Chart A-3 Engine Cranks But Will Not Run
Chart A-3 - "Engine Cranks But Won't Run" (Part 1 of 2):
Wiring Diagram for "Engine Cranks But Will Not Run".:
CHART A-3 (Part 1 of 2) 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.
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 volts supply and ignition 12 volts to Electronic Control Module (ECM). No Assembly Line Diagnostic Link (ALDL) may be due to an ECM problem and CHART A-2 will diagnose the ECM. If Throttle Position Sensor (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 crank.
2. No spark may be caused by one of several components related to the ignition system. CHART C-4 will address all problems related to the causes of a no spark condition.
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-34730-3 or equivalent.
4. 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.
Diagnostic Aids:
An 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. Check for fouled plugs. A defective cold start circuit or water in fuel line can cause a no start in cold weather. See CHART A-9. A defective MAF sensor may cause a no start or a stall after start. To determine if the sensor is causing the problem, disconnect it. The ECM will then use a default value for the sensor, and if the condition is corrected and the connections are OK, replace the sensor. Also check that injectors on both sides of engine will cause a test light to "blink". If not OK, check injector fuses. If above are all OK, refer to "Hard Starting" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.
Chart A-3 - "Engine Cranks But Won't Run" (Part 2 of 2):
CHART A-3 (Part 2 of 2) ENGINE CRANKS BUT WON'T RUN
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
5. Checks for 12 volts supply to injectors. Due to the injectors wired in parallel there should be a light "ON" on both terminals.
6. Checks continuity of CKT 467 and 468.
7. All checks made to this point would indicate that the Electronic Control Module (ECM) is at fault. However, there is a possibility of CKT 467 or 468 being shorted to a voltage source either in the engine harness or in the injector harness.
To test for this condition:
Disconnect all injectors Ignition "ON". Probe CKTs 467 and 468 on the ECM side of injector harness with a test light connected to ground. (Test one injector harness on each side of engine), There should be no light. If light is "ON" repair short to voltage, If OK, check the resistance of the injectors. Should be 10 ohms or more. Check injector harness connector. Be sure terminals are not backed out of connector and contacting each other. If all OK, replace ECM.