just feel each spark plug while still in the engine. The cold one is the culprit.

[A Dalton]

<Is there a lazy man's bad plug detector or do I have to buy a plug wire puller?

Richard, The Lazy.
>>

 Yeah, an Ice pick w/ground wire attached.
 Crude, but lazy...

[Richard Madison]

Ice pick with ground wire...

Do I stab a plug with the ice pick to see if it bleeds?  )

Seriously, exactly how do I use a grounded ice pick to detect a dead plug?

Richard M, Engine Illiterate

[A Dalton]

Simple.

 You ground the wire from the ice pick to the block [ or any good gnd.] and you slip the pick under a boot at the plug or dist cap and that kills that plug.
 So... if you see a noticable rpm difference, then that plug is firing and that cyl. has compression.
 If no difference , then that one is not ..
 Once you find the one not firing, you have to do further testing as it can be a bad plug wire, bad plug, no compression, bad plug resistor, etc.
 If a plug wire is suspect, an easy test is to swap with a known good one  [ one you have already seen pass the firing test.]
 Of course, these are simple , quick test. The proper test procedure
 is to start with a compression test so you know where the engine stands before condemning ignition parts.

[bayleif]

Richard,
I just did this on my 280SL, pulling off the spark plug wires while the engine is running. I didn't have a wire puller, so I wore heavy work gloves. I felt no pain, and can't think of how it could be easier.

Chuck Bartlett
1969 Signal Red 4 Speed

[Mike Hughes]

You can always hook up a timing light to each of the plug wires.  The mis-firing plug will show up as an erratic light pattern, a dead plug will give no light pattern at all.

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)