Part 1 of 2

Engine Cranks But Won't Run (Part 1 Of 2):

Ignition/Injector Wiring Diagram:

CIRCUIT DESCRIPTION:

Before using this chart, battery condition, engine cranking speed, and fuel quantity should be checked and verified as being OK.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. A "SERVICE ENGINE SOON" (SES) light "ON" is a basic test to determine if there is a 12 volt supply and ignition 12 volts to electronic control module (ECM). No assembly line data link (ALDL) may be due to an ECM problem, and CHART A-2 will diagnose the ECM. If TPS is over 2.5 volts, the engine may be in the clear flood mode, which will cause starting problems. The engine will not start without reference pulses and, therefore, the "Scan" should read rpm (reference) during cranking.

2. If rpm was indicated during crank, the ignition module is receiving a crank signal, but "no spark" at this test indicates the ignition module is not triggering the coil or there is a secondary ignition problem.

3. The test light should blink, indicating the ECM is controlling the injectors OK. How bright the light blinks is not important. However, the test light should be a J-34730 or equivalent.

4. This test will determine if the ignition 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 430, a reference pulse should be generated. If rpm is indicated, the ECM and wiring are OK.

DIAGNOSTIC AIDS:

^ An exhaust gas recirculation (EGR) valve sticking open can cause a low air/fuel ratio during cranking. Unless engine enters "clear flood" at the first indication of a flooding condition, it can result in a no start.

^ Fuel pressure: Low fuel pressure can result in a very lean air/fuel ratio. Chart A-7 Fuel System Diagnosis