*Before performing diagnostic tests check for any fault codes that may be
If fault codes are present, clear them(battery disconnect) and crank
the engine for 10 seconds and recheck codes.
If codes are present repair them before continuing.
*These tests can also be run on 91 up(except T-3)but the DB/YL wire was
removed from the diagnostic connector so you cannot actuate the ASD as
it is listed in step #3.
*Due to the length of diagnostic charts and changes made from year to year
if specific diagnostics are needed for ASD,HEP,Coil Control circuits contact
me for specific info related to your year/model/engine.
1)Verify no spark by removing the coil wire from the distributor cap and hold
1/4" from a good ground.
Crank the engine for 7-10 seconds, spark should be strong and consistent
Count 1-2 sparks as No Spark.
Is spark present?
Yes...Recheck at a spark plug, if spark is not present at the plugs the issue
is with the secondary ignition(cap, rotor, wires)
***If spark IS present your issue is intermittent or not ignition related, move to fuel system diagnostics***
Distributor is turning, if distributor is not turning repair timing belt issue.
Coil wire is not open, check resistance with an ohmmeter,3000-5000 ohms
per foot. Repair as necessary.
Are distributor and coil wire OK?
3)Check ASD Relay circuit(84-90)(On 91-up do you hear the fuel pump cycle for 1 second with initial key on?)
Locate the underhood diagnostic connector
With the key on/engine off ground the DB/YL(dark blue/yellow) wire.
This will actuate the ASD relay.(A Code 42 will be set in memory)
Power (battery voltage) should be present at the + coil, DG/BK
(dark green/black) wire at the injector(s) and at the fuel pump.
You should hear the fuel pump running.
Is power present?
No...Repair ASD Relay circuit
4)Check HEP (hall effect pickup) circuit.
Remove the ground wire from the diagnostic connector.
Using a 12 volt test lamp connected to + coil and ground crank the engine.
The test lamp should illuminate.
Did the test lamp illuminate?
No...Repair the HEP circuit
5)Check coil control circuit
Using a 12 volt test lamp connected to - coil and ground crank the engine.
The test lamp should flash on/off repeatedly.
If the lamp flashed on/off but no spark...replace the ignition coil.
If the lamp did not light...replace the ignition coil
If the test lamp illuminated but did not flash...repair the coil control circuit.
MANUALLY ACTUATING THE ASD RELAY