I am getting no spark at all. I have changed the ignition module, new
distributor,coil checked and is fine. I have also changed cap, rotor etc
and I am at a loss as to what it could possibly be. It cranks over fine,
just no spark. Any suggestions would greatly be appreciated. This is a '94
fuel injected 302 (5L). Thanks again,Jon
Some methodical troubleshooting will be in order. If you don't have one, buy
a test light (a few bucks at any auto parts store). Turn ignition on and
check that you have +12V at the positive (usually red) primary coil
terminal. If no light there, you have a bad ignition switch or a bad
connection somewhere. OK so far? move the test light to the negative side of
the primary coil (green or some such) and have an assistant crank the
engine. The light should flicker at four times per revolution rate. If it's
flickering, suspect the high voltage winding on the coil or the high voltage
wire from the coil to the distributor. If it's steady, you have a bad
ignition module, bad connection to the ignition module, or (less likely) bad
pickup in the distributor. If no light on that side, disconnect the wire to
the negative side and probe that end of the coil with ignition on (if it's a
single connector, you may need to improvise a piece of wire to connect the
positive side of the coil with the connector removed). Still no light = bad
coil (open primary).
There are more possibilities, but hope this helps a bit.
I have tested as you have listed here and I get a steady light with the
ignition on and a ground with the ignition off. I have just put in another
new ignition module and pickup just in case but still , no spark!!What
might those other possibilities be?? Thanks.
Worth a shot, though SPOUT would have to be shorted to ground or to B+ to
make it kill ignition altogether.
But I am not yet convinced that it's not the HV side. What is the negative
side of the coil doing when cranking? On? Off? Or flickering (as it should)?
Seems that you have a problem in the primary (low voltage side) ignition
The way the circuit works is that a magnetic field is built in the coil by
running current through the primary and collapses just before the spark
should occur. The collapsing field induces a high voltage in the secondary
and an arc (spark) in the combustion chamber dissipates the stored magnetic
energy. Then the field builds up again, until the next firing. This cycling
is done by the ignition module that acts like a switch; it grounds the
negative side of the coil to close the circuit and opens it to break the
current flow and collapse the magnetic field. When the current is flowing,
the negative side of the coil is at ground potential, and the test light
will be off. When the module opens the circuit, the voltage at the negative
side of the coil is the same as at the positive (+ 12V), and the light is
briefly on. This will happen too fast for you to see if the engine is
running, but should be visible when cranking. If the car has a tacho, you
should see the needle bouncing around a bit when cranking - the instrument
is connected to the same spot on the coil. If the needle does not move, it's
just another indication that the primary circuit is not working.
If the light remains steady, the module is not doing its job for one reason
or another (the dimming is probably just the battery voltage dropping
because of the starter load).
If you ever worked on the old-style ignition with points, the module does
what the points used to do, and the basic troubleshooting idea is the
SPOUT is a single wire, going from the engine computer to the ignition
module. There is a connector on it that you can unplug. This line carries a
variable timing signal from the computer. If you disconnect it, the timing
becomes fixed, controlled just by the ignition module and is independent of
RPM or load. They provided a connector on this line, so you can disconnect
it for timing the distributor (more-or-less the same idea as disconnecting
the vacuum advance on the old style ignition).
I don't have the detailed schematic in front of me, but if I remember
correctly, the circuit is not bullet-proof, and a short somewhere along the
SPOUT line (including a defective computer) will stop the module from
working and kill the ignition altogether. Hence Backyard's idea to try with
SPOUT disconnected. You can't drive like that, but the engine should start
and run if that's the only problem.
Hope this long-winded story helps you. If you are still baffled, it's
probably time to donate a few bucks to your friendly auto mechanic. For one
thing, it's much easier to diagnose those things with better tools, like a
DVM and an oscilloscope...
Unfortunately I don't have the pinout or wire colors for the ICM (I
believe it is remote mounted on this vehicle), but also check for
power at the ICM, and PIP, SPOUT signals (those should be between 3
and 8.5 volts AC during crank)
The diagnostic flow chart leads to coil harness checks then checking
the grounds at the ICM and the CMP sensor. I can scan the flowcharts
but they refer to test harness and breakout box locations.
There is a "No start with SPOUT disconnected" routine,. I'm not sure
if that's what other posters are referring to....
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