scoobyis2cool
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| posted on 19/7/05 at 11:45 AM |
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Silly Question...?
I'm a bit confused about the procedure for testing spark plugs - I've read that you take it out and rest it on the engine to earth it,
then run the engine to see if you get a spark from it.
Now, if you're running the engine surely fuel is getting pumped into the cylinder with the missing plug? And coming out of the spark plug hole?
And getting ignited by the spark, destroying the engine, car, occupant and garage? I'm sure there's some explanation for why this is a
safe thing to do, can someone please let me in on the secret? 
Pete
It's not that I'm lazy, it's that I just don't care...
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Deckman001
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| posted on 19/7/05 at 11:47 AM |
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Place it on the engine but maybe not near the plug hole, it only needs to have an earth as you say so you can see it spark as the engine tries to
start or runs rough with only 3 spark plugs working in the bores !! 
Jason
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DarrenW
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| posted on 19/7/05 at 12:33 PM |
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If you are concerned and are more looking to see if you have sparking power at the end of the lead rather than testing the plug itself - car builder
solutions do a tester for a few pounds.
Looks like a handy device to have in tool box.
Other solution is to use spare plug and leave the 4 main ones in situ.
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David Jenkins
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| posted on 19/7/05 at 12:58 PM |
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You needn't worry about fuel igniting - if the plug is out the piston can't suck fuel through the carb. It's easier to suck plain
air through the plug-hole.
David
P.S. This presumes that you're running a conventional carb system - I can't speak for fuel injection systems!
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scoobyis2cool
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| posted on 19/7/05 at 01:14 PM |
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Thanks for the replies, seems much clearer (and less dangerous) now I've got a few spare plugs lying around so it sounds like that would be
the easiest way to test them.
Cheers,
Pete
It's not that I'm lazy, it's that I just don't care...
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DarrenW
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| posted on 19/7/05 at 01:33 PM |
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Another thing Pete - Theres no such thing as a silly question when doing the techy bits. Its far better to ask even if you think a million (or at
least several) others will see it as too basic than to risk getting hurt.
Ive tested for a spark loads of times before without giving a thought to the potential of 'loose' vapours. Thanks for the warning mate.
Ill probs be more careful myself now in the future.
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ReMan
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| posted on 19/7/05 at 06:00 PM |
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and , you're not aiming to "run" the engine , only crank it over a bit , you can take all 4 plugs out (or however may you've
got:cool so it def does'nt start, or swap one out for an old one and try it, if you're really worried........
www.plusnine.co.uk
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Jon Bradbury
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| posted on 19/7/05 at 06:07 PM |
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Or you could block the air intake so nothing gets sucked in!
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scoobyis2cool
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| posted on 19/7/05 at 07:14 PM |
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Just knowing that other people do it that way without trouble makes me feel a bit more confident! I wasn't sure if I'd missed some
essential fact that would prevent disaster 
Thanks for all the help, I'll let you know how I get on
Pete
It's not that I'm lazy, it's that I just don't care...
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ReMan
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| posted on 20/7/05 at 08:15 AM |
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And...........
I would gess you want to test a plug as you think one is faulty and the engine is running rough?
This can often be achieved just by pulling the cap off them one at a time and seeing which one makes no difference, the other 3 should make it rougher
still as you'll be down to 2 good cylinders.
www.plusnine.co.uk
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