Question:My engine won't start. How can I tell if it's
getting spark?
Answer:If your engine has a distributor, the easiest
way to tell if the engine is getting any spark is to remove the
coil wire from the center terminal of the distributor cap (engine
off, of course, unless you want to find out the hard way it has
spark). Place the wire half an inch or so away from a metal surface
on the engine. Then have a helper crank the engine to see if
a spark jumps from the wire to the engine.
WARNING: Do not hold or touch the coil wire or a plug wire
while cranking the engine. If your no-start problem is not spark
related, you could get a rather nasty shock. The amperage is
rarely enough to cause any serious harm, but some people are more
sensitive to shocks than others.
If the engine cranks normally and you see a good, strong spark,
your no-start problem isn't ignition-related. Check the fuel
system and engine compression. No fuel (bad fuel pump or pump
relay) or a broken timing belt or chain could be causing your
problem.
If you don't see a spark, the ignition system will require
further diagnosis to isolate the fault. You may have a bad coil,
ignition module or distributor pickup.
DISTRIBUTORLESS IGNITION CHECKS
On engines with distributorless ignition systems, there is
no cap or coil wire. To check for spark, you have to remove a
plug wire from a spark plug. Insert a Phillips screwdriver, nail
or piece of wire in the plug wire boot. Then position the object
so it is about half an inch away from a metal surface on the engine.
Crank the engine and watch for a spark.
NOTE: You can buy an inexpensive "spark plug tester"
that makes testing for spark much easier. The tester resembles
a spark plug with the outer side electrode removed. The tester
also has an alligator clip on the side so it can be easily attached
to a ground on the engine. The coil wire or a plug wire can then
be attached to the tester, making it easier to see the spark when
the engine is cranked.
As before, a good spark means you're getting ignition -- at
least through the one plug wire you're checking. You can repeat
the test for another wire (or all of the wires) to see that spark
is getting through. If all are sparking, you have a fuel or compression
problem not an ignition problem.
If you don't see a spark when the engine is cranked, it means
one of several things: the plug wire is bad, the coil for that
particular plug is bad, or the ignition system isn't working.
Repeat the test on a different plug wire (not one that shares
the same coil). If you get the same result (no spark), the coil
pack module, ignition module or crankshaft/camshaft sensor is
bad. Further diagnosis will be required to isolate the faulty
component. This may require "scanning" the computer
with a plug-in scan tool to see if there are any ignition-related
fault codes.
