Part 1 of 2

Chart A-3 Circuit Diagram:

Diagnostic Chart A-3 Engine Cranks But Will Not Run:

CIRCUIT DESCRIPTION:

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

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

1. A "CHECK ENGINE" light "ON" is a basic test to determine if there is battery and ignition voltage (12 volts) to the ECM. No ALDL data 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" tool should display engine speed during cranking.

2. If the engine speed was indicated during cranking, 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 flash, indicating the ECM is controlling the injectors. The brightness of the light is not important.

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 battery voltage on YEL/RED wire, a reference pulse should be generated. If engine speed is indicated, the ECM and wiring are OK.

DIAGNOSTIC AIDS:

1. Water or foreign material can cause a no start condition during freezing weather. The problem may occur during overnight parking in freezing temperatures. The engine may start after a few minutes in a heated shop.
2. An EGR valve sticking open may cause a lean air/fuel ratio during cranking. Unless the engine enters Clear Flood mode at the first indication of a flooding condition, a no start condition may be the result.
3. Low fuel pressure can result in a lean air/fuel ratio.