Chart A-3 Engine Cranks But Will Not Run

Engine Cranks But Won't Run Chart A-3:

Engine Cranks But Won't Run:

Circuit Description:
This chart assumes that battery condition and engine cranking speed are OK, and there is adequate fuel in the tank. This chart should be used on 4.3L engines with CPI.

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

1. A "Service Engine Soon" light "ON" is a basic test to determine if there is a 12 volt supply and ignition 12 volts to ECM. No 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. If coolant sensor is below -30° C, the ECM will provide fuel for this extremely cold temperature which will severely flood the engine.

2. Voltage at the spark plug is checked using spark tester tool ST-125 (J 26792) or equivalent. No spark indicates a basic ignition problem.

3. Use an injector test light like J 34730-2B, BT-8329A or equivalent, to test injector circuit. A blinking light indicates the ECM is controlling the injector.

4. This test will determine if there is fuel pressure at the CPI unit and holding steady. Use fuel pressure gage J 34730-1 or equivalent. Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gage.

5. Checking resistance of the injector will determine if the injector is at fault.

Diagnostic Aids:
If no trouble is found in the fuel pump circuit or ignition system and the cause of a "Engine Cranks But Will Not Run" has not been found, check for:

^ Fouled spark plugs
^ EGR valve stuck open
^ Low fuel pressure. Related Tests, Information and Procedures
^ Water or foreign material in the fuel system
^ A ground CKT 423 (EST) may cause a "No Start" or a "Start then Stall" condition
^ Basic engine problem