The computer control module (ECM/PCM) uses information from the MAP and coolant sensors, in addition to rpm to calculate spark advance as follows:
Therefore, detonation could be caused by low MAP output or high resistance in the coolant sensor circuit, and poor performance could be caused by high MAP output or low resistance in the coolant sensor circuit.
The best way to diagnose what may be an ignition-related problem, first check for Diagnostic Trouble Codes (DTCs).
On OBD II systems, if the engine cranks and does not run or immediately stalls, the diagnostic test must be used top determine if the malfunction is in the EI system or is fuel related.
Ignition System Check
- Check for diagnostic trouble codes. If any are found, refer to the appropriate chart in Section 4.
- Turn the ignition switch ON . Verify that the Service Engine Soon light is ON.
Check the following:
- Throttle Position Sensor (TPS)-if over 2.5 volts, at closed throttle, check the TPS and circuit.
- Engine Coolant Temperature (ECT) sensor-if not between 22-266°F (30-130°C), check the sensor and circuit.
Disengage all injector connectors and install injector test light (J-34730-2 or equivalent) in injector harness. The test light should be OFF.
NOTEPerform this test on one injector from each bank.
Connect spark checker, (J 26792 or equivalent), and check for spark while cranking. Check at least 2 wires.
- If spark occurs, Connect the spark plug wires and check for fuel spray at the injector(s) while cranking.
If no spark occurs, check for battery voltage to the ignition system. If OK, substitute known good parts for possible faulty ignition parts. If not, refer to the wiring diagrams to track down loss of voltage.
Secondary Spark Test
The best way to perform this procedure is to use a spark tester (available at most automotive parts stores). Two types of spark testers are commonly available. The Neon Bulb type is connected to the spark plug wire and flashes with each ignition pulse. The Air Gap type must be adjusted to the individual spark plug gap specified for the engine. This type of tester allows the user to not only detect the presence of spark, but also the intensity (orange/yellow is weak, blue is strong).
- Disconnect a spark plug wire at the spark plug end.
- Connect the plug wire to the spark tester and ground the tester to an appropriate location on the engine.
- Crank the engine and check for spark at the tester.
- If spark exists at the tester, the ignition system is functioning properly.
- If spark does not exist at the wire, test the ignition coil, and other ignition system related components or wiring. Repair or replace components as necessary.