Ignition System Checks
| Check for an ignition system misfire:
Important: DO NOT perform this test for more than 2 minutes in order to prevent
damage to the catalytic converter.
- Start the engine.
- Disconnect one fuel injector (electrical connector) at a time
while observing engine RPM.
- An equal RPM drop on all cylinders (within 50 RPM) indicates
a common condition. Refer to
Rough, Unstable, or Incorrect Idle and Stalling
.
- No RPM drop on one or more cylinders indicates a cylinder specific
condition. Check for spark on the suspected cylinder(s) with a J 26792
spark tester or equivalent.
- If there is no spark, Refer to
Engine Cranks but Does Not Run
.
- If there is spark, check the spark plugs for any of the following
conditions:
- | Wet (fuel fouled) plugs. |
- | A terminal screw that is bent or loose (rotate and pull). |
- | A ceramic insulator that has cracks, carbon tracking or deposits
(red or black dust) |
- | A tip insulator that has cracks, carbon tracking, deposits (oil,
carbon, glazing, fuel additive), or is loose (rattles). |
- | A center electrode that is loose (wiggles side to side) |
- | An incorrect spark plug gap that is too large or too small. |
- If the ignition system components of the suspect cylinder pass
all checks, inspect the cylinder for mechanical or fuel delivery faults.
• | Check that the spark plug wire resistance does not exceed 30,000
ohms. |
• | Check the ignition system for moisture, dust, cracks, burns, etc. |
• | Run the engine and spray the secondary ignition system with water
in order to check for secondary voltage shorts. |
• | Check the CKP sensor engine reference signal with a scan tool.
Observe the Engine Speed parameter while operating the engine at the speed
of the concern. The scan tool should indicate steady and linear RPM readings
while running. If the erratic values, such as sudden spikes or drops in engine
speed are displayed, the engine reference signal is not stable enough for
the engine to run properly. Check for a short to ground in the CKP sensor
Ignition Reference Low circuit . A short to ground in the CKP sensor Ignition
Reference Low circuit will cause a faulty engine reference signal to be sent
to the PCM, but will not set a CKP sensor DTC (P0335). |
|