Car cranks but wont start
ENGINE CRANKS BUT WILL NOT START
When the engine cranks normally but won't start, you need to check
ignition, fuel and"http://www.aa1car.com/library/compression.htm".
Ignition is easy enough to check with a spark tester or by positioning a plug
wire near a good ground. No spark? The most likely causes would be a failed
ignition module, distributor pickup or "http://www.aa1car.com/library/crank_sensors.htm".
A tool such as an Ignition System Simulator can speed the
diagnosis by quickly telling you if the ignition module and coil are capable of
producing a spark with a simulated timing input signal. If the simulated signal
generates a spark, the problem is a bad distributor pickup or crankshaft
position sensor. No spark would point to a bad module or coil. Measuring
ignition coil primary and secondary resistance can rule out that component as
Module problems as well as pickup problems are often caused by
loose, broken or corroded wiring terminals and connectors. Older HEI ignition modules are notorious for this.
If you are working on a distributorless ignition system with a Hall effect
crankshaft position sensor, check the sensor's reference voltage (VRef) and
ground. The sensor must have 5 volts or it will remain permanently off and not
generate a crank signal (which should set a fault code). Measure VRef between
the sensor power supply wire and ground (use the engine block for a ground, not
the sensor ground circuit wire). Don't see 5 volts? Then check the sensor
wiring harness for loose or corroded connectors. A poor ground connection will
have the same effect on the sensor operation as a bad VRef supply. Measure the
voltage drop between the sensor ground wire and the engine block. More than a
0.1 voltage drop indicates a bad ground connection. Check the sensor mounting
and wiring harness.
If a Hall effect crank sensor has power and ground, the next thing
to check would be its output. With nothing in the sensor window, the sensor
should be "on" and read 5 volts (VRef). Measure the sensor D.C.
output voltage between the sensor signal output wire and ground (use the engine
block again, not the ground wire). When the engine is cranked, the sensor
output should drop to zero every time the shutter blade, notch, magnetic button
or gear tooth passes through the sensor. No change in voltage would indicate a
bad sensor that needs to be replaced.
If the primary side of the ignition system seems to be producing a
trigger signal for the coil but the voltage is not reaching the plugs, a visual
inspection of the coil tower, distributor cap, rotor and plug wires should be
made to identify any defects that might be preventing the spark from reaching
its intended destination.----
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Feb 17, 2010 |
1996 Acura RL