Engine Cranks, But Will Not Run

Chart A-3 Engine Cranks Will Not Run:

Chart A-3 Wiring Diagram:

Circuit Description:

This chart assumes that battery condition and engine cranking speed are OK, and there is adequate fuel in the tank.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. A MIL (Service Engine Soon) "ON" is a basic test to determine if there is a 12 volts supply and ignition 12 volts to the ECM. No data may be due to an ECM problem. The engine will not start without reference pulses and therefore the scan tool should display RPM (reference) during crank. If RPM is erratic it is possible that the reluctor wheel on the crankshaft is damaged.

2. For the first two seconds with ignition "ON." or whenever reference pulses are being received, the scan tool should indicate fuel pump circuit voltage (8 to 12 volts).

3. Because the electronic ignition system uses two plugs and wires to complete the circuit of each coil, the companion spark plug lead should be connected to a good ground. If RPM was indicated during crank, the electronic ignition control module is receiving a crank signal, but no spark at this test indicates the ignition control module is not triggering the coils.


4. This test will determine if there is B + at the injectors. The injectors are powered by 2 fuses located in the underhood electrical center.

5. This test will determine if the ignition control module is not triggering the problem coil or if the tested coil is at fault. This test could also be performed by using another known good coil.

6. This test will determine if the ignition control module is not generating the reference pulse or if the wiring or ECM are at fault. By touching and removing a test light to 12 volts on CKT 647, a reference pulse should be generated. If RPM is indicated, the ECM and wiring are OK.

Diagnostic Aids:

A damaged reluctor wheel may cause a crank but will not run situation.